Stars Astronomy Midterm

Neutrinos

are related to electrons but have no charge and very little (but NOT zero) mass

• fusion in the sun

• barley interacts with anything of the universe , only affected by the weak force and gravity

Equation to find distance

parallax

• or inverse square law if yk luminosity

Equation to find luminosity

Inverse square law

Temperature

color of spectrum (Wien’s law)

Radius

L-R-T

What is the brightest star in the sky

Sirius

what is the biggest star

Antares

How do we measure mass

through gravity

• Newton’s Law

Force

a push or pull

Acceleration

the change in motion caused by force

Ellipses & Focus points

the locations where the sum of the distances from two “focus” points is the same

The center of mass (Binary stars)

the location where you could balance the system

• Closer to more massive object, further from less massive

• EX: a seesaw

Newton & Kepler’s Third Law

P² ∝ a³/M total

• P = total time to complete an orbit

• a = semi-major axis (separation on the sky + distance)

• m total = the combined mass of the two orbiting objects

• Depends on the total mass of the things orbiting

Total Mass (m total)

Most stars orbit each other in paris (BINARY SYSTEMS)

• Measuring their orbital motions allows us to determine M total

The HR-Diagram

plots stellar luminosity against surface temperature

• X axis is surface temperature (red right, blue left)

• Y axis is luminosity

• OBAFGKM (hottest to coolest)

lower temperature and higher luminosity = bigger stars

The main sequence

Most stars lie along a single Main Sequence

• 90% of stars lie on here, 9% are red giants, 1% are white dwarfs

What is on the lower left of the HR diagram

White dwarfs

• small, HOT, not luminous

What is on the upper right of the HR diagram

Giant branch

• same temp as but larger than main sequence

• red giants

ONLY on the main sequence

The very hottest stars are also the bluest, brightest, and the largest

• Bigger in radius, higher in luminosity

• smallest stars are low in luminosity and red

All determined by mass!

The luminosity of main-sequence

determined by mass

• L ∝M^4

• Radius goes up with mass too

Equation for stellar lifetime mass

stellar lifetime ∝ 1/(stellar mass)³

• or Lifetime(of a star) ∝ mass^-3

Interstellar Medium (ISM)

The stuff between the stars

• Provides the raw material for star formation

  • GAS & DUST

Gas

atoms and small molecules, mostly hydrogen and helium

Dust

Large molecules that have too many atoms where you can’t name it

Interstellar Gas

• The dominant component, the rest is stars

• very diffuse, very low density

• all almost entirely empty