Harvard Spectral Classification
There are 7 spectral Classes (O,B,A,F,G,K,M). This order is based on decreasing surface temperature. A
Class stars have the strongest Hydrogen lines, while M Class stars have the weakest hydrogen lines.
Each class is then subdivided into 10 subdivisions (0-9).
The following is a table with properties of each of the spectral classes.
Spectral Class Properties
Type
Temperature (Kelvin)
Color
Hydrogen
O
30,000-60,000
Blue
Weak
B
10,000-30,000
Blue-White
Medium
A
7,500-10,000
White
Strong
F
6,000-7,500
White
Medium
G
5,000-6,000
Yellow
Weak
K
3,500-5,000
Yellow-Orange
Very Weak
M
2,000-3,500
Red
Very Weak
The following is the class of each of the stars on the list:
Class O- None on the list
Class B- Rigel, Spica, Regulus, Algol, and Spica
Class A- Vega, Sirius A, Deneb, Altair, and Castor
Class F- Procyon, and Polaris
Class G- The Sun, and Capella
Class K- Arcturus, Aldebaran, and Pollux,
Class M- Betelgeuse, Wolf 359, and Antares
Yerkes Spectral Classification
The Yerkes Spectral Classification is based on luminosity and temperature. It is also known as
luminosity classes. There are seven main luminosity classes:
Type Ia- Bright Supergiants
Type Ib- Normal Supergiants
Type II- Bright Giant
Type III- Normal Giant
Type IV- Sub-Giants
Type V- Main Sequence
Type VI- Sub-Dwarf
VII- White Dwarf
Galaxies
There are three main types of galaxies: Spiral, Elliptical, and Irregular.
Spiral Galaxies
An example of a spiral galaxy: (M31 Andromeda Galaxy)
Spiral Galaxies are named so because they have prominent spiral arms and a central "galactic nucleus"
or central bulge.
An example of a Barred-Spiral Galaxy: (NGC 1300)
Spiral Galaxies also have a very large rate of star formation in the spiral arms of the galaxy. Also,
almost all spiral galaxies have a galactic halo that surrounds the galaxy. These halos contain stray stars
and globular clusters. It is also theorized that many spiral galaxies have supermassive black holes at the
center of the galaxy. Our own galaxy, The Milky Way, is a spiral galaxy, and is also theorized to have a
supermassive black hole at its center, called Sgr A*. There is also a sub-division of spiral galaxies,
known as barred-spiral galaxies. Barred-spirals have a central bar, and then have spiral arms shooting
off at each end of the bar.
The spiral galaxies on the list for 2009 are:
- M31 Andromeda Galaxy (in Andromeda)
- M51 Whirlpool Galaxy (In Canes Venatica)
- Milky Way Galaxy (Barred-Spiral)
Elliptical Galaxy
Elliptical Galaxies appear just like they sound- they are elliptical/ spherical. Elliptical Galaxies contain
mostly old Population II stars, and also, they have a very low rate of star formation because there is
barely any interstellar matter in elliptical galaxies. There is the least amount of elliptical Galaxies in
the known Universe.
An example of an Elliptical Galaxy:(M84)
The Elliptical Galaxies on the list for 2009 are:
-M84 (in Virgo)
Concerning M84, some astronomers believe that it actually may be a Lenticular Galaxy (which is a halfway point between a Spiral galaxy and an Elliptical galaxy)
Irregular Galaxies
Irregular also appear just how they sound- they are without a definite shape. They are normally formed
by Spiral or
An example of an Irregular Galaxy
Elliptical Galaxies that have been deformed by different forces- such as gravity. They contain a lot of
interstellar matter.
The Irregular Galaxies on the list for 2009 are:
-Large Magellanic Cloud (in Dorado and Mensa)
-Small Magellanic Cloud (in Tucana)
The Sun
Star Identification
The best way to study for the first part of the event is to go outside and look at the sky. If you are not
familiar with the constellations this is a great way to learn them. Look up into the sky and use a star
chart to find a few constellations and stars. Doing this even a few times a month really pays off.
Another great way to study for this event to get you ready to go outside is to make flash cards with the
constellation on the front and the name and the deep sky objects on the back.
It is helpful if you can relate easy-to-find constellations such as Orion or Ursa Major (Big Dipper) to the
constellations around them. This guides you to the constellation via others, rather than having to rely
only on the shape. On your reference sheet, you may want to include a section about how to find the
constellations you have trouble with.
Stellar Information
"Students will demonstrate an understanding of the basic concepts of mathematics and astrophysics
relating to stellar evolution."
For the second part of the event you have to know about the general characteristics of stars, galaxies,
star clusters, etc. You must be able to figure out a star's spectral class, surface temperature, and
evolutionary stage (i.e. giant, supergiant, main sequence, white dwarf) by reading an H-R diagram.
Another thing you should do is learn the life cycles of various types of stars. Look at some of the
pictures below and try to put them in order.
You should also be familiar with redshift and blueshift and how they are related to the (theoretical)
creation of the universe, something that many people overlook.
Another aspect of the event that is new for 2009 is that you must be able to label a model of the sun
and be familiar with its spectral class and placement on an H-R diagram as well as other general
characteristics.
You are asked to use information which includes the following:
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Hertzsprung-Russell diagrams
Spectra
Light curves
Kepler's laws
Energy transfer
Impulse-momentum
Circular motion
Radiation laws (Wien's and Stefan-Boltzmann)
Period-luminosity relationship
Stellar magnitudes and classification
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Parallax
Slides
Photographs
Star charts and animations
You may also be asked to complete activities which include:
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Determine answers relating to stellar birth
Determine answers relating to stellar evolution and the Hertzsprung-Russell diagram
Determine answers relating to the motions and evolution of star systems
Identify and be knowledgeable about multi-wavelength images of the different stages of
stellar evolution listed above
Identify, know the location, be knowledgeable about, and/or answer questions relating to
the stellar evolution of the
following objects...
Pictures
Know these pictures!!!: (Harvard's Chandrasekhar X-Ray Observatory and Hubble Space Telescope are
to be credited with these images)
Cas A (Cassiopeia A) - super nova remnant (infrared, optical, radio, and X-ray images)
M1 (Crab Nebula) - Nebula (infrared, optical, radio, and X-ray images
Crab Pulsar - fastest pulsar known (30 pulses per second)
Orion Trapezium Cluster - 4 hot young stars in an open cluster in the Orion Nebula
Familiarize yourself with these pictures, print them out, or put them on your laptop.
Variable Stars
A variable star is defined as a star that undergoes changes in luminosity. In Science Olympiad, you will
be tested on your knowledge of various DSOs (Deep Sky Objects), types of variable stars, and other
related things.
Variable stars are generally placed into two categories; Intrinsic variable stars and Extrinsic variable
stars.
Intrinsic Variable Stars
Intrinsic Variable Stars are stars that change in luminosity due to physical changes in the star; there are
three types of Intrinsic Variable Stars.
The first type is pulsating variable stars. These are stars that periodically swell and shrink. Pulsating
variable stars that have short periods are called Cepheids; cepheids usually have more regular periods
than Longer Period Variables. Important examples include the Delta Cepheid variables, W Virginis
variables, RR Lyrae variables, and Beta Cephei variables.
The other type of pulsating variable are long period variables. They have longer periods than cepheids
(such as a year or longer) and have a much less regular period. These variables are also sometimes
bigger and cooler than cepheids. A good example is the Mira Variables. Long period Variables can be
split into three subgroups. The First is Irregular variables; these are usually red super giants and have
almost no regular period. Second is the Semi regular variables, these sometimes go through regular
periods, then change and go on an un-regular period. And third are Nonradial pulsators; variables that
change to shapes other than the sphere to change magnitude.
The second major type of intrinsic variable star are eruptive variable stars. These are stars are mostly
pre-main sequence stars, but an exceptional few main sequence stars are eruptive variables. Pre-main
sequence (also called protostars) are stars that have not completed the process of becoming a mainsequence star from a gas nebula and are not yet condensed. So while condensing they change in
magnitude. Eruptive Main-sequence variables are usually extremely larger or extremely smaller than
the average main sequence star. Some eruptive variables are red giants since they easily lose their
gases. The last type of eruptive variable star is binary eruptive stars. These stars flare up and can
remain that way for 1-4 years. Important eruptive variable stars are the Orion Variables, the WolfRayet variables, and RS Canum Venaticorum variables.
The third major type of an intrinsic variable star is a cataclysmic or explosive variable star. The most
dramatic type of these variable stars are called Supernovae. This only occurs in extremely massive and
old stars. The outer layers of the star are expelled at high speeds creating a supernovae remnant or
nebula. A white dwarf or pulsar is usually left behind. The second type of these variables are called
Novae. They are dramatic explosions caused by a pair of close binaries but don’t cause the total
destruction of the star. An other type are dwarf novae and are very similar to novae. Dwarf novae are
just two binary white dwarfs that regularly have outburst. The fourth and final type of intrinsic
variable are Z Andromedae Variables. These are a less common type of variable and are caused by a
double star system containinga red giant and a hot blue star; enclosed in a cloud of dust and gas.
Extrinsic Variable Stars
Extrinsic variable stars can stars that change in luminosity due to external changes; the two major
types are rotating and eclipsing.
Rotating variable stars are stars that change in luminosity due to the rotation of the star. This can
happen because of such things as a sunspot on the surface as it rotates. This can also occur when two
close binary stars change shape due to their mutual gravity. Fluctuations in magnetic fields can cause
slight change in magnitude.
The second type of extrinsic variable star are eclipsing variable stars. These are caused when stars in
double star systems eclipse, causing a lowing of magnitude. However, this variation can only be viewed
from certain angles. Planetary transits can also cause a very small variation in luminosity only viewed
with very accurate instruments.
Other Topics
In competition, this is the major topic tested. But you will have to have to interpret data and identify
deep sky objects (such as M13; seen below). The test may ask you to read a light curve, know the
composition of stars, or give examples of variables.
This Year's DSO's (Deep Sky Objects)
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Milky Way Galaxy (MWG)
Sagittarius A
Andromeda Galaxy (M31)
The Cartwheel Galaxy
M84
M33
NGC 604
M33 X-7
C153
M82
SN1994D
Sn1993J
M15
G1
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Epsilon Aurigae
-*is part of a special viewing campaign this year and will be included up to at least 2011.
Helpful Tips
Identification certainly is not the most important part of this event but I have found it is it easiest way
to begin your study. For the rest of the event, you must study the things mentioned in the table above
(make it a checklist if you want). This task is facilitated by Astronomy Today--I have found all the
information I have ever needed, either during a test or after a test, in that book.
Sometimes, the test will use a StarLab or planetarium for the identification portion. I would advise
putting some time in to familiarize yourself with how the skies look on it.
Also, there is always a chance that a bad star map may be used, so make sure to get yourself
accustomed to anything that may be thrown at you.
The best way to study for the identification part, is not only maps, but actually going outside and
finding constellations and stars in the night sky. Not only is star-gazing fun, but it is one of the best
ways to learn the location of the constellations and the stars that are on the list.
SAMPLE TEST
65 points total
Part I: Star ID section (25 pts):
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(1pt) Orion
(1pt) Canis Major
(1pt) Gemini
(1pt) Cepheus
(1pt) Taurus
(1pt) Leo
(1pt) Saturn
(1pt) Jupiter
(1pt) Betelgeuse
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(1pt) Aldebaran
(1pt) Rigel
(1pt) Pollux
(1pt) Pleiades
(2pts) M42, the Great Nebula in Orion
(2pts) M31, Andromeda Galaxy
(2pts) M1, the Crab Nebula
(3pts) M16, the Eagle Nebula
(3pts) Image: SN1987A
Part II: Knowledge Tasks (35 pts):
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(1pt) What component of the solar system is located between the orbits of Mars and
Jupiter?
The asteroid belt.
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(2pts) Why is there no atmosphere on the Moon or Mercury?
There is not enough gravity to hold the gases in place during the hottest part of the day.
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(2pts) What causes the Moon's phases?
The Sun illuminates a different 50% of the Moon than the 50% that Earth sees. The part that
overlaps is the part that we see illuminated from Earth at any particular phase.
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(2pts) What is the most reliable method for measuring distances to nearby stars?
Parallax. By using triangulation and observing the nearby stars from different positions along
Earth's orbit we can calculate the distance to the object with simple geometry.
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(2pts) On the H-R diagram there is a slightly wavy line of stars that runs diagonally down
from left to right. Most stars are on that line. What is the name of that line of stars?
The Main Sequence.
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(2pts) On the H-R diagram Stars in the upper right corner are both bright and "cool."
How can a cool star be brighter than a hot star?
The star is bigger. Stars in the upper right corner of the H-R diagram are "Giants" thus, even
though each square meter of surface my radiate less light, there is a LOT more surface area.
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(2pts) At the end of the Sun's life, what type of star will it become and where will it be
located on the H-R diagram.
White dwarf. These are located in the bottom left corner of the H-R diagram.
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(2pts) Stars that are just entering "old age" start to pulsate. These stars reside in a region
on the H-R diagram called the "instability strip." What makes these stars unstable?
They are "changing fuel." I.e., They are changing from hydrogen fusion to helium fusion.
Because of the different temperatures and volumes involved the star is unstable until it adjusts to
the new fuel.
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(2pts) Why isn't there a lunar eclipse every month at the time of full moon?
The plane of the Moon's orbit is tilted by 5 from the plane of Earth's orbit. Since the Moon is
only 0.5 wide, most of the time it is either too high or too low to be in Earth's shadow.
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(2pts) Two stars are the same age and mass. Star "A" is four times as bright as star "B."
Which star is further away and by how much?
Star "B" is further away by a factor of 2. Because of the 1/r2 drop off of light intensity, doubling
the distance decreases the brightness by a factor of 4.
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(2pts) How many times brighter or dimmer is a 1st Magnitude star as compared to a 2nd
Magnitude star? Which star is brighter?
2.5 times. The 1st Magnitude star is brighter.
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(2pts) How do we use "light" to measure the temperature of a star? The Sun's temperature
is 5800 K what would be the actual value of "whatever it is" that is measured by an
astronomer?
By using blackbody radiation. We measure the continuous spectrum of the star and determine
which color (wavelength) is brightest. From That we can determine the temperature of the star.
By Wien's law: (max. wavelength in nm) = 2.9×106 / (T in Kelvin) wavelength = 500 nm.
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(2pts) What data make us think that many spiral galaxies contain super-massive black
holes in their cores?
Strong radio and x-ray emissions, jets of matter ejected, and/or enormous orbital velocities (as
measured by the Doppler red shift and blue shift) of the stars near the core as measured by
Kepler's and Newton's laws.
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(3pts) What causes the seasons and why is winter cold and summer hot?
Earth's axis is tilted relative to the plane of the orbit. Thus in winter the sunlight strikes Earth at
an oblique angle which spreads out the light over more surface area - the light is less intense.
Also, the tilt of the axis causes the days to be shorter in winter. Hence we have both weaker light
and less time in that light to warm the surface. In summer the reverse is true.
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(3pts) What is "sidereal time" and, how can one use the right ascension of stars to
immediately determine the current sidereal time?
Sidereal time is time measured relative to the stars rather than the Sun. (A sidereal day is about 4
minutes shorter than a mean solar day.) The current local sidereal time is exactly equal to the
right ascension of any star that happens to be on the meridian (line from north to south through
the overhead point, or zenith) at that moment.
(The last three problems have been removed from this web site because I plan to use them
again.)