ASTRO ch 18

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

1/20th of an arcsecond

A light curve for a star measures how its brightness changes with

Time

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:

at the same distance

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

If an astronomer wants to find the distance to a star that is not variable and is located too far away for parallax measurements, she can:

find the star's luminosity class from its spectrum and read the luminosity from an H-R diagram

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

A type of star that has turned out to be extremely useful for measuring distances is

the Cepheid variables

The higher the luminosity (intrinsic brightness) a Cepheid variable is,

the longer the period of its variations

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

½ the diameter of the Earth's orbit around the Sun