Quarks to Cosmos Lecture Sheet 9

Stars & the Sun

What are the stellar spectral classes and what does the order mean?

O, B, A, F, G, K, M. Ordered by decreasing temperature. Originally alphabetical by spectral line strength.

What is the Sun’s spectral class?

G2V.

Where are red giants, main sequence, and white dwarfs on the HR diagram?

Red giants = upper right; Main sequence = diagonal; White dwarfs = lower left.

What determines if a star is on the main sequence?

Hydrogen fusion in the core.

How does luminosity depend on mass?

L ∝ M^3–4.

How does lifetime depend on mass?

Lifetime ∝ 1 / M^2.5.

What are the regions of the Sun?

Core, Radiative zone, Convective zone, Photosphere, Chromosphere, Corona.

What is hydrostatic equilibrium?

Gravity inward balanced by pressure outward.

What powers the Sun?

Proton-proton chain: H → He + energy. E = mc².

Other products of the pp-chain?

Neutrinos.

How many solar neutrinos reach Earth?~10^38 per second.

Mass lost by Sun per second?~4 × 10^9 kg/s.

Age of the Sun?~4.6 billion years.