Astro 150 Trivia - Review for Exam 2

Choose the correct order of the layers of the sun, from innermost to outermost

• Core, radiative zone, convective zone, corona

• Corona, convective zone, radiative zone, core

• Corona, radiative zone, convective zone, core

• Core, convective zone, radiative zone, corona

If protons repel each other, how come they stick together during nuclear fusion?

• The density of these particles is so high that they're forced together

• Protons and antiporotons are what's fusing together, not protons with other protons

• The particles are moving so fast that they can overcome EM repulsion

• We know it happens, we just don't know HOW it happens

Answer explanation

Stellar cores are environments of extreme heat and pressure. Protons are zooming around so fast that they are able to get close enough to each other for the strong nuclear force to kick in before electromagnetic repulsion tries to push them apart again.

A star has a parallax angle of 0.05 arcseconds. How far away is the star?

• 20 lightyears

• 20 parsecs

• 400 lightyears

• 400 parsecs

Answer explanation

The formula that lets you find distance from parallax angle is distance = 1/parallax angle. The parallax angle would be in arcseconds and the distance would be in parsecs.

Which of these is related to proper motion (see figure)?

• v_tan

• v_sp

• v_rad

According to the Doppler Effect, if a star's lines appear bluer, what does that tell us?

• The star is moving away from us

• The star has a high proper motion

• The star is passing behind dust clouds

• The star is moving toward us

Answer explanation

According to the Doppler Effect, objects moving toward you have blueshifted spectral lines, and objects moving away from you have redshifted spectral lines.

Why is brightness not the best quantity to use to determine the nature of a star?

• Brightness doesn't tell us WHY a star is bright

• It's too hard to determine without sensitive equipment

• Brightness CAN tell us a lot about a star

• It's too easily confused with luminosity

Answer explanation

According to the brightness equation, a star can either be bright because it's close, or because it's luminous. We need to determine at least one of those quantities if we really want to learn about a star. The brightness is easily found, and once we find the distance, we can find the luminosity, and vice versa.

What does the color of a star tell us?

• Its distance

• How fast the star is moving toward/away from us

• The luminosity of the star

• The star's temperature

What's the difference between a star and a brown dwarf?

• Not much; a brown dwarf is just the smallest type of star

• Stars can fuse regular hydrogen in their cores, brown dwarfs cannot

• Stars can fuse lithium in their cores, brown dwarfs cannot

• Stars can fuse deuterium in their cores, brown dwarfs cannot

Answer explanation

Brown dwarfs can only fuse the most easily fused materials in their cores. That is basically only lithium and deuterium (an isotope of hydrogen with one proton and one neutron in the nucleus, as opposed to regular hydrogen which is just one proton in the nucleus). And related, brown dwarfs are much less massive than even the smallest stars.

Where are the most massive stars placed on the HR diagram?

• The left side

• The right side

• The top left

• The bottom right

Answer explanation

The most massive stars are both blue and very luminous. Stars like that are found in the top left side of the HR diagram.

Consider three main sequence stars A, B, and C, each of which has a mass of 1.0M_sun, 3.0M_sun, and 5.0M_sun, respectively, where M_sun is the solar mass. Which one below is the correct order of increasing luminosity?

• C, B, A

• A=B=C

• A,B,C

• need distance to determine.

Answer explanation

The more massive a MS star is, the more luminous it is.