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Night Sky Observations
A Beginner’s Guide
An overview in how to start with
night sky observations
…on your way to becoming an amateur astronomer
v.3
Compiled by Gerrit Penning for:
© Bloemfontein Centre of the
Astronomical Society of Southern Africa
Created February 2007.
Course material for Sky Watching beginners | © ASSA Bloemfontein 2007 | www.assabfn.co.za | [email protected]
1
Index
1. What there is to learn in Astronomy and Sky Watching.............................3
1.1
1.2
1.3
Astronomy
Sky Watching
Terms and Definitions
2. Astronomical data for your location..........................................................6
3. Introduction to Amateur Astronomy: Where does your interest lie?.........7
3.1 The Path to Amateur Astronomy
4. Sky Watching for the beginner..................................................................8
4.1 The Moon and Planets
4.2 Stars and Constellations
4.3 Deep Sky Objects
5. Telescopes................................................................................................12
5.1 The Basics of Telescopes
5.2 Using Binoculars for astronomy
6. Workshop in Night Sky Observations........................................................14
6.1 Using a sky map to find stars and deep sky objects
6.2 Using a planisphere for orientation
6.3 Using software to plan your observing sessions
7. Preparing for Night Sky Observations......................................................16
Course material for Sky Watching beginners | © ASSA Bloemfontein 2007 | www.assabfn.co.za | [email protected]
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1. What there is to learn in
Astronomy and Sky Watching
1.1 Astronomy
Astronomy is a huge subject: as big as the Universe itself! Astronomy can be divided into:
- General interest astronomy
- Amateur astronomy
- Professional astronomy
General interest astronomy is for those who have an interest in the subject, but choose not to make it their
hobby or their profession. They like for instance, to simply read popular books about it and watch television
documentaries.
Amateur astronomy is for those who choose to go a bit deeper into the subject, but still not pursue it as a
career. Amateur astronomers are typically those who make it their hobby (for the fun and enjoyment of it!), and
some even contribute towards professional research, (though not necessarily getting paid for it). Many amateurs
begin their interest in the hobby through Sky Watching, and some even become specialized in it.
Professional astronomy is chosen by those who want to make it their career: they study it at a tertiary
educational institution, usually in the field of Astrophysics, and “get paid each month” for the work they do.
Astronomy is one of the oldest sciences. It is also one of the few remaining sciences where the amateur
astronomer can make a contribution towards professional research. There are few things in life as satisfying as
seeing your name published in a professional journal, because of your assistance to professionals.
The formal definition: Astronomy is the science of celestial objects (such as stars, planets,
comets, and galaxies) and phenomena that originate outside the Earth's atmosphere. It is
concerned with the evolution, physics, chemistry, meteorology, and motion of celestial objects, as
well as the formation and development of the universe. The word astronomy literally means "law of
the stars" and is derived from the Greek “astronomia”. – Wikipedia.org, “Astronomy”.
Background to Astronomy: Sizes and Distances
(Based on the multi-media presentation “A Zoom Journey to the Stars” by the Boyden Science Centre.
Note that “1 billion” refers to “1 000 million”).
Our home in the Universe
All the stars that you can see with your eyes from the Earth are located in the Milky Way galaxy. 6.5 billion
people orbiting around the Sun (Earth’s nearest star), part of a solar system of 8 official planets, the solar
system in turn orbiting around the centre of the Milky Way galaxy once every cosmic year (225 million years).
Age and time
Our Sun is about 5 billion years old. The planets formed during the same time out of a disk of gas and dust
orbting the Sun. So far, large telescops have managed to see almost 14 billion years into the past – very close
to the moment of creation. When you look at an object 8 light years away from the Earth (e.g. the star Sirius),
you see the star how it looked like 8 years ago! Light travelled 8 years, at the speed of light of 300 000 km/s,
before reaching the Earth. If Sirius were to explode today, you will only see the explosion in 8 year’s time...
Distances
The moon is on average 380 000 km from the Earth – only a few day’s travel with a space probe. The Earth is
150 million km from the Sun (1 AU). This is only a few year’s travel by satellite, but a 142 year journey with a
car travelling at 120 km/h! Proxima Centauri, part of the Alpha Centauri system and also the nearest star to our
Sun, is 4.3 light years away (4x 9 500 billion km). If you travel at 70 km/s (the speed of the fastest man-made
satellite to date), it will take you over 18 000 years to reach Proxima Centauri.
Course material for Sky Watching beginners | © ASSA Bloemfontein 2007 | www.assabfn.co.za | [email protected]
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Sizes
The Earth is 12 756 km in diameter - about 3 times the diameter of the moon. 11 Earth’s can fit into the
diameter of Jupiter and 10 Jupiters (110 Earths!) can fit into the Sun’s diameter. The star Betelgeuse, 430
lightyears away from the Sun in the constellation of Orion, is 620 times as big as the Sun! The Milky Way galaxy
is 100 000 light years in diameter. Andromeda galaxy, 2.4 million light years away, is the nearest large spiral to
the Milky Way (visible with the naked eye in Spring).
Galaxy clusters
Our Milky Way galaxy, together with two of its satellite galaxies the Large and Small Magellanic Clouds, are part
of the so-called “Local Group” of galaxies. It contains about 30 to 40 galaxies. The Milky Way and Andromeda
are the largest members of the group, with M33 being 3rd in size. Our Local Group is part of the Virgo Super
Cluster of galaxies. The Virgo Super Cluster, together with many other super clusters, make up the Universe.
The Universe
The Universe contains billions of galaxies, each containing millions or billions of stars. Under the influence of
gravity, these galaxies grouped together into local groups and super clusters. Only 4% of the Universe consists
of ordinary, visible matter. 22% is said to consist of dark matter (an unknown substance that generate gravity,
but which does not emit light). 74% of the total energy-mass distribution of the Universe consists of the
hypothetical substance called “dark energy”. The shape of the Universe isn’t exactly known. What lies outside?
Is there an outside? Where happens to matter when it falls into a black hole? So many questions still
unanswered!
Other interesting objects inlcude red giant and white dwarf stars, supernovae explosions, pulsars and neutron
stars, black holes, quasars, active galaxies, ...and many more.
1.2 Sky Watching
Sky Watching is a casual term used to describe people going outside during the night and looking at objects in
the sky. It is part of Astronomy, but on a more practical level. It is not something done by professional
astronomers, but more so by amateurs. Most amateurs start off with sky watching, and some even become
really good at it. For instance, it is possible to learn all 88 constellations by heart!
For the beginner, sky watching means looking at the moon, planets, stars, constellations and deep sky
objects. For the more advanced observer it can mean studying the surface of the moon, observing planetary
phenomena, knowing the distances and other attributes of certain stars, knowing the constellations by heart and
searching for deep sky objects with a binocular or telescope while sketching or photographing them.
This course deals mainly with Sky Watching, on a practical beginner’s level. As you become accustomed to
“what’s up in the night sky”, you’ll quickly find out what you like most. You’ll realize where your main interest
lies and what fascinates you most about all these objects. You can then start moving into amateur astronomy
and study a specific field that you find most enjoyable. A new world will open to your eyes…
Sky Watching is as simple as going outside and learning the positions of a few constellations. It’s about
knowing which stars are the brightest and which are the nearest. It’s about knowing what phases of the moon
are currently visible and which planets you can see at what time of the year. It’s about picking up a binocular
and finding a few deep sky objects – even those that you can see from our light polluted city skies.
(Die Afrikaanse term wat hiervoor gebruik word is “Naglugwaarnemings” of meer informeel “Sterrekyk”).
Behind the practical side of sky watching, are a few terms and definitions that you will have to get
accustomed to. Make sure you know what words like “magnitude” means, “celestial sphere”, “constellation
boundary”, “Alt-Azimuth”, “Greenwich Mean Time / Universal Time”, “South African Standard Time”, “Zenith”,
“Meridian”, “Ecliptic” etc. And most of all make sure you know where north, south, east and west is!
Course material for Sky Watching beginners | © ASSA Bloemfontein 2007 | www.assabfn.co.za | [email protected]
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1.3 Terms and Definitions
Astronomy terms and definitions
Orbit: The path of an object moving around a second object or point. “The Moon orbits the Earth”.
Kelvin (K): Zero K is absolute zero, equal to minus 273 degrees Celsius; ice melts at 273 K (0° C)
Astronomical Unit (A.U.): The average distance from the Earth to the Sun, approximately 150 million km.
Light Year: The distance travelled by light in one year = 9 500 billion km (63,240 AU).
Parsec: The distance at which a star would have a parallax of one arc second with a baseline of 1 AU (the mean
Sun-Earth distance). A parsec is equal to 3.26 light years or 206,265 AU’s.
Binary system (double star): 2 stars orbiting a central point. More than 50% of stars are doubles or multiples.
Accretion: Accumulation of dust and gas around a body (like a star).
Cosmos: The Universe. The word is derived from the Greek, meaning 'everything'.
In this course, 1 billion refers to 1 000 million.
Sky Watching terms and definitions
Greenwich Mean Time / Universal Time: The local time at the 0 meridian passing through Greenwich,
England; it is the same everywhere, anytime!
South African Standard Time: GMT +2 hours. If the GMT is 15h00, SAST will be 17h00.
Constellation: A pattern of stars connected with imaginary lines to form a figure in the sky.
Constellation boundary: The whole sky is divided into 88 official “patches” and these patches are the areas
that the constellations take up in the sky. Each constellation’s area has an official boundary.
Magnitude: The brightness of stars compared to each other. The lower the magnitude, the brighter the star.
Celestial sphere: The sky appears like a round balloon enveloping the Earth. The sky is also known as the
celestial sphere, which has a celestial equator as well as two celestial poles.
Ecliptic: The ecliptic represents the disc on which the planets are situated around the Sun. The ecliptic is the
line in the sky on which the planets, moon and Sun all appear to move, as seen from Earth.
Zodiac: The zodiac is the area in the sky in which the 12 constellations of the Zodiac are situated. It is in the
same area as the ecliptic: stretching slightly above it and slightly below it, like a “belt.”
Alt-Azimuth: An easy coordinate system. Altitude is measured from the horizon to the zenith (the point directly
above you). The horizon is equal to 0 degrees and the zenith is 90 degrees. Azimuth is the 360 degree circle
around you, 0 degrees being due north, 90 degrees east, 180 degrees south and 270 degrees west. 360
degrees is north again (also equal to zero).
Right Ascension/South Declination: A more complicated coordinate system, used with star charts and to
plot the positions of stars and deep sky objects.
Zenith: The point directly above you, e.g. the point 90 degrees from the horizon.
Meridian: An imaginary line that runs from north all the way to south over the sky, through your zenith.
Culmination: When an object moves anywhere over the meridian, it is said to “culminate”.
Degrees, minutes, seconds: Distances between objects in the sky is measured in degrees, minutes and
seconds. A full hand with spread out fingers equals 20 degrees. A fist = 10 degrees. A thumb = 2 degrees.
Meteor: a small piece of dust or rock entering the atmosphere and burning up due to high speed which builds
up ram pressure. Incorrectly referred to as a “shooting star”. If it hits the Earth, it is known as a “meteorite”.
Occultation: When one object moves in front of the other, it occults (obscures) the object at the back.
For a complete listing, visit http://www.r-clarke.org.uk/glossary.htm or page 112 of the 2007 Sky Guide.
Course material for Sky Watching beginners | © ASSA Bloemfontein 2007 | www.assabfn.co.za | [email protected]
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2. Astronomical data for Bloemfontein
Bloemfontein Geographic Coordinates
Boyden Observatory Coordinates
Breedtegraad (Latitude): 29 degrees, 7 minutes South
Lengtegraad (Longitude): 26 degrees, 11 minutes East
In decimals it will be:
-29.13 degrees South and 26.2 degrees East
Elevation: 1423 meters (4 269 feet)
Latitude: 29 degrees, 2 minutes South
Longitude: 26 degrees, 24 minutes East
In decimals it will be:
-29.03 degrees South and 26.43 degrees East
Elevation: 1418 meters (4 254 feet)
Time zone: GMT +2
Time zone: GMT +2
Bloemfontein neighbourhood coordinates
Name
Latitude
Longitude
Bayswater
Distance (km)
6.1
-29.083
26.233
Elevation
1389 m
Bloemspruit
6.7
-29.133
26.250
1372 m
Dan Pienaar
4.9
-29.083
26.217
1416 m
Fichardtpark
1.9
-29.133
26.183
1424 m
Generaal de Wet
4.0
-29.150
26.200
1444 m
Universitas
2.5
-29.117
26.183
1418 m
Handy web links for night sky observers
•
•
•
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Satellite fly-over times (ISS, Hubble, Iridium flares etc): www.heavens-above.com
Weather predictions: www.weathersa.com / www.1stweather.com / www.weatherphotos.co.za
Infrared Weather map for amateur astronomers updated regularly:
www.weatherphotos.co.za/clouds-cloud-cover.html
Google Earth: http://earth.google.com/
Astronomy in Southern Africa
Astronomical Society of Southern Africa: http://assa.saao.ac.za (with links to other Astronomy clubs in SA)
SAAO Cape Town and Sutherland: www.saao.ac.za
South African Large Telescope (SALT) at Sutherland: www.salt.ac.za
Boyden Observatory, Bloemfontein: www.uovs.ac.za/boyden
Hartebeesthoek Radio Telescope: www.hartrao.ac.za
HESS Gamma ray telescope: www.unam.na/research/hess/welcome.htm
Square Kilomter Array and meerKAT project: www.ska.ac.za
Astronomy in Bloemfontein
Bloemfontein’s Astronomy Society: ASSA Bloemfontein Centre
The region’s amateur astronomy club is suited for those who want to go deeper into astronomy and
even make amateur astronomy their hobby. There are four quarterly meetings per year and various other
activities in the form of workshops, observation evenings, courses etc.
U can also participate any of the club’s practical activities:
Deep Sky Observations, Comets and Meteors, Astrophotography, Historical research, Solar
Observations and even telescope building. Meetings are usually at Boyden Observatory, or in the city.
For more information, please contact Gerrit Penning at 084 429 9080 or Jacques van Delft at
082 812 5907 E-mail: [email protected] . Visit the club’s website at www.assabfn.co.za for
comprehensive information and the year’s calendar. Member fees: R50 per individual per year or R75 per
family per year. ASSA Bloemfontein is affiliated with National ASSA, an organisation that consists of
professional as well as amateur astronomers. Anyone can join national ASSA – http://assa.saao.ac.za.
Boyden Observatory and Science Centre: Boyden houses the third largest optical telescope in Southern Africa,
used for professional research. The Science Centre is open for group reservations. To reserve a group booking phone Dawie
van Jaarsveldt on tel: 051-401 2561. Boyden is owned and operated by the University of the Free State.
Friends of Boyden: An organization fostering wider public appreciation of Boyden Observatory and supporting its
educational outreach activities. www.assabfn.co.za/friendsofboyden. Anyone is welcome to join!
Contact: Braam van Zyl, 051-436 7555 (h). Planispheres available from the Friends.
Course material for Sky Watching beginners | © ASSA Bloemfontein 2007 | www.assabfn.co.za | [email protected]
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3. Introduction to Amateur Astronomy
Where does your interest lie?
3.1 The Path to Amateur Astronomy
Once you’ve laid down a solid foundation in beginner’s astronomy, you can move on into a field of amateur
astronomy. There are no “official” fields as with subjects in University, but a body like ASSA has identified a few
fields that seem to fit the system well. Here are a few examples of fields that you can consider in amateur
astronomy.
Areas in amateur astronomy (incl. some where you can make scientific contributions)
The first 4 are those that are included in more detail in this course, but on a non-scientific beginner-level.
T
H
I
S
C
O
U
R
S
E
1. Lunar Observations:
Learning the names of surface features, looking for transient phenomena
2. Studying Planetary phenomena:
Observing the moons of the planets, changes on surface, occultations.
3. Night sky observations: recognize and navigate the Stars & Constellations
Though there aren’t direct scientific contributions through this field, only a handful of amateurs can recognize more than 30
star names and all 88 constellations. It’s where fun meets passion, and it’s not difficult to do at all…
4. Deep Sky Objects: Many amateurs observe deep sky objects through binoculars and telescopes, mostly to
appreciate its pure beauty. Some objects however, need follow-up to clarify data in certain deep sky catalogues. You can even
compile your own deep sky lists. A minimum of a 10x50 binocular and a minimum of a 6 to 8 inch telescope are
recommended.
5. Solar Observations:
You can count sunspots, observe flares, study the effects of the Sun on Earth, and more.
6. Comet and Meteor observations:
Counting meteors during meteor showers; observing the brightness,
size and position of comets and determining the length of their tails.
7. Astrophotography:
Photographing celestial objects and phenomena.
8. Telescope making:
Building your own telescope, grinding mirrors, inventing telescope accessories etc.
9. Educational/public outreach: Sharing your passion in astronomy with children and the public.
10. Historical research:
Investigating our astronomical past; solving age-old mysteries!
11. Dark sky awareness:
12. Satellite tracking:
Informing the public, corporations and government about the threat of light pollution.
Using telescopes to track the paths of satellites (even classified spy satellites).
13. Double stars, variable stars, occultations, supernova and nova hunting,
exoplanet search, asteroid search and tracking, radio astronomy, spectroscopy.
These are various specialized fields undertaken by amateurs, but with direct professional contributions as a result.
14. Armchair astronomy: Enjoying the facts & theory from the comfort of your living room.
15. Computer software:
Knowing what astronomy software to use, the latest versions, what are the best, where
to find it. Knowing which websites to visit and how to effectively use the applications for a specific purpose.
Course material for Sky Watching beginners | © ASSA Bloemfontein 2007 | www.assabfn.co.za | [email protected]
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4. Sky Watching for the beginner
What is there to look at in the night sky? This chapter consists of:
4.1 The Moon and Planets
4.2 Stars and Constellations
4.3 Deep Sky Objects
4.1 The Moon and Planets
Both the Moon and planets are easy targets for beginners. Study the phases of the Moon
and know the positions of the brightest planets: then you’re half-way there!
a) Our Moon: Lunar Observations
The Phases of the Moon
Be sure to know when the moon rise or sets, but even more importantly: know the phases of the moon. It will
help you plan your observing sessions, as full moon makes deep sky observations near to impossible. The
phases can be seen on most calendars, but also in Sky Guide or with a computer application like MoonPhase.
Understanding the Moon’s orbit
The Moon takes 29.5 days to orbit the Earth once. The reason why the same side of the Moon always faces the
Earth is because it takes the Moon almost 29.5 days to make one orbit around its own axis too!
The planets are all situated on the ecliptic. The Moon does too, but its orbit is somewhat inclined compared to
the ecliptic, meaning its orbit is tilted. Have you noticed that the moon does not always travel along the same
path month to month? Sometimes it is much further north and other times further south. This is because of the
moon’s orbit being inclined to that of the Earth’s orbit around the Sun.
Lunar Eclipses
A total lunar eclipse is when the Moon fully moves into the dark part of the Earth’s shadow (into the umbra).
During a partial eclipse, the Moon only moves into the outside part of the shadow (the penumbra). Eclipses only
happen during full moons. Can you think why?
Observing the Moon from your location
The best time to look at the moon is from crescent to first quarter and last quarter to crescent – otherwise the
Moon is too bright and the surface features are engulfed in the light. You can however, use lunar filters on your
telescope to block out the brightness. Do yourself a favour and start to note the position of the Moon and its
phase at that particular time: suddenly you’ll have knowledge few of the general populace have!
What can you see on the Moon? Using a telescope or binocular
Surface features include Maria, the dark smooth plains of hardened lava. You’ll also find many craters formed
mostly hundreds of millions of years ago. There’s impact basins, crater rays, mountain ranges, riles, domes,
wrinkles and valleys.
Lunar facts
•
•
•
•
•
•
The diameter of the moon is 3 476 km and that of the Earth 12 756 km.
The moon is on average 380 000 km from the Earth.
The moon’s orbit around the Earth is elliptical and not a circle: this gives rise to a change in the moon’s
distance from the Earth.
There were in total 6 landings on the moon during the Apollo mission, from 1969 to 1972. Apollo 11
landed Neil Armstrong, and he became the first man on the moon.
A total of 382 kg of rocks were brought back from the moon from all missions.
The moon has no atmosphere and virtually no geological activity.
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b) Observations of the Planets
There are few things as beautiful as planets in the sky close to each other or to the horizon after sunset or
during sunrise. The positions of planets change compared to the fixed stars in the background. This means that,
each month, your sky will look different and you need to constantly refresh your mind with the latest planetary
positions. See your Astronomy CD, folder 3 (Night sky observations) for planetary terms and definitions.
Definitions of a planet and dwarf planet
A Planet:
(a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it
assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.
Dwarf planet:
(a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so
that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighbourhood around
its orbit, and (d) is not a satellite.
Understanding the positions of the planets in the solar system
If you want to understand the positions of the planets in the solar system, compared to their positions in the
sky, you will have to look at a diagram of the solar system from the top.
It sometimes happens that planets are situated quite close to each other in the sky, making pairs or even trios
only a few degrees from each other. These can be splendid sights and it is recommended that you keep abreast
of future planetary configurations by referring to the Sky Guide booklet.
The unaided eye planets vs. the aided eye planets
Some planets have been known since ancient times, as they were visible with the naked eye. They include
Mercury, Venus, Mars, Jupiter and Saturn. Uranus and Neptune (as well as Pluto) have to be observed with an
optical instrument like a telescope. Uranus can be seen with a binocular and looks like a star if you know exactly
where it is situated. You need a telescope to search for Neptune.
Knowing when the planets are visible: rise and set times
How do you know what planet in the sky is which? The best sources are yearbooks for Southern Africa (e.g. Sky
Guide Africa South) and also planetarium software on your computer like Stellarium. If you study the planets’
positions on any given night and morning and you regularly look at them subsequently, you will always know
exactly which planets are in the sky. Before doing night sky observations, be sure to study up on the positions
of the planets as they make great unaided eye and telescope objects.
Observing the planets: what you can see
As a beginner,
Mercury:
Venus:
Mars:
Jupiter:
Saturn:
Uranus:
Neptune:
the first things that you will notice about the planets are:
Mercury is quite small, but you can see a round disc and sometimes a small phase.
Venus can clearly be seen as having a very bright disc and its phases are evident.
Mars has a reddish shine and with larger telescopes you can see surface features like dust
storms (the darker areas) and sometimes even the white colour of its icy polar caps.
Jupiter’s cloud bands can be seen and with a larger telescope, the Great Red Spot. In addition,
even with a small telescope you can see its 4 largest moons (it has over 60 in total...)
Saturn’s rings are an impressive sight through almost any telescope. Look for the Cassinidivision, a gap between its rings. You can also see some of its moons.
Uranus looks like a star out of focus through a telescope, but a disc can clearly be seen.
Neptune will look like a star through a small telescope, a larger telescope will show its disc.
Occultations
When a planet moves in front of a star, blocking it from view, the planet “occults” the stars. These are superb
events and once you’ve seen one, you can easily get hooked on occultations… See the Sky Guide for the best
planetary occultations.
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4.2 Stars and Constellations
Stars
For an amateur astronomer, it is recommended to know at least the first 5 to 10 brightest stars by name and
their magnitudes (brightness) – refer to appendix A.
Number of stars: on any given night, when you are outside of the worst city lights, you can see 3,000 stars
with the unaided eye. There are billions of stars in our Milky Way galaxy however.
Star proper names: The brighter stars have “proper” names given to them. These are mostly Arabic in origin.
Some names are easy, such as Spica and Atria. Others sound quite flamboyant, like Zuben El Genubi and Ras
Alhague. Knowing many of the proper names is something few amateur astronomers can do. It takes time to
learn and lots of revision to stay “in touch”. Lean a few – you won’t be sorry.
The Greek Alphabet: Not all stars have proper names. The brighter stars have Greek letters assigned to them.
It is highly recommended that you learn the Greek Alphabet for easier star map navigation (at least alpha tot
zeta). Have the alphabet always handy when attempting to read off star maps.
Distances: it helps to know which stars are closest to our Sun. Learn the first 5 or 6 for a start. Also know the
distance (in light years) to some of the more prominent stars in the sky, like Sirius, Betelgeuse, Canopus and
Alpha Centauri.
Colours: You will note that stars have different colours. This is not an optical illusion; this is because they DO
have different colours! Red stars are especially prominent (e.g. Antares, Betelgeuse). Blue and white stars are
the hottest, while red stars are the coldest. The colouring is due to the physical properties of the stars.
Luminosity: It is necessary to understand that one star may be 10 times further than a foreground star, but
may shine brighter. Stars vary in their “luminosity”.
Magnitude: to be knowledgeable in night sky observations means to be knowledgeable in what “magnitude” is
and what the magnitudes of the brightest stars are. “Magnitude” is used to compare the brightness of stars as
seen from Earth. The lower the magnitude, the more the star’s brightness. A star with magnitude 2 is brighter
than a star with magnitude 4. The star Sirius (brightest star in the night sky) has a magnitude of -1.4. Keep in
mind that a difference of 5 magnitudes corresponds to a factor of 100 in intensity.
Stars twinkle because of atmospheric turbulence: light waves from the stars get bounced around in the
atmosphere on their way to your eyes. The more heat or fog in the sky, the worse the “seeing” gets. Planets do
not twinkle – can you think why?
Try to take notice of a few bright double stars in the sky and even variable stars (some amateurs specialize
in the latter two). Most stars are either double or multiple stars, unlike our Sun which is a “loner”!
Constellations
There are 88 official constellations, whose boundaries were set by the IAU in the 1920’s.
Only 6 constellations cannot be seen from our southern latitudes in its entirety. Knowing at least 12 of the
most important constellations is essential for every amateur astronomer who wants to perform proper night sky
observations. 24 are recommended, 36 will do just fine, but 82 will take the crown!
Constellations are important for: finding your way around the night skies, determining whether a certain object
will be in the sky during a specific time of the year and assists in locating deep sky objects quicker with
binoculars and telescopes. Most constellations were created by the ancient Greeks and Romans, while many
southern constellations were created by sea farers and astronomers visiting South Africa centuries ago.
See Appendix B for a list of the constellations. It sometimes takes imagination to see the figure in the
constellation which it is suppose to represent. The lines between the stars of a constellation are not official! You
can even draw your own lines connecting the stars. The boundaries of the constellations however, are official
and cannot be tampered with…
Course material for Sky Watching beginners | © ASSA Bloemfontein 2007 | www.assabfn.co.za | [email protected]
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4.3 Deep Sky Objects
Deep Sky objects are the favourite field in sky watching for many experienced observers and are usually the
reason why amateurs buy or build telescopes. Anyone can start off with deep sky objects. In fact, some are
even visible with the naked eye! Many can only be appreciated through a binocular (and not a telescope)
because they are so big. Thousands of the smaller, fainter ones are visible with a telescope.
As a deep sky observer you can try to see how many objects on a deep sky list you can find. The advanced
deep sky observer will search for faint or elusive objects and even write a report on a specific object, sometimes
accompanied by a hand-drawing or an astro-photo. The position of some deep sky objects discovered hundreds
of years ago by astronomers need to be confirmed.
Deep Sky lists are your best reference source when deciding on which deep sky objects to look at. Simply
working of a sky map is fun, but working through a list or catalogue is where your hobby gets serious. Lists
include for example the Messier list of 110 objects, the Lacaille list, the ASSA Top 100 list, your astronomy
club’s list, or even your own list that you compiled yourself!
The best way to start with deep sky objects is by picking up a binocular and searching for the brighter
objects. Not only will you become accustomed to navigating the night sky, you will also make up your mind on
whether you would like to pursue the hobby further and maybe obtain a telescope.
Deep Sky Objects visible with amateur equipment:
-
Open star clusters
Globular star clusters
Nebulae
Galaxies
•
Open Star Clusters. These objects are groups of stars that usually formed in the same nebulous
gas cloud in space. They are also considered to be the younger type of stars. Open star clusters consist
of tens to hundreds of members. So far, over 1,100 of them have been discovered in our Milky Way
galaxy, but there is probably 10 times more.
•
Globular Star Clusters. The other type of star cluster is known as Globular Star Clusters. They can
have hundreds of thousands of member stars. They make fine telescope objects and sometimes a
challenge to hunt! So far, almost 150 of these clusters have been discovered in the Milky Way galaxy.
They contain old stars and many mysteries still surround these strange objects, especially regarding
their formation and distribution.
•
Nebulae. The word nebula means "cloud" or "mist" in Latin. In ancient times people looked up at the
sky without knowing that these 'patches' were actually giant gas clouds in space. They consist of
interstellar matter - more than 90% hydrogen, some helium, oxygen and other elements. Our galaxy is
filled with nebulae - exquisite views through telescopes. Most nebulae are lit up by stars within them,
making it visible to see. The most massive nebulae do not shine at all: they can only be “seen” when
they block the light from stars behind them (these are called dark nebulae). There are 5 main types of
nebulae: reflection, emission, dark, planetary and supernova remnant.
•
Galaxies are the islands of visible matter in the Universe. They can consist of billions or even trillions of
stars and come in many shapes and sizes. Astronomers categorize them as mainly spiral, elliptical or
irregular. The Milky Way galaxy, our "home" in the Universe, is a spiral galaxy. There are numerous
galaxies visible even through amateur telescopes. M31 (Andromeda galaxy) is a perfect example.
Almost all the deep sky objects that you can see, except for galaxies, are located in our Milky Way galaxy.
Buyer beware! If you look at Omega Centauri through a 4 inch telescope, don’t expect to see the same as
through an 8 inch. You only create false expectations if you think a small telescope can do what a larger one
can. The minimum recommend size for a telescope is an 8 inch. BUT: beware of the HST-Syndrome (Hubble
Space Telescope Syndrome): you always want to own a bigger and bigger telescope, in order to see more and
more detail. Bottom-line is that if you do own the Hubble Space Telescope one day, you will want to buy
yourself an even bigger one. Don’t spoil astronomy for yourself by thinking that you cannot do much with
an 8 inch telescope, or even with a binocular. It’s about the passion and appreciation that you acquire for
the objects you see and NOT about the instrument!
Course material for Sky Watching beginners | © ASSA Bloemfontein 2007 | www.assabfn.co.za | [email protected]
11
Telescopes
The Basics of Telescopes
a) Refractors
The refractor telescope uses a lens. Light passes through the lens situated at the front of the telescope and is
focused towards the eyepiece. They are much longer compared to reflectors of similar aperture. The smaller
refractors are compact though, and for deep sky work, refractors are usually better compared to their reflecting
counterparts. They are more expensive though and the larger refractor’s length necessitates an observatory.
b) Reflectors
Reflectors usually use a concave parabolic primary mirror to collect and focus the incoming light back onto a flat
secondary (diagonal) mirror. The secondary in turn, reflects the light out to an opening at the side of the main
tube or through a hole in the primary - and into the eyepiece.
There are various types of reflectors. Newtonians and Cassegrains are illustrated here.
The Newtonian reflector (below) reflects light off the primary mirror, focuses onto the secondary mirror which
further focuses it towards the eyepiece at the SIDE of the telescope. This is the easiest telescope configuration
to build yourself and this usually comes with a Dobsonian mounting.
The Cassegrain reflector (below) reflects light off the primary mirror, focuses onto the secondary mirror which
further focuses it towards the eyepiece at the BOTTOM of the telescope. This configuration saves on size, as you
can increase the focal length of the instrument without physically lengthening the telescope.
Course material for Sky Watching beginners | © ASSA Bloemfontein 2007 | www.assabfn.co.za | [email protected]
12
… Telescopes: Focal length, f-ratio and magnification
The focal length of a telescope is the distance from the primary mirror (or objective lens, for refractors) to the focal point
(which is also called the prime focus). The focal point is where the light rays converge.
The aperture (diameter) of a telescope is the diameter of its lens or mirror (e.g. 8 inch or 12 inch).
The f-ratio is the focal length divided by the aperture of the telescope.
Magnification is the focal length of the telescope divided by the focal length of the eyepiece. The latter is usually displayed
on the eyepiece itself.
Example: To find the f-ratio of a telescope 8 inch (20 cm) in diameter with a 1 meter (100 cm) focal length:
Divide 100 cm focus length (FL) by 20 cm diameter (D) to get an f-ratio of 5. To calculate the magnification:
1000 mm (100 cm) focal length divided by 35 mm eyepiece focal length equals 28 times magnification.
What telescope to buy?
It is imperative to buy the best telescope for your budget and your specific needs. The general rule of thumb with a telescope
is “the bigger the better”. When we talk about how big a telescope is, remember that we are talking about the diameter of its
lens or mirror (e.g. 8 inch or 12 inch) and NOT about the length of its tube!
If you’re not going to build your own telescope and want to buy one, but you don’t have at least R4 000 to spend, then save a
bit more! It is recommended that you start with at least an 8 inch reflecting telescope. A 6 inch refractor with good
optics might also be sufficient. Less than 8 inch and you will soon loose interest in astronomy, especially if you’re not
experienced in telescope operations. It is only through an 8 inch and up that the individual stars of a globular cluster are
resolved while still using an acceptable field of view and optical quality.
If you have R20 000 to spend on an 8 inch telescope, then only spend it if you know you’re going to use the telescope and all
its add-ons often. So many expensive telescopes become nothing more than a 2nd hand classified ads because the owner
either does not have time to use it or is just to lazy to learn how to properly operate it! Keep in mind that the QUALITY of an
8 inch telescope with a price of R4 000 might be BETTER than the quality of an 8 inch telescope that costs R20 000. The more
expensive telescope comes with fancy add-ons like the go-to function and a motorized drive, but pay for it only if you are
really going to use it!
Word of warning: a cheap department-store telescope will do more harm to your interest in astronomy than good.
What telescope to build?
Building a telescope is not only very satisfying, but also a great learning experience. Some amateurs, after they’ve built their
first telescope, loose interest in everything else about astronomy except building telescopes!
Building a telescope is not difficult, but it takes time. A beginner might grind and polish an 8 inch mirror for 20 to 40 hours.
The rest of the telescope can be constructed in a weekend. After your first telescope, you soon become adept at grinding and
polishing and it goes much quicker second time round.
Telescopes (commercial and self-built) is decreasing in price, due to mass production. You can now build a decent 8 inch, with
an eyepiece included, for less than R2 000. As soon as you go above an 8 inch, the price will rise proportionally. Start off with
nothing more than an 8 inch – the chances of failure are high. You don’t want to waste a precious 11 or 14 inch mirror your
first time as the glass is expensive and hard to come by.
And note: a self-made telescope can in certain cases be just as good as a commercially bought telescope of the same aperture
or EVEN BETTER. It is not uncommon to hear of an 8 inch telescope that were self-made for R2000 outperforming the optics
of a commercial 8 inch that cost the buyer R20 000. Contact your nearest ASSA Centre for advice in self-made telescopes.
Using Binoculars for astronomy
It is important not to underestimate the value of binoculars when it comes to night sky observations. In fact, an amateur
should try to master a binocular first before moving on to a telescope. If you cannot navigate with a binocular, chances
are that you won’t be able to manage a manual telescope.
The minimum recommended size of a binocular for astronomy is a 10x50. The 10 refers to the magnification and the 50 to
the diameter of the lenses at the front. Some amateurs prefer a 12x50 – the difference between that and a 10x50 is quite
evident. Larger than 12x50 and your binocular becomes heavy and thus shaky – for a binocular of size 16x80, you will most
probably need a tripod (or a very steady hand!) If you think you’re going to make astronomy your hobby, invest in a quality
binocular; you won’t be sorry. A good binocular is an investment worth making, even if you have a telescope.
Course material for Sky Watching beginners | © ASSA Bloemfontein 2007 | www.assabfn.co.za | [email protected]
13
6. Workshop in Night Sky Observations
6.1 Using a sky map to find stars and deep sky objects
Sky maps: what is it used for?
Without proper sky maps, your interest in night sky observations will fade like a comet on its return path to the
Oort Cloud. Be sure to get yourself some decent sky maps (some are supplied with this course): they can be
found in quality books, through software on the internet, or through atlasses that you can buy. When doing
visual observations, sky maps are used to identify and study constellations and stars, finding the positions of
deep sky objects and much else. A too-detailed star atlas won’t assist a beginner, but a cheap sky map you
downloaded from the internet may also harm your interest.
What sky map to use?
The sky map that you choose will be determined by the season; Summer, Autumn, Winter and Spring. Some
observers work through a constellation in a certain month and see how many deep sky objects in it they can
find below a certain magnitude. Many books have a sky map for each constellation.
Orientation with a sky map
You’re all set: equipment in hand, flashlight charged, sky map at the ready. What now? First you should orient
yourself with your aky map. Make sure you know where the wind directions are – e.g. north, south, east and
west. You will also have to know how to interpret the scale of the star chart, otherwise you will be forever lost…
The constellations look MUCH smaller on the paper than in the sky! Get to grips with the scale first-thing.
Unaided eye, binoculars, telescope observations
a) Unaided eye observations and sky maps
Too many people make the mistake of thinking that you can only do sky watching and astronomy if you own a
telescope. What absolute rubbish! The unaided eye is the easiest way to start by far! Develop a feel for the
positions of the constellations and stars before moving on to any instruments. Select a bright star or
constellation on the sky map and search for it in the sky. Your head will bob up and down until you want to
scream, but that’s the only way to learn. Then star hop to the next brightest star. Star-hopping is one of the
best ways to learn the constellations from a map. Come back a few evenings later and recap what you’ve seen.
b) Binocular observations and sky maps
After you’ve learned the positions of a few constellations and stars with the unaided eye, you can attempt some
binocular observations. The first evening that you take your binocular outside, put aside your sky map! Simply
scan the skies with your binocular, especially within the region of the milky way, and see how many strangelooking objects there are! THAT’S when one’s interest really start to take off in astronomy... After you have
tickled your interest and you are simply burning to know what those mysterious objects are, try to find them on
the sky map.
c) Telescope observations and sky maps
What about those really faint little fuzzies that are so elusive that you search for them many minutes on end?
The detail of your sky map will play a role in how easy you find them and will also assist you in star-hopping by
using your finderscope. You should try to become accustomed to the operations of your telescope: if you move
the telescope to the right, what happens with the image in the eyepiece? Does your eyepiece flip and/or mirror
the image? Know your telescope: practice, practice, practice...
What is “deep sky lists”?
A deep sky list is a specific catalogue of objects either compiled by a noted astronomer in the past or an official
governing body. The most famous deep sky list is no doubt the Messier catalogue, containing 110 deep sky
objects. Charles Messier compiled this list in the 1700’s. It contains mostly bright deep sky objects either visible
through a binocular or small to medium-sized telescopes. This list is good for beginners to commence their
deep sky careers in! Another interesting list was compiled by the Frenchman Nicolas Louis de Lacaille while at
the Cape, also in the 1700’s, containing 42 objects in mostly the southern regions of the sky. It contains some
of the most beautiful objects in the sky.
You can even create your own list! ASSA Bloemfontein has for instance, a handy binocular list with some of
the best binocular objects in the sky. ASSA National has a superb list, called the “ASSA Top 100”, containing the
best objects visible from our southern skies for telescopes. These lists are on your Astronomy CD.
Course material for Sky Watching beginners | © ASSA Bloemfontein 2007 | www.assabfn.co.za | [email protected]
14
6.2 Using a planisphere for orientation
See the planisphere that came with your course material. It indicates all the constellations, visible throughout
the year. The major star names also appear thereon.
What is a planisphere used for?
A planisphere is an excellent aid to help you get orientated with the night sky before doing sky watching. It
enables you to have a quick look at which constellations and stars are currently visible in the night sky. It also
shows you the rise and set times of the constellations as well as which constellations are crossing the meridian
at any given time (the meridian is the line running from north to south through our zenith directly above you).
A planisphere cannot replace a sky map and you cannot necessarily study the constellations from it. It’s not
suitable for deep sky objects at all. It only gives the broader picture. Keep it near to your desk or computer at
all times and make sure you always carry it with you when you go out to watch the stars.
A few questions relating to planispheres
1.
Move the planisphere to April 22, 20h00 in the evening.
What is the name of the most northern constellation on the planisphere?
What constellation is rising on the north-eastern horizon?
What constellation on the northern horizon is going to set completely within 2 and a half hours?
What very bright northern-most star would just have risen after midnight?
How late does the star Regulus in Leo set?
2.1
2.2
Name 1 circumpolar constellation that is visible throughout the year (never sets)
What 3 months of the year are the worst for observing Crux around midnight?
3.1
Move the planisphere’s disk to display the stars visible on 30 June at 20h00: how late will the
constellation of Cygnus be fully visible? (north-east horizon)
What constellation containing a well known red giant star is on your meridian (and close to your
zenith to) at 19h00 on August 15?
What very large northern constellation closest to the horizon culminates at 20h00 on November 10?
(tip: it has a big square)
3.2
3.3
Answers:
1.1) Leo Minor 1.2) Bootes 1.3) Gemini 1.4) Vega 1.5) About 1h15 2.1) Apus, Musca, Octans 2.2) August to October
3.1) 22h00 3.2) Antares in Scorpio 3.3) Pegasus
6.3 Using software to plan your observing sessions
Programs you can use to find the positions of the moon, planets, constellations and stars with:
-
Stellarium: An excellent planetarium application. Not for serious deep sky or printing of sky maps, but a
great tool to see what stars and constellations will be visible, what planets are in the sky and where
the Moon is situated. Go to www.stellarium.org: freeware
Starry Night: A comprehensive commercial package. You can print sky maps from it too.
The following software packages are available to generate detailed star charts with for the serious observer:
-
Skymap: commercial, but version 8’s demo is free and can be found on the club CD - www.skymap.com
The Sky: commercial package: www.bisque.com
Cartes du Ciel: freeware. Comprehensive, but takes some to learn: www.stargazing.net/astropc and
needs several additional file-download to make it work properly.
Other software includes Celestia, a solar system and deep space simulator. Virtual Moon Atlas can be used
to explore the service of the Moon in increcible detail. Registax is used by Astrophotographers to stack their
photos and develop stunning photography in the process.
Course material for Sky Watching beginners | © ASSA Bloemfontein 2007 | www.assabfn.co.za | [email protected]
15
7. Preparing for Night Sky Observations
For basic Night Sky observing, you will need the following tools and instruments:
•
Your Eyes
On any given dark night, there are several deep sky objects visible with the unaided eye. They consist mostly of
open clusters (e.g. the M45 cluster called the Seven Sisters, the M7 open cluster in Scorpius, the large Coma
Berenices and Hyades star clusters etc). Some nebulae are also visible (e.g. the Orion, Tarantula and Lagoon
nebulae). Galaxies visible include the Large and Small Magellanic clouds and the Andromeda galaxy.
•
Binocular
Many people underestimate the power and functionality of binoculars for night sky
observations. They are truly excellent optical instruments to start deep sky
observing with. In fact, many an amateur astronomer carries his binocular around
his neck, even when he stand next to a large telescope! Literally dozens of deep
sky objects and beautiful star fields are easily visible with binoculars. It will also
assist you in finding objects faster with your telescope.
•
Telescope
For the serious night sky observer, a telescope will be a welcome addition to
the inventory. In fact, for sustained interest in the hobby of Deep Sky
observing, it may become essential. It is not necessary to start off with a
telescope – many people make the mistake that a telescope will magically teach
them all there is to know about science and life itself. But remember: you will
ALWAYS want a larger telescope, even if you own the Hubble itself. You must
make the best of your limited resources and develop a passion for your interest
in astronomy by knowing what you are looking at and realizing the inner
splendour of the object and the “physics” involved. Be sure to talk to an
experienced telescope owner before you decide to build or buy a telescope.
•
Red filtered flashlight
Without a red-filtered flashlight, your eyes will never be able to work in a dark adapted environment – essential
for effective observations. Any flashlight you buy in the shop can be filtered with red iced paper or other red
see-through material. Try to buy rechargeable batteries and a charger, it will save you lots of money and
trouble! You received some red filter paper with your course material.
•
Sky maps
Without the right kind of sky map, you will quickly loose interest in observations and may even become
frustrated. Books in the shops frequently have star charts in, but are not always detailed enough. Goods star
charts can be found in software programs like Skymap, Cartes du Ciel and The Sky. Printed star atlases like
the Uranometria, Norton’s and the Millennium Star Atlas are top of the crown, but is recommended for
advanced observers only.
•
Pencil & Notebook, Drawing sheet and Report log
These items are necessary when you start logging your observations or when you start drawing objects and
report on its characteristics.
•
Physical Environment: comfort and practicality
Observing Deep Sky objects is NOT for the faint hearted. It takes effort, time and dedication. So, make sure
your physical environment is as comfortable as possible.
Dress for cold: cover your head, neck, nose & ears and wear a jacket and appropriate trousers (jeans are not
good insulators of heat and will let you quickly run inside to comforting glare of that beloved family TV).
Sit comfortably: Make sure your writing area is convenient and stable. Be sure to have ALL your equipment
within reach and at the ready. And most importantly: have some snacks during the observation. It is suppose to
be FUN!!
Course material for Sky Watching beginners | © ASSA Bloemfontein 2007 | www.assabfn.co.za | [email protected]
16
Appendix A – List of the brightest and nearest stars
List of Brightest Stars
List of Nearest Stars
The Brightest Stars, as seen from the Earth:
Rank
Common Name
Scientific Name
Sun
Distance
(light years)
Apparent
Magnitude
This list of the Nearest Stars to Earth is
ordered by increasing distance:
Star name
Distance from Earth
-
-26.7
1
Sirius
Alpha CMa
8.6
-1.4
1
Sun
2
Canopus
Alpha Car
74
-0.7
2
Alpha Centauri Star System
3
Rigil Kentaurus
Alpha Cen
4.3
-0.2
Proxima Centauri
4.2 light years
4
Arcturus
Alpha Boo
34
0
Alpha Centauri A
4.3
5
Vega
Alpha Lyr
25
0
Alpha Centauri B
4.3
6
Capella
Alpha Aur
41
0
3
Barnard's Star
5.9
7
Rigel
Beta Ori
773
0.1
4
HPMS
7.5
8
Procyon
Alpha CMi
11.4
0.3
5
Wolf 359
7.7
9
Achernar
Alpha Eri
69
0.4
6
Lalande 21185
8.2
7
Sirius Star System
8 light minutes
10
Betelgeuse
Alpha Ori
427
0.5
11
Hadar
Beta Cen
320
0.6
12
Acrux
Alpha Cru
510
0.7
8
UV Ceti Star System
8.7
13
Altair
Alpha Aql
16
0.7
9
Ross 154
9.6
Sirius A, Sirius B
8.5
14
Aldebaran
Alpha Tau
60
0.8
10
Ross 248
10.3
15
Antares
Alpha Sco
605
0.9
11
Epsilon Eridani
10.5
16
Spica
Alpha Vir
220
0.9
12
Lacaille 9352
10.7
17
Pollux
Beta Gem
40
1.1
13
Ross 128
10.9
18
Fomalhaut
Alpha PsA
22
1.1
14
EZ Aquarii Star System
11.2
19
Becrux
Beta Cru
460
1.2
15
Procyon Star System
11
20
Deneb
Alpha Cyg
2600-3300
1.2
16
61 Cygni Star System
11
21
Regulus
Alpha Leo
22
Adhara
Epsilon CMa
69
1.3
17
GI 725 Star System
11.5
570
1.5
18
GI 15 Star System
11.6
23
Castor
24
Gacrux
Alpha Gem
49
1.5
19
Epsilon Indi
11.8
Gamma Cru
120
1.6
20
DX Cancri
11.8
25
Shaula
Lambda Sco
330
1.6
21
Tau Ceti
11.8
22
GJ 1061
11.9
23
YZ Ceti
12.1
24
Luyten's Star
12.3
25
Kapteyn's Star
12.7
Appendix B: Binoculars Deep Sky List per season
All these objects can be found on the sky maps included in your course material
Summer skies (December to February)
Notes
1. M41 – Large Open Cluster in Canis Major (faintly visible with naked eye) Mag 4.5, Size 38.0'
2. M42 – Nebula in Orion (faintly visible with naked eye). Mag 4.0, Size 90.0'x60.0'
3. M35 – Open cluster in Gemini – easily visible in binoculars. Mag: 5.1, Size 28'
4. M44 – Large open cluster in Cancer (Beehive cluster) – Visible with eye as a faint fuzzy cloud, Mag: 3.1,
Size: 95.0'
5. Large and Small Magellanic Clouds – the perfect time of the year! While you’re looking at them, try to see the
Tarantula nebula (NGC 2070) in the LMC and Tucana 47 (NGC 104) close to the SMC.
Autumn skies (March to May)
1. Coma Berenices Star Cluster (naked eye/binocular wide field, 37 cluster members).
2. IC 2602 – Open cluster in Carina (Southern Pleiades) Magnitude: 1.9, Size: 100.0’
3. NGC 3532 – Open Cluster in Carina (Wishing well cluster) Magnitude: 3.0, Size: 50.0’
4. NGC 3372 – Nebula in Carina (Keyhole nebula) Magnitude: 3.0, Size: 120.0’
5. NGC 5139 – Globular cluster in Centaurus (Omega Centauri) Magnitude: 3.7, Size: 36.3’
Winter skies (June to August)
1. M8 – Bright Nebula in Sagittarius (Lagoon) – Eye/Binocular. Mag: 5.0, Size 45.0’x30.0’
2. M20 – Bright Nebula in Sagittarius (Triffid) – Strong binocular, Small tel. Mag: 6.3, Size: 28.0’
3. M22 – Globular cluster in Sagittarius – looks like small fuzzy cloud! Mag: 5.1, Size: 17’
4. M6 – Open cluster beneath tail of Scorpius – Seen with unaided eye. Mag: 4, Size: 20’
5. M7 – Open cluster beneath tail of Scorpius – Seen clearly with unaided eye. Mag: 3, Size: 80’
6. NGC 6231 star region – Open cluster in star-rich area, start of Scorpios’ tail. Mag: 2, Size: 15’
7. The Milky Way in winter – one of the most stunning sights for a binocular. Scan the Scorpius/Sagittarius
area of the sky: you’ll be surprised with all the deep sky treasures…
Spring skies (September to November)
1. M10 – Globular Cluster in Ophiuchus (strong binocular, medium telescope). Mag 6.7, Size 12.2’
2. M12 – Globular Cluster in Ophiuchus (strong binocular, medium telescope). Mag 6.6, Size 12.2’
3. M31 – Andromeda Galaxy (visible even with unaided eye dark nights). Mag 4.3, Size: 189.1’x61.7’
4. M45 – Pleiades star cluster in Taurus (group of stars visible with unaided eyes, stunning through binoculars).
5. Hyades star cluster – very large open cluster only visible with unaided eye in Taurus
Visit ASSA Bloemfontein’s website and go to the Deep Sky pages for a comprehensive list of binocular
objects per constellation – www.assabfn.co.za/deepsky.htm
Appendix C: List of the 88 official constellations
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
Abbrev
And
Ant
Aps
Aqr
Aql
Ara
Ari
Aur
Boo
Cae
Cam
Cnc
CVn
CMa
CMi
Cap
Car
Cas
Cen
Cep
Cet
Cha
Cir
Col
Com
CrA
CrB
Crv
Crt
Cru
Cyg
Del
Dor
Dra
Equ
Eri
For
Gem
Gru
Her
Hor
Hya
Hyi
Ind
Lac
Leo
Constellation
Andromeda
Antlia
Apus
Aquarius
Aquila
Ara
Aries
Auriga
Bootes
Caelum
Camelopardalis
Cancer
Canes Venatici
Canis Major
Canis Minor
Capricornus
Carina
Cassiopeia
Centaurus
Cepheus
Cetus
Chamaleon
Circinus
Columba
Coma Berenices
Corona Australis
Corona Borealis
Corvus
Crater
Crux
Cygnus
Delphinus
Dorado
Draco
Equuleus
Eridanus
Fornax
Gemini
Grus
Hercules
Horologium
Hydra
Hydrus
Indus
Lacerta
Leo
Latin
Andromedae
Antliae
Apodis
Aquarii
Aquilae
Arae
Arietis
Aurigae
Bootis
Caeli
Camelopardalis
Cancri
Canun Venaticorum
Canis Majoris
Canis Minoris
Capricorni
Carinae
Cassiopeiae
Centauri
Cephei
Ceti
Chamaleontis
Circini
Columbae
Comae Berenices
Coronae Australis
Coronae Borealis
Corvi
Crateris
Crucis
Cygni
Delphini
Doradus
Draconis
Equulei
Eridani
Fornacis
Geminorum
Gruis
Herculis
Horologii
Hydrae
Hydri
Indi
Lacertae
Leonis
Proper Name
Princess Andromeda
Air Pump
Bird of Paradise
Water Carrier
Eagle
Altar
Ram
Charioteer
Herdsman
Chisel
Giraffe
Crab
Hunting Dogs
Big Dog
Little Dog
Goat (Capricorn)
Keel of Argo
Queen Cassiopeia
Centaur
King Cepheus
Whale
Chameleon
Compasses
Dove
Berenice's Hair
Southern Crown
Northern Crown
Crow
Cup
Southern Cross
Swan
Dolphin
Swordfish
Dragon
Little Horse
River
Furnace
Twins
Crane bird
Hercules the Hero
Clock
Hydra (Sea Serpent)
Water Serpent
Indian
Lizard
Lion
Notes
...list of the 88 official constellations continued
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49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
LMi
Lep
Lib
Lup
Lyn
Lyr
Men
Mic
Mon
Mus
Nor
Oct
Oph
Ori
Pav
Peg
Per
Phe
Pic
Psc
PsA
Pup
Pyx
Ret
Sge
Sgr
Sco
Scl
Sct
Ser
Sex
Tau
Tel
Tri
TrA
Tuc
UMa
UMi
Vel
Vir
Vol
Vul
Leo Minor
Lepus
Libra
Lupus
Lynx
Lyra
Mensa
Microscopium
Monoceros
Musca
Norma
Octans
Ophiucus
Orion
Pavo
Pegasus
Perseus
Phoenix
Pictor
Pisces
Pisces Austrinus
Puppis
Pyxis
Reticulum
Sagitta
Sagittarius
Scorpius
Sculptor
Scutum
Serpens
Sextans
Taurus
Telescopium
Triangulum
Triangulum Australe
Tucana
Ursa Major
Ursa Minor
Vela
Virgo
Volans
Vulpecula
Leonis Minoris
Leporis
Librae
Lupi
Lyncis
Lyrae
Mensae
Microscopii
Monocerotis
Muscae
Normae
Octantis
Ophiuchi
Orionis
Pavonis
Pegasi
Persei
Phoenicis
Pictoris
Piscium
Pisces Austrini
Puppis
Pyxidis
Reticuli
Sagittae
Sagittarii
Scorpii
Sculptoris
Scuti
Serpentis
Sextantis
Tauri
Telescopii
Trianguli
Trianguli Australis
Tucanae
Ursae Majoris
Ursae Minoris
Velorum
Virginis
Volantis
Vulpeculae
Little Lion
Hare
Balance (Scales)
Wolf
Lynx
Lyre (Harp)
Table Mountain
Microscope
Unicorn
Fly
Square
Octant
Serpent Carrier
Orion the Hunter
Peacock
Winged Horse
Perseus
Phoenix
Easel
Fishes
Southern Fish
Stern of Argo
Compass of Argo
Reticle or Net
Arrow
Archer
Scorpion
Sculptor
Shield
Serpent
Sextant
Bull
Telescope
Triangle
Southern Triangle
Toucan bird
Great Bear
Little Bear
Sails of Argo
Virgin
Flying Fish
Fox
Star Gazing facts and figures
a) The milky way
- The milky way is an arm of our spiral galaxy and appears so bright because of the numerous stars within the arms.
- The dark patches inside the milky way consist of cosmic dust and gas, which obscures the light from the stars in the
background. One example of such a dark patch is the “Coal Sack nebula” visible below the Southern Cross.
- When you look to the milky way in winter in the direction of the constellation of Sagittarius, you are in fact looking towards the
centre of our Galaxy.
b) How many stars?
- During a dark night you can see between 2 000 and 3 000 stars with your naked eye. There are however, an estimated
200 billion stars in our Galaxy alone!
- All the stars that you can see with your unaided eyes are situated in our Galaxy. There are only three objects outside that are
visible with the unaided eye: the Small Magellanic and Large Magellanic Clouds in the south, which are both satellite galaxies of
our own, and the Andromeda Galaxy above the northern horizon in spring, the closest large spiral galaxy to ours.
c) How many constellations?
- There are 88 constellations in the whole of the sky. We can see almost 80 of them from Southern Africa.
- The constellations to the north were mostly invented by ancient cultures such as the Greeks and Romans, but the
constellations to the far south were invented by European seafarers sailing into the southern hemisphere and by astronomers
who visited the Cape in the 1700’s.
d) Distances and light years
The distance to stars is measured in light years. One light year is the distance that light travels in 1 year, at 300 000 km/s! This is
as fast as going around the Earth 7 times in only 1 second. The stars of Alpha Centauri, which is 4.3 light years from us, is the
closest solar system to our own solar system. This means that it takes light just over 4 years to travel between Alpha Centauri
and your eyes... If Alpha Centauri were to explode today, you will only see the explosion in 4 years’ time...
When you look up at the stars, it is almost as if you are “looking back in time”.
The Sun
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The distance from the Earth to the Sun is 150 million km on average
The Sun is about 1.4 million km in diameter (the Earth’s is 12 756 km). Almost 110 Earths can fit into the Sun’s diameter.
It takes light waves 8 minutes to travel between the Sun and Earth
The Sun contains 99.8% of the mass of the solar system
At the equator, it takes the Sun 25 days to make one rotation around its own axis.
Each second about 700 million tons of hydrogen is converted into 695 million tons of helium.
The Sun’s surface temperature is 5,500º C and at the core it is 15 millionº C.
The Moon
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The diameter of the Moon is 3 476 km and that of the Earth 12 756 km
The Moon is on average 380 000 km from the Earth
There were in total 6 human landings on the Moon during the Apollo missions, from 1969 to 1972.
With Apollo 11, Neil Armstrong becomes the first man to walk on the Moon.
A total of 382 kg of lunar rocks were brought back from the Moon from all missions.
The Moon has no atmosphere and virtually no geological activity.
The Moon might have either formed from the same dust disk from which Earth formed, or it might have been part of the
forming Earth (torn away by a collision).
The Planets
Distances from the Sun
Planet
Diameter
Mercury
4,880 km
Venus
12,104 km
Earth
12,756 km
Mars
6,794 km
Jupiter
143,884 km
Saturn
120,536 km
Uranus
51,118 km
Neptune
50,538 km
Distance from Sun
58 million km (0.4 AU)
108 million km (0.7 AU)
150 million km (1 AU)
228 million km (1.5 AU)
780 million km (5.2 AU)
1430 million km (9.5 AU)
2870 million km (19.2 AU)
4500 million km (30 AU)
Mythological character
Hermes, messenger of the gods
Roman goddess of beauty and love
Your home in the solar system…
The god of War
Supreme diety of the Romans
The god of harvest
The god of the sky
The god of water
Dwarf planet Pluto
Pluto
2324
6000 million km (40 AU)
Also called Hades, god of the underworld
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Astronomy facts and figures
Comparisons
Earth’s size: 11 Earths can fit into the diameter of Jupiter while 10 Jupiters, or 110 Earths, can fit into the diameter of our Sun!
Size of the Sun and distance to Alpha Centauri: If the Sun were the size of an aspirin, our nearest star Alpha Centauri would
have been another aspirin 140 km away! *
Distance to Pluto: It will take the New Horizon’s probe almost 10 years to travel between the Earth and Pluto (NASA-JPL).
Atoms and molecules: If you take a deep breath, there will be more air molecules in your lungs than there are stars in all the
galaxies in the whole of the visible Universe put together. *
Number of stars and distance between stars: If each star were represented by a single grain of rice, a scale model of the
Milky Way Galaxy would just fit into the gap between the Earth and the Moon. *
Black holes: If you could squeeze the Earth into the size of a pea, it would become a black hole!
Light years: The nearest star to our Sun is called Alpha Centauri. It is 4.3 light years distant. This means that it takes light just
over 4 years to travel between Alpha Centauri and our Sun. You see Alpha Centauri as it appeared 4 years ago. If it were to
explode today, you will only see the explosion in 4 years’ time.
Speed of light: Light waves travel at 300 000 km/s. This is as fast as 7 times around the Earth in one second!
Some more facts:
What is a “shooting star?” A shooting star is simply a small piece of dust or sand entering the Earth’s atmosphere. It then
travels at an immense speed as it is pulled towards the Earth due to gravity. Ram pressure builds up in front of the little particle,
creating extreme heat. The atmosphere around the particle catches fire, which in turn ignites the particle. It then “burns” up,
emitting huge quantities of energy: seen as a streak of light from Earth. These particles can travel at a speed of 70 km/s and
burns up a few dozen km above the surface. If it doesn’t burn up completely, it leaves a meteorite. Some are miniscule, others
large enough to pick up (or cause serious damage). Scientists estimate that 1,000 tons to 10,000 tons of meteoritic material falls
on the Earth each day.
Why isn’t Pluto a planet anymore? Astronomers have invented a definition for “planet” in August 2006 and Pluto does not
adhere to the criteria of this definition. Pluto is now called a “Dwarf Planet”.
Have they ever sent people to other planets? No. The furthest that humans have ever gone is the Moon. NASA plans to
return astronauts to the moon by 2020. The first people may land on Mars by 2030. All the 8 planets however, has been visited
by unmanned satellites and a probe is on its way to Pluto to arrive there in 2015.
What is the “morning and evening star”? It is not a star at al! It is the planet Venus: one and the same thing. Sometimes
visible in the evenings, other times of the year visible in the morning sky.
What happens when a star dies? Most stars swell up to become red giants when they near the end of their lives. They become
much bigger than they were and turn red. Our Sun’s hydrogen supplies will run out in about 5 billion years’ time when it too will
swell up and form a red giant. It will shed its outer gas layers to form a planetary nebula. A white dwarf star, as big as the Earth
but MUCH heavier, will remain. Stars much heavier than our Sun may explode in a supernova and form a neutron star or black
hole. Our Sun is not massive enough to become a neutron star or black hole. And remember that it’s not about the size, it’s
about the mass!
What is a black hole? Black holes are the highly compressed "remnants" of extremely massive stars and is
packed with so much matter that it creates a huge gravitational pull on anything coming too close. It is thus the remains of a
dead star which was very heavy during its life. Only massive stars can become black holes. Stars with a mass of over 8 to 10
times the mass of the Sun can explode as supernovas and might eventually become black holes (or neutron stars if it is not
massive enough). It appears as if most galaxies have supermassive black holes at their centre, including ours. It will only
consume you if you come within a certain distance of it, or within its event horizon.
* From the book “Hyperspace”, but John Gribbin.
Compiled by ASSA Bloemfontein Centre, 2007.
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