Download Legends, Art, and Science: Practical Astronomy for your Nightly Life

Legends, Art, and Science: Practical
Astronomy for your Nightly Life
Week Two: Stars and Constellations
Instructor: Robert Arn
Website: www.astroarn.com
Email: [email protected]
Course: #Oshr 1507 100
Brightness of Stars
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Objects in space have two descriptors for brightness of an object - apparent
magnitude and absolute magnitude.
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Absolute magnitude describes the brightness of an object as if it were viewed
from a position 32.6 lightyears (10 parsecs) away.
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Apparent Magnitude is the brightness of an object as seen from Earth
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The small the number, the brighter the object.
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Each magnitude scales by ~2.5 times dimmer
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Example: A star that is mag 3 is 2.5 times dimmer than a star of mag 2.
Refers to
Apparent
Stellar
Magnitude
-26.74
Sun (400,000 times brighter than Full Moon)
-12.92
Full Moon
-9.5
Maximum Brightness of Iridium Flare
-4.89
Maximum Brightness of Venus
-4.00
Faintest object observable during day
-3.8
Maximum Brightness of Venus
-2.9
Maximum Brightness of Jupiter
-1.47
Brightest Star: Sirius
-0.72
Second Brightest Star: Canopus
0.03
Vega
3.44
Andromeda Galaxy (M31)
6.50
Limit of stars observed with naked eye
31.50
Faintest Objects Observed with Hubble
36.00
Faintest Objects Predicted with E-ELT (2020)
Circumpolar Stars
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If you are anywhere on Earth except
the equator you can always see a
certain collection of stars - no matter
what time of year it is.
These are called Circumpolar stars
and they surround the North
Celestial Pole (Polaris)
All stars whose diurnal path
crosses this line are circumpolar
from ~38˚ N Latitude
Astronomy Weather
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Before going out to a dark site to enjoy the night sky, there are a few weather
conditions, unique to astronomy that you might want to check first.
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Cloud Cover: This one is obvious. If there are clouds in the sky, you are
not going to see much.
Transparency: Refers to the amount of water vapor in Earth’s Atmosphere.
This directly impacts our ability to look at deep sky objects with
binoculars, cameras, or telescopes. Only in severe cases (which are
uncommon but not improbable) can it affect our ability to see objects with
the naked eye.
Seeing: A combination of atmospheric turbulence with the differences in
temperature between various layers of our atmosphere. Poor seeing will
impact our ability to look at objects in the solar system (local objects). And
seeing is also responsible for causing stars to twinkle.
An astronomer’s weather forecast is the 2nd most
accurate weather forecast created. It provides hour by
hour changes in Cloud Cover, Transparency, Seeing,
Wind, Humidity, and Temperature.
The downsides to this type of weather predication are
that the forecast is only good for a particular location
±15 miles and the forecast is only extended ~40
hours in the future.
cleardarksky.com/csk/
Twinkling Stars
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When you are in an outdoor swimming pool in the
middle of the day, you notice that light seems to
“bend” when it reaches the surface of the water
(you can notice this at home with a glass of water
and a light source).
The same effect happens with star light as it moves
through our atmosphere in a phenomena called
Scintillation - and this inspired the tune of
“Twinkle, Twinkle, Little Star”
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The index of refraction is the ratio of the speed of
light in a vacuum to that in some medium. The
closer to a ratio of 1, the less bent light rays
become.
The typical index value of air is 1.000293 meaning that star light bends very slightly from a
straight line.
Our atmosphere is constantly changing.
Turbulence is always presents and fluctuation in
wind speed, temperature, and air density can
change the sky on the order of a few millimeters
to several meters in just a fraction of a second.
When this occurs, the index of refraction changes
very quickly and as the star light enters our eye,
we see the effects of the light bending by
observing different wavelengths of that light
(causing us to see a change in color and intensity)
Betelgeuse
What is a Constellation
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A constellation is a grouping of stars that form a
pattern to an individual.
While there is a commonly accepted set of
constellations, due to an accepted mythology
(northern hemisphere), there is no scientific value
to these groupings.
A fun activity under the night sky is to create your
own constellations!
Birth of Modern Constellations
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While patterns in the sky have been created for
most of human history, the first written record was
in the Mesopotamian culture in 4000B.C.
In the 8th century, a few familiar constellations
appeared in Homer’s epic poem, the Odyssey.
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400 years later Eudoxus of Cnidus wrote about 43
or 45 or 48 constellations (depending on various
interpretations of the text) which we know today.
While Eudoxus work was lost, his ideas were kept
alive by Aratus in a poem called Phaenomena.
For a translation of Phaenomena (with commentary)
check the following books:
Callimachus - Hymns and Epigrams, Lycophron, Aratus, Harvard University Press, Cambridge,
Massachusetts, London, England; 1921, revised 1955. ISBN 0-674-99143-5
Aratus: Phaenomena, Cambridge University Press, Cambridge, Massachusetts, 1997. ISBN 0-521-058230-X
Phaenomena, The Johns Hopkins University Press; 2010. ISBN 0-801-89466-4
The Classical Constellations
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Ptolemy, and Alexandrian astronomer in the 2nd
Century listed 48 constellations in his book,
Almagest.
He used his own observational data collected over
30 years with historical data reaching back to the
8th century B.C.
All of his constellations are still in use today*
21 Northern Constellations
Andromeda, Aquila, Auriga, Boötes, Cassiopeia, Cepheus, Corona Borealis, Cygnus,
Delphinus, Draco, Equuleus, Hercules, Lyra, Ophiuchus, Pegasus, Perseus, Sagitta,
Serpens, Triangulum, Ursa Major, Ursa Minor
12 Zodiacal Constellations
Aries, Aquarius, Cancer, Capricornus, Gemini, Leo, Libra, Pisces, Sagittarius, Scorpius,
Taurus, Virgo
15 Southern Constellations
Ara, Argo Navis, Canis Major, Canis Minor, Centaurus, Cetus, Corona Australis, Corvus,
Crater, Eridanus, Hydra, Lepus, Lupus, Orion, Pisces Austrinus
Argo Navis (the Ship Argo) has been broken up into smaller part, Carina (the Keel),
and Puppis (the Stern).
Modern Constellations
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The Almagest was the official word on constellations for over 1000 years. During
that time there had been slight updates to the magnitude and position of stars,
but no other lasting changes.
In 1536, German globe maker Caspar Vopel added two northern constellations:
Coma Berenices and Antinous (of which only Coma Berenices survives).
The problem with the 48 classical constellations, is that it did not cover the entire
sky. Stars from the southern hemisphere were not viewable from Europe - so no
one came them names!
Southern Constellations
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In 1589, Dutch astronomer Plancius started to create
southern constellations with Crux, and Triangulus
Antarcticus.
Over the next 23 years he added a dozen
constellations, 4 of which are still in use today.
In the 17th century Hevelius added another round of
constellations. Then 64 years later LaCille added
more constellations and broke Argo Navis into 3
parts. These were the last officially recognized
constellations.
Failed Attempts
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Many other astronomers from the 17-19th
centuries tried to add constellations but they were
soon forgotten.
In 1801 Johann Bode published a set of celestial
maps which included 99 constellations.
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This was the last great star atlas to illustrate so
many constellations which included: static
electricity, a hot air ballon, and a cat.
IAU Definition and Classification
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Originally constellations were defined informally, only
giving a rough idea where something was in the night
sky.
As astronomy research quicken in the early 20th
Century, astronomer decided they needed defined
boundaries for an official set of constellations
Eugene Delporte listed the 88 “modern” constellations
to the IAU in 1930. A set of constellations that still
remains today
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All 88 constellations have a common name and a
Latin name: www.iau.org/public/constellations
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Despite having precise boundaries and
spellings, the IAU has not defined a precise
pronunciation of the constellations. As a result,
many astronomy texts will have different
pronunciation guide.
22
22
22
23
23
23
23
00
00
03
03
03
03
02
02
02
02
01
01
01
01
01
01
00
00
00
00
23
23
23
23
57
57
57
15
15
40
40
27
27
41
36
17
15
35
35
03
03
50
50
29
29
14
14
59
59
16
16
41
41
25
25
22.2843|
12.9665|
04.5897|
26.3193|
15.9577|
52.2171|
47.4863|
03.3033|
41.4993|
14.0997|
56.8883|
34.9098|
36.2232|
02.9609|
12.5653|
10.9501|
05.6697|
22.8534|
08.0739|
49.4433|
37.9047|
25.4169|
21.2179|
09.3282|
06.2585|
34.3869|
35.1282|
06.2589|
04.9337|
51.7638|
48.6945|
53.1680298|CAS
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63.6812897|CAS
63.6928787|CAS
66.6928711|CAS
66.6924438|CAS
77.6923447|CAS
77.4163132|CAS
68.4214401|CAS
68.4662857|CAS
57.4684982|CAS
57.5513000|CAS
59.0511551|CAS
59.1046104|CAS
58.1046753|CAS
58.1227188|CAS
54.6228828|CAS
54.6477699|CAS
50.6478767|CAS
50.6632347|CAS
48.6632690|CAS
48.6757393|CAS
46.6757545|CAS
46.6949348|CAS
48.6949348|CAS
48.6929169|CAS
50.6929131|CAS
50.6870193|CAS
53.1870041|CAS
Zodiac
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The Zodiac is a ring of constellations that passes
through the ecliptic - the path that the sun travels
Question: How many Zodiac constellations are
there?
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Answer: 13
Capricornus, Aquarius, Pisces, Aries, Taurus,
Gemini, Cancer, Leo, Virgo, Libra, Scorpius,
Sagittarius, AND Ophiuchus.
For anyone interested in astrology, there are only
12 SIGNS of the zodiac. This is due to a
combination of precisely defining constellation
boundaries in the 20th century and the precession
of Earth over the past 2000 years (when astrology
was invented).
http://www.pxzl.com/the-zodiac/
Aquarius - The Water Carrier - Babylonian Name
In Greek mythology, Aquarius (also known as Ganymede in Roman myth) was a beautiful young boy
whom Zeus brought to Olympus to be the cup bearer of the Gods.
Aries - Ram or Golden Fleece Greek, Babylonian, and Egyptian
In Greek myth, Aries carried
Athamas’s son, Phrixux, and
daughter to Colchis to escape Ino.
When Aries reached Colchis,
Phrixux sacrificed the ram and
humg its fleece in the Ares. This
fleece turned into gold and was
used in the quest of Jason and the
Argonauts.
Cancer - Crab
Juno sent a crab to defeat
Hercules while fighting Hydra.
The crab was crushed by
Hercules, but not before
poisoning the mighty hunter.
Capricorn - Sea Goat
Also known as Amaithes who provided for baby Zeus and Rhea saved him from Cronos.
Gemini - Twin Brothers
The two bright stars Castor
and Pollux are also the
brothers’ names. They were
the brothers of Helen of Troy
and are the protectors of ships
and sailors.
Leo - Lion
Prehistoric
constellation
associated with
royalty. In
Egyptian myth, it
represents the life
giving flood since
the Sun was in this
constellation
during heavy rains.
In Greek myth,
Leo is the lion
which was killed
by Hercules.
Libra - Scales
The only non-living object in
the Zodiac. It is said that
Romans chopped claws from
Scorpio during the Autumn
Equinox to make Libra.
According to the Greeks,
Libra is the scale held by
Astraea that represents
justice.
Ophiuchus - Serpent Holder
In Greek myth, Ophiuchus is
a legendary physician who
tried to become immortal to
avoid death. Zeus killed him
with a bolt of lightening, but
honored him with a place in
the sky because of his good
works.
Pisces - Two Fish
In Roman myth, Venus and her son Cupid escaped Typhon as two fish tied together. In Greek myth,
they are Aphrodite and Eros.
Sagittarius - The Archer
A Chiron, half-man half-horse, sent to kill the scorpion (Scorpio). In Babylonian myth, this represents
the demo Pabilsaq.
Scorpio - The Scorpion
Sent by Gaia to kill Orion when he said he would kill all animals. It is also said that Apollo sent the
scorpion to kill Orion. Orion and Scorpio are on opposite sides of the sky.
Taurus - The Bull - Babylonian Origin
By the Romans, Jupiter turns into this bull to carry off Europa - daughter of King of Crete (and one
of the 7 sisters in the Pleaides). In Greek myth, it is said that Zeus brought the ram to try and win the
heart of Europa.
Virgo - The Virgin
Goddess of farms and harvest, Virgo is also known as Ishtar, Isis, Demeter, Cybele, and Athena. It is
also thought to represent Astraea, the daughter of Zeus representing justice or Persephone, queen of
the underworld.
Brief Side Topic: Zodiacal Lights
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While not having anything to do directly with the Zodiacal constellations,
Zodiacal Lights are often seen running perpendicular to the ecliptic.
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These lights are often described as a “false dusk” as it is a band of light that
appears to rise from the position of the setting or rising sun.
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The best times to see zodiacal lights are in the spring about an hour or two after
sunset, or in the fall about an hour or two before sunrise.
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This is a faint light so in order to see it you need to be in a fairly dark location.
From Fort Collins, going west into the mountains or east to the Pawnee National
Grasslands provides a dark enough sky to see these lights.
For more information
http://earthsky.org/astronomy-essentials/everything-you-need-to-know-zodiacal-light-or-false-dusk
Complete View of Zodiacal Light
Image Credit & Copyright: Miloslav Druckmüller (UM FSI, Brno Univ. of Technology), Shadia Habbal (IfA, Univ. of Hawaii)
How you are likely to view Zodiacal Light
Popular Constellation Stories
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Orion, Scorpio, Ophiuchus
Cassiopeia, Cephus, Andromeda, Cetus, Perseus,
Pegasus
The New Patterns in the Sky: Myths and Legends of the Stars, McDonald and Woodward Publishing
Company, 1996. ISBN: 0-939-92304-1
Homework
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On a clear night, look at stars all over the night sky
and observe the effects of Scintillation.
On a clear night, using a sky map (or other
resource) identify IAU constellations in the night
sky.
Extra Credit: On a clear night, go to a dark site
and observe the Zodiacal Lights about an hour or
two after sunset (western sky).