Chapter 18-19

If a star is 20 parsecs away, its parallax must be:

1/20th of an arcsecond

If a star is 10 parsecs away, how long ago did the light we see from it tonight begins its journey toward us?

32.6 years

How far away would a star with a parallax of 0.2 arcsec be from us?

5 parsecs

In an H-R diagram, where can you see the spectral type of a star (whether it is an O type star or a G type star, for example)?

Along the bottom (the horizontal axis)

One of your good friends who is on a diet asks you to point out the stars with the smallest mass on an H-R diagram that you are studying. Where are you sure to find the stars with the lowest mass on any H-R diagram?

Among the stars at the bottom right of the main sequence

Why did it take astronomers until 1838 to measure the parallax of the stars?

Because the stars are so far away that their annual shift of position in the sky is too small to see without a good telescope

Today, astronomers can measure distances directly to worlds like Venus, Mars, the Moon, or the satellites of Jupiter by:

Bouncing radar beams off them

Astronomers identify the main sequence on the H-R diagram with what activity in the course of a star's life?

Fusing hydrogen into helium in their cores

Who was the astronomer who is the "H" in H-R diagram?

Hertzsprung

Measurements show a certain star has a very high luminosity (100,000 times the Sun's) while its temperature is quite cool (3500 K). How can this be?

It must be quite large in size

Stars that lie in different places on the main sequence of the H-R diagram differ from each other mainly by having different:

Masses

A team of astronomers discovers one of the most massive stars ever found. If this star is just settling down in that stage of its life where it will be peacefully converting hydrogen to helium in its core, where will we find it on the H-R diagram?

Near the very top of the main sequence, in the upper left

As astronomers use the term, the parallax of a star is:

One half the angle that a star shifts when seen from opposite sides of the Earth's orbit

The original definition of a meter was:

One ten-millionth of the distance from the Earth's equator to its pole

Where on the H-R Diagram would we find stars that look red when seen through a telescope?

Only on the right side of the diagram and never on the left

A white dwarf, compared to a main sequence star with the same mass, would always be:

Smaller in diameter

An H-R Diagram plots the luminosity of stars against their:

Surface temperature

An astronomical unit is:

The average distance between the Earth and the Sun

What is the baseline that astronomers use to measure the parallax (the distance) of the nearest stars?

The diameter of the Earth's orbit around the Sun

The apparent brightness of stars in general tells us nothing about their distances; we cannot assume that the dimmer stars are farther away. In order for the apparent brightness of a star to be a good indicator of its distance, all the stars would have to be:

The same luminosity