5.5 | Astrophysics and Cosmology

What are planets?

Objects with mass sufficient for their own gravity to force them to take a spherical shape, where no nuclear fusion occurs, and the object has cleared its orbit of other objects

What are dwarf planets?

Planets where the orbit has not been cleared of other objects

What are planetary satellites?

Bodies that orbit a planet

What are asteroids?

Objects which are too small and uneven in shape to be planets, with a near circular orbit around the sun

What are comets?

Small, irregularly sized balls of rock, dust, and ice that orbit the sun in eccentric elliptical orbits

What are solar systems?

The systems containing stars and orbiting objects like planets

What are galaxies?

Collections of stars, dust, and gas

What are nebulae?

Gigantic clouds of dust and gas that are the birthplace of all stars

What is needed for a star to form?

The temperature and pressure must be high enough for hydrogen gas nuclei in the protostar to overcome the electrostatic forces of repulsion and undergo nuclear fusion

What is meant by stable equilibrium?

The gravitational forces of the particles act to compress the star, but radiation pressure from photons emitted in fusion and gas pressure from nuclei in the core counteract this

Where do supergiants lie on the H-R diagram?

The top of the diagram - no matter the surface temperature, their massive size ensures high luminosity

Where do giants lie on the H-R diagram?

Midright of the diagram - big surface area allows them to emit big amount of total energy despite lower surface temperature

Where do main sequence stars lie on the H-R diagram?

Diagonal strip from top left to bottom right - depends on the mass of the star

Where do white dwarves lie on the H-R diagram?

Bottom left of diagram - very hot, but very small, resulting in a low luminosity