READING: Units: 59, 60

The Family of Stars

Stars come in all sizes…

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!

Massive stars burn brighter L~M 3.5

Luminosity Classes

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.

Evolution of low-mass stars

Evolution of high-mass stars

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

Our Sun will eventually A. Become white dwarf B. Explode as a supernova C. Become a protostar D. Become a black hole

The spectral type of a star is most directly related to its a.Absolute magnitude b. Surface temperature c. Size or radius d. Luminocity

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

Which is one of Kepler’s laws: a. For every action has an equal and opposite reaction b. Planets move in elliptical orbits c. F=ma d. Planets move in perfect circles around the sun

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

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

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

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

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

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

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

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

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

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

Light has properties a. of waves; b. of particles; c. none of the above; d. both a. and b.

What is the Law of Inertia? A body at rest stays at rest unless acted on by an outside force b. F=ma c. P^2=A^3 d. Fg=mMG/R^2

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