Astronomy: Chapter 2

A calendar year, from vernal equinox to vernal equinox, is called a

tropical year.

A star rises at 8 P.M., moves across the sky (crossing high overhead), and then sets at

8 A.M.

A star with RA = 4^h is in your meridian at a certain time. Which of the following stars will be on your meridian 2.5 hours from now?

RA = 6^h 30^m

At a certain time the star straight overhead has a Right Ascension of 2 hours and 30 minutes. One hour later this same star will have a Right Ascension of

2 hours and thirty minutes.

At what approximate value of declination was the Sun on June 21 this year?

23.5°

At what approximate value of right ascension was the Sun this year on March 21?

0 hours

At what approximate value of right ascension was the Sun this year on September 22?

12 hours

At what average speed does the Sun appear to move across our sky with respect to the stars in order to move through one full circle in one year?

about 1° per day

Describing a star as being in the constellation Cygnus (the Swan) tells a modern astronomer that the star is

somewhere in a particular region of sky having definite boundaries.

Diurnal motion of objects in the sky is caused by the

rotation of Earth on its axis.

During a given night, some stars will be observed to pass through the

zenith

Earth would not have seasons if

its axis of rotation were perpendicular to its orbital plane.

For an observer at a fixed location on Earth, the angle between the north celestial pole and an observer's horizon depends on the

observer's latitude (north or south of the equator).

If the polar axis of Earth precesses through a full circle (See Figure 2-20 of Universe, 10th ed.) in 26,000 years, how long will it take for the line between the axis and the center of the circle to move through 1°?

72 years

If the unaided human eye is sensitive enough to see about 6000 of the stars in the entire sky, about how many stars would be seen at one time on a given night from a single location from which the horizon is completely visible around the observer?

3000

If you were standing on the equator, which one of the following positions in the sky would pass through your zenith at some time in one 24-hour period?

the position of the vernal equinox, or 0 hours right ascension, 0° declination

In modern astronomy, the constellations are

88 regions of sky, covering the entire sky.

It is warmer in summer than winter because

the Sun is higher in the sky and the days are longer.

Precession is

a very slow conical motion of Earth's axis of rotation.

Precession of Earth's axis of rotation is caused by

the gravitational pull of the Moon and the Sun on the equatorial bulge of Earth.

The celestial coordinates that together describe a star's position precisely and unambiguously are

right ascension and declination.

The ecliptic crosses the celestial equator at

two points, known as equinoxes.

The summer solstice position coordinates are RA = 6^h 0^m 0^s, declination = +23° 27´. What are the coordinates of the winter solstice?

RA = 18^h 0^m 0^s, declination = –23° 27´

The “Land of the Midnight Sun” is so named because

the Sun is above the horizon for a full 24 hours at a certain time of the year.

What is the declination of Polaris (The North Star)?

90°

What is the declination of the Sun?

a number which changes significantly over a day

What is the right ascension of the Sun?

a number which changes significantly over a day

Where must you stand on Earth to have the celestial equator pass through your zenith?

the equator

Which of the following statements correctly describes the relationship between stars and constellations?

Every star is located in a constellation.

You are observing from the east coast of the United States as a star rises above the horizon. At this same instant your friend on the west coast will find that this star

has not yet risen.