Chapter 2
How many arcseconds are in a full circle?
1.296×106 arcseconds
How many arcminutes are in a full circle?
2.16×104 arcminutes
If Earth's rotation slowed down so that it completed exactly one rotation about its axis in 100 hours, what would be the typical time interval between sunrise and sunset?
50 hours
What do astronomers mean by a constellation?
A constellation is a region in the sky as seen from Earth.
When we see Saturn going through a period of apparent retrograde motion, it means
Earth is passing Saturn in its orbit, with both planets on the same side of the Sun.
What is the celestial sphere?
The celestial sphere is a representation of how the entire sky looks as seen from Earth.
We see two stars separated by one degree on the celestial sphere. What can we infer about these stars?
They rise and set at about the same time
About how many stars are visible to the naked eye on a clear, dark night away from city lights?
about two thousand
As Earth goes around the Sun each year, Earth's rotation axis in the North points
in the direction of the celestial pole, near Polaris, throughout the year.
If the Sun rises precisely due east
it must be the day of either the spring or fall equinox
The North Celestial Pole is 35∘ above your northern horizon. This tells you that you are at:
latitude 35∘ N.
Two stars that are in the same constellation:
may actually be very far away from each other.
If there is going to be a total lunar eclipse tonight, then you know that
the Moon's phase is full
The fact that we always see the same face of the Moon tells us that
the Moon's rotation period is the same as its orbital period
In winter, Earth's axis points toward the star Polaris. In spring
the axis also points toward Polaris.
What is the ecliptic?
the path the Sun appears to trace around the celestial sphere each year
A week after full moon, the Moon's phase is
third quarter
Beijing and Philadelphia have about the same latitude but very different longitudes. Therefore, tonight's night sky in these two places:
will look about the same
When it is summer in Australia, the season in the United States is
winter