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Spring 2012 Astronomy Course
Mississippi Valley Night Sky Conservation
The Sky Around Us
Instructors:
Pat Browne
Stephen Collie
Rick Scholes
Course assistant
April 20 2012
Amy Booth
Announcements:
Errata – M46, M47 in the constellation Puppis
Course Assistant Amy Booth
Course Group online:
http://tech.groups.yahoo.com/group/
MoK_NSC/
invitations pending…
Program developed by
Mississippi Valley Conservation Authority
Royal Astronomical Society of Canada
Ottawa Astronomy Friends
Earth Centered Universe software for illustrations –
courtesy David Lane
II Stars in our Milky Way Galaxy
WHERE
Locating stars on the Celestial Sphere Constellations,
Aligning our telescopes to track the stars
WHEN
Do they rise and set on our local horizon
WHAT
Stellar properties, stellar designation,
classification
asterisms clusters of stars
WHO
Pioneers in stellar astronomy:
Annie Jump Canon
Helen Sawyer Hogg (Canadian)
Ejnar Hertzprung- Henry Russell
Last week on our plansiphere
Our first NightSky…
Objects on our Celestial Sphere =
Stars in our Milky Way Galaxy
Celestial Sphere – April 20 2012
Recall: What we see in the sky
depends
1.
2.
3.
4.
5.
Date
Time
What our latitude is which sets
our local horizon
Demo first on the planisphere
then on the celestial sphere
(local horizon)
Lets do this for April 20…
The stars rise 4 minutes earlier each
day
because the earth has also moved
through its orbit as it has rotated
around from night to day to night.
Star Time – Sidereal Time
A year on earth in star time…
Sidereal Time = our time measurement
with respect to the
stars..
1 Day = 1/365th of a circle
~ about one degree around the Sun.
Earth rotates on its axis as well as
rotates around the sun.
So, the time for a star to return to the
same place in our sky the following
evening is only 23 hours, 56 minutes and
4 seconds (not 24)
This is called a sidereal day ( 1
revolution of the earth with respect to the
stars)
Do the earth rotating dance around the
sun then with respect to the stars
infinitely far away…
Lets do
this for
Apr 20…
Say ‘goodbye” to winter
constellations
Observations from Last week
Open Clusters
Nebula and Stars
Globular Clusters
Galaxies
Mars
As the Earth Turns –Tour of the Night Sky
April 13 2012, 9pm EDT
N/S line - Meridian
M44
M67
When planning your are observing
session , start with the things that are
going to set first – Westward HO!
Here is the ECU view of the celestial
sphere showing the western sky,
You can see this on your planisphere.
But your planisphere does not record the
planets because they change from year to
year. ECU can program the planets in…
Jupiter, nearly set…
Venus (the brightest object)
We shall see a phase on Venus
Constellation Object
---------------- --------Taurus
M1 Crab Nebula – Supernova remnant
Taurus
M45 – the Pleaides – setting…
Gemini
M35 – Open Cluster
Auriga
M37,M36,M38 OCs
Orion
M42 Orion Nebula Emission, M78
M46,M47
M38
M1
M78
M42
We finish the Western tour with ruddy Mars
which is culminating on our meridian.
Venus
Venus
M45
line of the planets
(ecliptic)
Reflection Nebula
Monoceros M46, M47 OCs
Cancer
M44 Beehive Cluster , M67
M37
M36
M35
horizon (west)
Jupiter
What We Observed
Recall:
We went after the western Winter sky – objects that would soon
set.
These objects were mostly in the Winter Milky Way althouch you
couldn’t tell that because the sun was still lighting up the
horizon
We saw lots of Open Clusters . Their sizes/brightness
differences were obvious in Puppis (not Monoceros)
M47 vs M46
Cancer Beehive M44 vs M67
We saw Emission and Reflection Nebula like M42 and M43
which are in fact illuminating proto-stars
We saw a Supernova Remnant, the Crab Nebula in Taurus, …
the Cosmic Dust Bunny!
Particular observations?
Constellation
Celestial Object
Taurus
M1 Crab Nebula
Taurus
M45 Pleiades
Gemini
M35
Auriga
M37
Auriga
M36
Auriga
M38
Orion
M42
M43
M78
Puppis (not Monoceros)
M47
M46
Cancer
M44 Beehive
Cancer
M67
2700
6.1
30
M3 - Globular Cluster
33900
6.2
18
M51 - Whirlpool Galaxy
37000000
8.4
11x7
Ursa Major
M81
12000000
6.9
21x10
Ursa Major
M82 - peculiar galaxy
12000000
8.4
9x4
Leo
M65 - Leo Triplet
M66
Canes Venatici
Distance, Magnitude, Size
Constellation
Celestial Object
Distance (lys)
Magnitude
Size
Arc min
Taurus
M1 Crab Nebula
6300
8.4
6x4
Taurus
M45 Pleiades
440
1.6
110
Gemini
M35
2800
5.3
28
Auriga
M37
4400
6.2
24
M36
4100
6.3
12.0
M38
4200
7.4
21
M42
1300
4
85x60
M43
1300
9
20x15
M78
1600
8.3
8x6
M47
1600
5.2
30
M46
5400
6
27
Cancer
M44 Beehive
577
3.7
27
Cancer
M67
2700
6.1
30
M65 - Leo Triplet
60,000,000
9.3
8x1.5
M66
60,000,000
8.9
8x2.5
M3 - Globular Cluster
33,900
6.2
18
M51 - Whirlpool Galaxy
20,000000
8.4
11x7
Ursa Major
M81
10,000000
6.9
21x10
Ursa Major
M82 - peculiar galaxy
10,000,000
8.4
9x4
Orion
Puppis (not Monoceros)
Leo
Canes Venatici
Distance Graph and Brightness Graphs of what we saw
Galaxies
Globulars
Log
Distance dimming
When we look at Open Clusters, we are looking into the
disk of the Milky Way between 500 – 1000 light
years distance.
It turns out we are looking at two different spiral arms –
Auriga Open Clusters are in the Perseus Arm,
whereas the Orion/Puppis clusters are in the
Orion Arm
The brightest objects are the smaller magnitudes! !
Surface brightness depends on the concentration of
the
material as well as the distance to the object.
M1, the Crab nebula is considered a difficult object in
the city because of its low surface brightness.
When we look at Globular Clusters we are looking 10x
more deeply out of the disk of the galaxy in a haloIt is also on the higher end of the distance for these
around it – M3 is one example
asterisms.
Finally when we look at Galaxies, we are looking outside
of our own galaxy > 10,000,000 light years
Practical Procedures – when
thinking about Telescopes
What we practically need to know is
how
to set up our scopes if we have an
equatorial mount. …
Setting up our equatorial mount is
just like setting our local horizon on the
celestial sphere…
To set the scope polar axis to the celestial polar axis, the wedge is rotated to match the altitude of
polaris at your latitude.
This is the same thing as setting the altitude of the polestar equal to our latitude (45 deg)
Point the telescope North and
Look up the polar axis.
Se the altitude of the wedge to
•
your Latitude. To line us up
•
on the axis. We do this by
pointing to the Pole star
Polaris.
Polaris should be centered in the
eyepiece
www.astro-baby.com/simplepolar/simple_polar_alignment.htm
Celestial Coordinate System =
Equatorial Mount Coordinates
Once we are aligned, we only have to
nudge the Right Ascension axis
(around the polar axis), in order to
keep the object centered in the
eyepiece.
Because when we are aligned with our
polar axis we track the sky.
Polaris in not on the zenith
but roughly 45 degrees up
= our latitude above the
equator
Lines of Right
Ascension
Celestial Equator
The equatorial mount has the same axes as
the celestial sphere. It is an alt-azimuth
mount that has been tilted up to the pole star
so that one axis can be turned with the earth
turning.
Meridian facing north
Parallels of
Declination
Back to what’s out there in …
the Night Sky …
Star hopping to find objects does not require fancy mounts
Different scopes without equatorial mounts
When we observe…
1.
Always dress warmly as if it were still
winter.
2.
Standing around in the springtime can
get chilly because you are not moving
3.
Allow your eyes to adapt to what you are
seeing
4.
Learn not to stare into the eyepiece but
let your eye relax and allow the
peripheral vision to see things too
5.
Use a red flashlight to consult charts if
you are trying to hunt something down
6.
Keep an observing Log! and record
observations even if you’re tired
7.
“If you don’t keep a logbook you’ll
always be a beginner.”
Celestial Sphere
Earth Centered Universe
Computed for our location
Given our geographical position and
time on the earth: our latitude, our
time zone and our Time of Day, ECU
displays an accurate description of
our celestial sphere for our position
on the earth.
We can use a manual planisphere, set
it for our time of year and day for our
location to determine whether the
object is above our horizon, what our
L.S.T is, to place it on our meridian,
etc
We are ready to plan our observing
session and view not only stars, but
star clusters, galaxies,etc.
But everything, stars, asterisms,
constellations, galaxies have a time
and a season… according to sidereal
time.
M65, M65
Galaxies
Constellations: Area of sky identifiable
by star pattern
Ursa Major
Constellations and asterisms are not necessarily
close
to each other in space. Everything is at a nearly
‘infinite’ distance on our celestial sphere within our
Milky Way. This is to assign proper
oordinates to them.
Looking South then pan east or west
of our meridian
Click to see the major constellations
Bootes
Gemini
Historically, the brightest stars on were grouped
together into constellations and asterisms and the
brightest stars gained proper names.
Extensive catalogues of stars have been
assembled
by astronomers, which provide standardized star
designations.
Leo
Cancer
ecliptic
Greek Letters (Bayer Catalogue) order by relative
brightness so that Alpha Leonis is brighter than
Gamma.
Mars
Virgo
Their absolute positions in RA and DEC were
recorded at special Meridional telescopes fixed to
watch stars culminating on the meridian.
The ancients grouped those constellations
that traveled along the ecliptic
(the path of the planets) into the Zodiac
Saturn
Corvus
Hydra
There are 4 zodiacal constellations here…
Exercise 1:
Gemini, Cancer, Leo, Virgo
12 Zodiacal Constellations out of 88 modern Go out and observe these
ones (including Southern Hemisphere).
constellations. How many bright
stars can you see in them. Number
them…
Optional – DVD Chapters
4,5,6,7,8,9,11,12
When we observe stars naked eye …
Starlight and Spectra (some clues)
What visual clues tell us?
•
•
Brightness
Colour
Brightness doesn’t really tell us
the distance (parsecs or light
years) because we need to know
their intrinsic brightness
Colour – will tell us something
about their temperature
Other Properties
luminosity (intrinsic brightness)
and spectra (relative abundance
of spectral lines in the light from
the star),
Tell us about
-the age (> millions
of years)
- the distance to the object
-chemical composition
of the stellar object.
Without its spectral type a star is a meaningless dot.
Add a few letters and numbers like "G2V“ and the star
suddenly gains personality and character
WHAT is a star…
The Sun is a Star
Sun is below our horizon at 10 pm along the path of
the plane of the ecliptic
A star is a massive, luminous sphere
of plasma held together by gravity
At the end of its lifetime, a star can
also contain a proportion of
degenerate matter.
The nearest star to Earth is the Sun,
which is the source of most of
the energy on Earth.
In a plasma gas, a certain portion of
the particles are ionized. This is
because the gas is heated to high
temperatures at which point a gas
may ionize its molecules or atoms
(reduce or increase the number
of electrons in them), thus turning it
into a plasma, which contains charged
particles: positive ions and negative
electrons or ions.
This figure shows some of the more
complex phenomena of a plasma. The
colors are a result of relaxation of
electrons in excited states to lower energy
states after they have recombined with
ions. These processes emit light in
a spectrum characteristic of the gas being
excited.
Visual Star Colour and Star Spectra using
Spectroscope
When a star is brought into the field of view and the spectroscope is properly focused and adjusted, you
will see a beautiful spectrum with the colors of the rainbow spread out along its length. Depending on the
spectral type and luminosity class of the star, and your particular setup, you may see hydrogen lines
cutting perpendicular across the spectrum, or many fine lines of metals, or wide absorption bands of
molecules. These lines and bands in stellar spectra have been called the "fingerprints of the stars"
because their patterns identify the elements in a star's atmosphere and indicate a star's temperature.
These spectral features are easy to see in some classes of stars and more difficult to see in others.
The image below was taken with the Visual / Photo / CCD Star Spectroscope:
http://www.starspectroscope.com/index.html
How are spectral lines formed?
By electrons jumping between different energy levels in the atoms in
the
star's outer layers. Bound electrons can absorb and emit energy only
in certain discrete amounts.
When an electron absorbs a photon of light with just the right amount
of
energy, it jumps to a higher energy level. When the electron
spontaneously
jumps back to a lower energy level, a photon is emitted. Enough
electrons
jumping between any two given energy levels of a given element will
result in
a spectral emission or absorption line at a characteristic wavelength.
For example, the strongest spectral line in a hot main-sequence star
like Vega
lies in the blue-green part of the spectrum. It is a dark or
absorption line resulting from electron jumps from
the second to the fourth energy level of the neutral hydrogen atom,
Color Star Atlas or Color Stars in ECU
The main reason why stars are differently coloured is that some are hotter than
others.
Deep in their interior all stars are enormously hot (measured in millions of degrees),
but their temperature lessens towards their outer layers, and the coolest star
pours out most of their visible radiation in the red part of the spectrum.
Hotter stars like the Sun appear yellow, still hotter stars appear white, and the
hottest
appear blue.
The spectral type of a star is not the same thing as its intrinsic colour although
the two are closely related. When starlight passes through a spectograph ( a prism
or
glass grating) it is split into the colors of the rainbow, a spectrum. Most importantly
there are spectral absorption lines that give a clue to the temperature and the
chemical composition of that star Almost all starlight spectra can be
assigned to one of seven main types (OBAFGKM).
A great deal about the nature of the star can be inferred from its spectrum :
how bright it really is, how massive it is, whether it is a compact main sequence star
(see next slide) or a swollen giant. Broadly speaking, we can tell how old it is,
and what is happening to it with respect to its hydrogen, helium or
heavier element combustion process.
Coma Star Cloud – and star colours!
Hertsprung-Russell Diagram to classify Stars according to their Spectral Class
Stars and their Spectra
Most stars gather in certain narrow regions of the H-R diagram
according to their masses and ages. Stars arrive on what's called the
main sequencesoon after they are born, and this evolutionary track
is where they spend most of their lives.
Massive stars blaze brightly on the hot, blue end of
the main sequence. They burn up their nuclear
fuel in only millions or tens of millions of years.
Stars with lower masses comprise the yellow,
orange, and red dwarfs on the lower-right part of
the main sequence, where they remain for billions
of years.
As a star begins to exhaust the hydrogen fuel in its
core, it evolves away from the main sequence
toward the upper right and becomes a red giant or
supergiant. Stars that began with more than eight
times the Sun's mass then evolve left and right
through complicated loops on the H-R diagram as
if in a frenzy to keep up their energy production.
Then they finally explode assupernovae. Less massive
giants evolve to the left and then down to
becomewhite dwarfs; this is the track the Sun will
trace through the H-R diagram
Clas
s
Temperature[8
]
(kelvins)
Conventional
color
Apparent
color[9][10][11]
Mass[8]
(solar
masses)
Radius[8]
(solar
radii)
Luminosity
[8]
(bolometric
)
Hydroge
n
lines
Fraction of all
main sequence
stars[12]
O
≥ 33,000 K
blue
blue
≥ 16 M☉
≥ 6.6 R☉
≥ 30,000 L☉
Weak
~0.00003%
B
10,000–
33,000 K
blue to blue white
blue white
2.1–16 M☉
1.8–6.6R☉
25–
30,000 L☉
Medium
0.13%
A
7,500–
10,000 K
white
white to blue white
1.4–2.1M☉
1.4–1.8R☉
5–25 L☉
Strong
0.6%
F
6,000–7,500 K
yellowish white
white
1.04–1.4M☉
1.15–
1.4R☉
1.5–5 L☉
Medium
3%
G
5,200–6,000 K
yellow
yellowish white
0.8–1.04M☉
0.96–
1.15R☉
0.6–1.5 L☉
Weak
7.6%
K
3,700–5,200 K
orange
yellow orange
0.45–0.8M☉
0.7–
0.96R☉
0.08–0.6 L☉
Very
weak
12.1%
M
≤ 3,700 K
red
orange red
≤ 0.45 M☉
≤ 0.7 R☉
≤ 0.08 L☉
Very
weak
76.45%
Stellar classification is a classification of stars based on their spectral characteristics. The spectral classof a star is a designated
class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an
objective measure of the temperature in this chromosphere. Light from the star is analyzed by splitting it up by a diffraction grating,
subdividing the incoming photons into a spectrum exhibiting a rainbow of colors interspersed by absorption lines, each line indicating
a certain ion of a certain chemical element. The presence of a certain chemical element in such an absorption spectrum primarily
indicates that the temperature conditions are suitable for a certain excitation of this element. If the star temperature has been
determined by a majority of absorption lines, unusual absences or strengths of lines for a certain element may indicate an unusual
chemical composition of the chromosphere.
Most stars are currently classified using the letters O, B, A, F, G, K, and M (usually memorized by astrophysicists as "Oh, be a fine
girl, kiss me"), where O stars are the hottest and the letter sequence indicates successively cooler stars up to the coolest M class.
According to informal tradition, O stars are called "blue", B "blue-white", A stars "white", F stars "yellow-white", G stars
"yellow", K stars "orange", and M stars "red", even though the actual star colors perceived by an observer may deviate from these
colors depending on visual conditions and individual stars observed
http://en.wikipedia.org/wiki/Stellar_classification
Whether in a star's
atmosphere or in a
laboratory, absorption
lines are produced when a
continuous rainbow of light
from a hot, dense object
(top left) passes through a
cooler, more rarefied gas
(top center).
Stellar Spectra
tells us surface temperature,
chemical composition
atmospheric pressure and surface gravity,
total luminousity (energy pouring out)
http://www.skyandtelesc
ope.com/howto
/basics/330587
6.html?page=2
&c=y
Emission lines, by contrast,
come from an energized,
rarefied gas such as in a
neon light or a glowing
nebula.
When I look at a star, why do I see dark absorption lines rather than bright emission
lines?
Gas under high pressure produces a continuous spectrum, a rainbow of colors.
Continuous radiation viewed through a low density gas results in an absorption-line
spectrum.
What's happening here is that radiation emitted by gas under high pressure deep
within the star is being absorbed by low density gas in the star's outer layers.
We can show this in the lab:
Using a slit and prism, physicists discovered that when a solid, liquid, or dense gas is
heated to glow, it emits a smooth spectrum of light with no lines: a continuum. A rarefied hot
gas, on
the other hand, glows only in certain colors, or wavelengths: bright, narrow emission
lines instead of a rainbow band. If a cooler sample of the same gas is placed in front of a
glowing object emitting a continuum, dark absorption lines appear at the wavelengths
where the emission lines would be if the gas were hot.
What kinds of deep sky objects have emission-line spectra?
A low density gas shows an emission-line spectrum, when not observed against a
background of continuous radiation. Thus emission lines are found in the spectra of
planetary and diffuse nebulae, and in some stars. In the latter case the lines often
arise from gas clouds ejected from the star by strong stellar winds.
Annie Cannon 1863 –1941
Harvard College Observatory Astronomer
applied her own scheme which resulted in
the famous OBAFGKM classification which is still used today
The Sun's spectrum was marked by many narrow, black lines of various intensities.
These dark lines stayed at exactly the same places in the colorful band from day to
day
and year to year. This solar spectrum — a 'rainbow' of sunlight with thin,
dark absorption lines at numerous discrete wavelengths.
Each chemical element creates its own unique set of spectral lines.
Similar spectral lines showed up in laboratory
The sun is a G2 star representing 7.2% of the statistical
population within 10 pcs.
Class
Temperature[8]
(kelvins)
Conventional color
Apparent color[9][10][11]
Mass[8]
(solar masses)
Radius[8]
(solar radii)
Luminosity[8]
(bolometric)
Hydrogen
lines
Fraction of all
main sequence stars[12]
O
≥ 33,000 K
blue
blue
≥ 16 M☉
≥ 6.6 R☉
≥ 30,000 L☉
Weak
~0.00003%
B
10,000–33,000 K
blue to blue white
blue white
2.1–16 M☉
1.8–6.6R☉
25–30,000 L☉
Medium
0.13%
A
7,500–10,000 K
white
white to blue white
1.4–2.1M☉
1.4–1.8R☉
5–25 L☉
Strong
0.6%
F
6,000–7,500 K
yellowish white
white
1.04–1.4M☉
1.15–1.4R☉
1.5–5 L☉
Medium
3%
G
5,200–6,000 K
yellow
yellowish white
0.8–1.04M☉
0.96–1.15R☉
0.6–1.5 L☉
Weak
7.6%
K
3,700–5,200 K
orange
yellow orange
0.45–0.8M☉
0.7–0.96R☉
0.08–0.6 L☉
Very weak
12.1%
M
≤ 3,700 K
red
orange red
≤ 0.45 M☉
≤ 0.7 R☉
≤ 0.08 L☉
Very weak
76.45%
Stellar Spectra Summary
Stellar Spectra
1.
2.
3.
4.
surface temperature
chemical composition
atmospheric pressure and surface gravity
total luminousity (energy pouring out)
*The temperature sets the star's color and determines its surface brightness:
how much light comes from each square meter of its surface.
The atmospheric pressure depends on the star's surface gravity and therefore, roughly, on its size —
telling whether it is a giant, dwarf, or something in between.
The size and surface brightness in turn yield the star's luminosity (its total light output, or absolute magnitude
and often its evolutionary status (young, middle-aged, or nearing death).)
The luminosity (when compared to the star's apparent brightness in our sky)
also gives a good idea of the star's distance
T=5500
Note also that the colour of the star is related to the
corresponding peak wavelength emitted
T = 5000
of the continuous radiation:
λmax = b/ T
where λmax is the peak wavelength, T is the absolute
temperature
of the black body, and b is a constant of proportionality
called Wien's displacement constant, value).
http://en.wikipedia.org/wiki/Wien's_displacement_law
Knowing the suns temperature, we infer a particular
colour expressed as a wavelength in the visible …
λ = λ max
Stellar Classification - Who
•
http://astro.berkeley.edu/~gmarcy/women/cannon.html
Annie J. Cannon discovered that nearly all stars' spectra can be fit into one
smooth, continuous sequence. The sequence matched the stars' color
temperatures, from the hottest, blue-white stars at one end to relatively
cool, orange-red ones at the cool end . The basic sequence ran O B A F
G K M from hot to cool.
Planning your Observations
•
Get a book from the library or a magazine that
features a particular selection of objects visible
from your location at the current date
•
You can use ipod type devices but plan what
you are doing beforehand so that you don’t just
stare at the ipod
•
Better to plan indoors first . Use a planetarium
program like ECU. We can do a lab showing
how to set the time, place, information detail,
catalogues…
•
Make sure you are comfortable at the eyepiece
•
You can sit down when you get tired.
Plan your session.
Choose an area to work on and pick from a list
of different things:
stars with colour/ colour contrast
star clusters
star nebulae and nursuries
galaxies
supernovae remnants
clusters of galaxies
ECU
Earth Centered
Universe
Looking up – Spring Night Sky exploration
What binary stars can you see –
pick some famous ones
What color contrasts can you
observe?
Blue and yellow??
1. How do you use stellar
‘landmarks’ to hop to nonstellar objects such as the
Virgo Cluster of Galaxies
(hint – Find Epsilon Virgo and
Beta Leonis)
… or the cluster of galaxies in
2. Leo, M65,M66?
3What does the M stand for…
when we talk about Messier
objects?
4.What kinds of M
objects are there?
5.What kind of object is M44?
(The Beehive cluster)
Star- Hopping to find Star Clusters and Clusters of Galaxies
To find the Markarian Chain of
Galaxies in the Virgo cluster, locate
Epsilon Virginis and Beta Leo . They
lie
half-way along the line
To find M65, M65 drop
down from Theta Leonis
To find M3 (Globular Cluster) locate
Arcturus (Alpha Bootes) and Alpha
Canes Venatici (not shown) . M3 is 1/3
of the way from Alpha Bootes
See ObservingGalaxies.ppt on the
Millstone Website for more
information
Alpha Bootes