1. Which of the following describes a solar eclipse?
a. the earth is between the sun and the moon, and the earth is in the
moon's shadow
b. the earth is between the sun and the moon, and the moon is in the
earth's shadow
c. the moon is between the earth and the sun, and the moon is in the
earth's shadow
d. the moon is between the earth and the sun, and the earth is in the
moon's shadow
Choices a and c can be eliminated because, in them, shadows are pointing
toward the sun. Shadows cast by the sun must always point away from
the sun. b describes a lunar eclipse, and d describes a solar eclipse.
2. What is a light year?
a. a unit of time equal to 6 trillion seconds
b. the average distance between the Earth and the Sun
c. the distance light travels in a year
d. the time the Earth takes to orbit the Sun
If you remember nothing else from this class, I want you to remember that
a light year is a unit of distance, not time (Many movies
and TV shows get this wrong). A light year is the distance light travels
in a year, or about 9.5 trillion kilometers (6 trillion miles).
3. What is a parsec?
a. a unit of time equal to about 3.26 million seconds
b. a unit of angle equal to 1/3600 of a degree
c. the distance light travels in a year
d. the distance at which the parallax angle is 1 arcsecond
A parsec is another unit of distance that we used a lot in this class.
It's convenient if you are using trigonometric parallax to measure
distances (see question 4).
4. That famous observing team of Drs. Harden, Petrie, and Rozyczka measures
the parallaxes of the stars Sirius and Altair. They find that Sirius has
a parallax angle of 0.30 arcsecond, and Altair has a parallax angle of 0.15
arcsecond. What do they conclude?
a. Sirius is twice as far away as Altair
b. Altair is twice as far away as Sirius
c. Sirius is twice as large as Altair
d. Altair is twice as large as Sirius
Trigonometric parallax (or just "parallax") is the primary method used to
find distances to nearby stars. It works less and less well the farther
away the stars get (see question 5).