Constellations

1. StarsStars

2. What is a Star?
• Hot glowing masses of Gases
• Composition: Mostly Hydrogen and
Helium

3. What is a star?What is a star?
• The objects that heat and light the
planets in a system
• A star is a ball of plasma held
together by its own gravity
–Nuclear reactions occur in stars (H 
He)
–Energy from the nuclear reactions is
released as electromagnetic radiation

4. What makes a Star Shine?
• The fusion of Atoms
Hydrogen atoms fusing to form Helium
releasing Heat, Light and energy
• Astronomers use a Spectroscope to determine
the composition of a Star

5. Classifying StarsClassifying Stars
• Color
• Temperature
• Size
• Composition
• Brightness

6. Star DistanceStar Distance
• Measured in Light-Years
• Light-Year: The distance light travels
in a year. (9.5 million million Kilometers)
5.87849981 × 1012
miles (6 trillion miles)
• Speed of light: 186,000 Miles/second
300,000 Kilometers/Second

7. Characteristics of StarsCharacteristics of Stars
• DISTANCE
–Measured in light-years
• The distance which a ray of light would
travel in one year
• About 6,000,000,000,000 (6 trillion) miles
• 186,000 miles per second

8. Finding the Distance to StarsFinding the Distance to Stars
• Parallax: The “apparent “ Shift that a star
has over a period of Time
• The closer the object, the more it will shift
position in the sky
*
Background Star

9. Determination of DistanceDetermination of Distance
Stellar Parallax
Knowledge of the distance to the
stars is crucial for our
determination of the luminosity
of stars…
• Current technology allows us to
determine the distance
accurately to within a few
hundred light-years.
• Hipparcos mission (European
Space Agency) measured the
stellar parallax of roughly
100,000 stars with precision of
a few milli-arcseconds. So, it
can measure distance of star up
to 1,000 light-years away…
Simulation of Stellar Parallax…

10. Astronomical Distance UnitsAstronomical Distance Units
• Light-year:
–The distance light travels (in vacuum) in
one year.
–one light-year is 10 trillion (1013
) km
• Parsec: parallax & arcsecond
–One parsec: the distance to an object
with a parallax angle of 1 arcsecond.
–One parsec equals to 3.26 light-year.
–kiloparsecs: 1,000 parsecs.
–megaparsecs: 1,000,000 parsec.

11. Characteristics of StarsCharacteristics of Stars
• Magnitude (brightness)
–A measure of brightness of celestial
objects
• Smaller values represent brighter objects
than larger values
–Apparent magnitude
• How bright a star appears to be from Earth
–Absolute magnitude (luminosity)
• How bright a star actually is

12. Star Brightness (magnitude)
• Absolute Magnitude: the “Real”
brightness of the star. How much light it
really gives off.(Need to know the distance
to the Star)
• Apparent Magnitude: How bright the star
appears to be.

13. Star Temperature
• Surface Temperature = Color
Blue-white White yellow orange red
Hottest *Sun coolest

14. Compare the sizes of StarsCompare the sizes of Stars
• Our Sun is a medium sized Star

15. Characteristics of StarsCharacteristics of Stars
• Temperature & Color
–The color of a star indicates the T of the
star
–Stars are classified by T
• Decreasing T (bright to dim)
• O, B, A, F, G, K, M [Oh Be A Fine Girl, Kiss
Me ]
http://www.seasky.org/cosmic/sky7a01.html

16. Hertzsprung-Russell DiagramHertzsprung-Russell Diagram
http://www.dustbunny.com/afk/stars/lifecycle/hrdiagram.gif

17. • Not all stars are the same
color because different
elements burn different
colors. Some are red, some
are blue, etc.
• Color tells the temperature
of the star
• Hot stars are bluish/white
and cooler stars are
reddish/orange
• Astronomers call this a
star’s spectral class.
Spectral classes are O, B,
A, F, G, K, and M
STARS ARE CLASSIFIED BY THEIR SIZE, COLOR
AND TEMPERATURE
Flame Test Clip

18. O, B, A, F, G, K, and M... (Oh Be A Fine Guy Kiss Me)
and for you guys: Oh Be A Fine Girl Kiss Me!!

19. Hertzsprung-Russell DiagramHertzsprung-Russell Diagram
(H-R Diagram)(H-R Diagram)
• Stars are ranked on
the H-R Diagram
based on their
temperature and
absolute magnitude
• Most stars fall in the
middle of the
diagram, called the
main sequence
• Very few stars are
white dwarfs or
giants/supergiants

20. H-R Diagram---shows theH-R Diagram---shows the
life cycle of starslife cycle of stars
temperature
Absolutemagnitude
M
ain sequence
supergiants
giants
White
dwarfs

21. Main Sequence StarsMain Sequence Stars
• A major grouping of stars that forms a
narrow band from the upper left to the
lower right when plotted according to
luminosity and surface temperature on the
Hertzsprung-Russell diagram

22. Types of StarsTypes of Stars
ClassificationClassification
Class Temperature Color
O 20,000- 60,000 K Blue
B 10,000 – 30,000 K Blue-white
A 7,500 – 10,000 K White
F 6,000 – 7,500 K Yellow-white
G 5,000 – 6,000 K Yellow
K 3,500 – 5,000 K Orange
M 2,000 – 3,500 K Red

23. Type
Hydrogen
Balmer
Line
Strength
Approximate
Surface
Temperature
Main Characteristics Examples
O Weak > 25,000 K
Singly ionized helium emission or absorption
lines. Strong ultraviolet continuum.
10 Lacertra
B Medium 11,000 - 25,000 Neutral helium absorption lines .
Rigel
Spica
A Strong 7,500 - 11,000
Hydrogen lines at maximum strength for A0
stars, decreasing thereafter.
Sirius
Vega
F Medium 6,000 - 7,500 Metallic lines become noticeable.
Canopus
Procyon
G Weak 5,000 - 6,000
Solar-type spectra. Absorption lines of
neutral metallic atoms and ions (e.g.
singly-ionized calcium) grow in strength.
Sun
Capella
K
Very
Weak
3,500 - 5,000
Metallic lines dominate. Weak blue
continuum.
Arcturus
Aldebaran
M
Very
Weak
< 3,500
Molecular bands of titanium oxide
noticeable.
Betelgeuse

24. -10
-5
0
5
10
15
-0.5 0 0.5 1 1.5 2 2.5
B-V Color Index
AbsoluteVisualMagnitude
White Dwarfs
Main Sequence
Giants
Bright Supergiants
Supergiants
Bright Giants
Subgiants
Stars of the same spectral class can be distinguished from one another by
using the luminosity effect to determine their size. It is found that, when we
consider the data for a large number of stars, the points on the Hertzsprung-
Russel diagram are approximately as shown below. There are very few stars
that don’t have MV and B – V that plot near one of the lines in the graph.
Based on this, we classify stars by luminosity as well as spectral class.
The luminosity
classes are
Ia bright
supergiant
Ib supergiant
II bright giant
III giant
IV subgiant
V main
sequence

25. http://www.answers.com/topic/stellar-classification

26. Life Cycle of StarsLife Cycle of Stars
http://hea-www.cfa.harvard.edu/CHAMP/EDUCATION/PUBLIC/ICONS/life_cycles.jpg

27. Life Cycle of StarsLife Cycle of Stars
• Begin their lives as clouds of dust and gas called
nebulae
• Gravity may cause the nebula to contract
• Matter in the gas cloud will begin to condense into
a dense region called a protostar
• The protostar continues to condense, it heats up.
Eventually, it reaches a critical mass and nuclear
fusion begins.
• Begins the main sequence phase of the star
• Most of its life is n this phase

28. Life Cycle of StarsLife Cycle of Stars
Life span of a star depends on its size.
– Very large, massive stars burn their fuel much
faster than smaller stars
– Their main sequence may last only a few
hundred thousand years
– Smaller stars will live on for billions of years
because they burn their fuel much more
slowly
• Eventually, the star's fuel will begin to run
out.

29. Life Cycle of StarsLife Cycle of Stars
• It will expand into what is known as
a red giant
• Massive stars will become red
supergiants
• This phase will last until the star
exhausts its remaining fuel
• At this point the star will collapse

30. Life Cycle of StarsLife Cycle of Stars
• Most average stars will blow away their
outer atmospheres to form a planetary
nebula
• Their cores will remain behind and burn as
a white dwarf until they cool down
• What will be left is a dark ball of matter
known as a black dwarf

31. Life Cycle of StarsLife Cycle of Stars
• If the star is massive enough, the collapse
will trigger a violent explosion known as a
supernova
• If the remaining mass of the star is about
1.4 times that of our Sun, the core is
unable to support itself and it will collapse
further to become a neutron star

32. Life Cycle of StarsLife Cycle of Stars
• The matter inside the star will be
compressed so tightly that its atoms are
compacted into a dense shell of neutrons.
• If the remaining mass of the star is more
than about three times that of the Sun, it
will collapse so completely that it will
literally disappear from the universe. What
is left behind is an intense region of gravity
called a black hole
• life-cycle-of-a-star-discuss 1b.ppt

33. Life Cycle of StarsLife Cycle of Stars
VideosThe Life Cycle of a Star - Animation.mp4VideosThe Life Cycle of a Star - Animation.mp4
http://www.seasky.org/cosmic/sky7a01.html

35. VideosVideos