READING:

1
READING
Units 59, 60
2
The Family of Stars
3
Stars come in all sizes
4
The Mass-Luminosity Relation

• If we look for trends in stellar masses, we
  notice something interesting
• Low mass main sequence stars tend to be cooler
  and dimmer
• High mass main sequence stars tend to be hotter
  and brighter
• The Mass-Luminosity Relation
• Massive stars burn brighter!

5
Massive stars burn brighter
LM3.5
6
Luminosity Classes
7
Stellar Evolution Models and Observation

• Stars change very little over a human lifespan,
  so it is impossible to follow a single star from
  birth to death.
• We observe stars at various stages of evolution,
  and can piece together a description of the
  evolution of stars in general
• Computer models provide a fast-forward look at
  the evolution of stars.
• Stars begin as clouds of gas and dust, which
  collapse to form a stellar disk. This disk
  eventually becomes a star.
• The star eventually runs out of nuclear fuel and
  dies. The manner of its death depends on its
  mass.

8
Evolution of low-mass stars
9
Evolution of high-mass stars
10
Tracking changes with the HR Diagram

• As a star evolves, its temperature and luminosity
  change.
• We can follow a stars evolution on the HR
  diagram.
• Lower mass stars move on to the main sequence,
  stay for a while, and eventually move through
  giant stages before becoming white dwarfs
• Higher mass stars move rapidly off the main
  sequence and into the giant stages, eventually
  exploding in a supernova

11
Our Sun will eventually
A. Become white dwarf
B. Explode as a supernova
C. Become a protostar
D. Become a black hole
12
The spectral type of a star is most directly
related to its

• Absolute magnitude
• b. Surface temperature
• c. Size or radius
• d. Luminocity

13
Which two vital parameters are used to describe
the systematics of a group of stars in the HR
diagram?

• a. Mass and weight
• b. Luminocity and radius
• c. Surface temperature and mass
• d. Luminocity and surface temperature

14
Which is one of Keplers laws

• a. For every action has an equal and opposite
  reaction
• b. Planets move in elliptical orbits
• c. Fma
• d. Planets move in perfect circles around the sun

15
A solar exlipse can occur ONLY when

• a. the Moon comes between the Earth and the Sun
• b. the Sun comes between the Moon and the Earth
• c. the Earth comes between the Moon and the Sun
• d. the Sun, Moon and Earth form a precise
  right-angled triangle

16
When dropped by an astronaut on the Moon, two
objects of different mass will

• a. Have different accelerations proportional to
  their masses
• b. Have different accelerations, the more massive
  object having the smaller acceleration
• c. Have the same acceleration
• d. Have no acceleration at all in the airless
  space

17
According to Newton's laws, a force must be
acting whenever

• a. an object's position changes
• b. the direction of an object's motion changes
• c. time passes
• d. an object moves with non-zero speed

18
Kepler's first law states that a planet moves
around the Sun

• a. in a circle with the Sun at the center
• b. in an elliptical orbit, with the Sun at the
  center of the ellipse
• c. in an elliptical orbit, with the Earth at the
  center of the ellipse
• d. in an elliptical orbit, with the Sun at one
  focus

19
If an object has an orbit around the Sun that has
an essentricity of 0.1, then the orbit is

• a. a straight line
• b. exactly circular
• c. almost circular, but not quite
• d. a long, thin ellipse

20
What causes sunspots?

• a. differential rotation on the Sun creates
  vortices, or eddies, which are cooler and darker
  than the rest of the solar surface
• b. solar flares cause the photoshere to expand
  and cool in the vicinity of the flare
• c. magnetic fields breaking through the
  photosphere inhibit heat conduction where the
  field is strong
• d. masses of heavy elements occlude solar light

21
Spectral types (e.g. O, B, A, F, G, K, M) define
uniquely their

• a. surface temperatures
• b. luminosities
• c. sizes of radii
• d. brightnesses

22
Which of the following astronomical systems are
held together by gravity

• a. The Sun
• b. The Solar System
• c. The Milky Way
• d. All of them

23
If a new planet were found with a period of
revolution of 6 years, what would be its average
distance from the Sun?

• a. About 1AU
• b. About 3.3 AU
• c. About 6 AU
• d. About 36 AU

24
In order of increasing wavelength the
electro-magnetic spectrum is

• a. gamma rays, blue light, red light, radio
  waves
• b. ultraviolet, gamma rays, blue light, radio
  waves
• c. red light, radio waves, X rays, blue light
• d. visible, ultraviolet, X-rays, radio

25
Light has properties

• a. of waves
• b. of particles
• c. none of the above
• d. both a. and b.

26
What is the Law of Inertia?

• A body at rest stays at rest unless acted on by
  an outside force
• b. Fma
• c. P2A3
• d. FgmMG/R2

27
What is retrograde motion?

• a. backward moving/ or interrupted movement of
  a planet on the sky
• b. Clockwise rotation of the moon around the
  earth
• c. Rotation of planets around the sun
• d. Large elliptical movements of comets