Astronomy Ch. 2

What do astronomers mean by a constellation?

A constellation is a region in the sky as seen from Earth. The stars in a constellation all lie in approximately the same direction from Earth but may be at different distances.

Which of the following correctly describes the meridian in your local sky?

A half-circle extending from your horizon due north, through your zenith, to your horizon due south This path does not have a common name.

Each choice describes how a few astronomical phenomena are related to time periods. Which list is entirely correct? (Careful: some lists are partially correct.)

Earth's rotation defines a day. The cycle of the Moon's phases takes about a month. Earth's orbit defines a year. Earth's cycle of axis precession takes 26,000 years. These statements are all true.

If we have a new moon today, when we will have the next full moon?

In about two weeks The complete cycle of phases from one new moon to the next new moon takes about a month, so about a month after new moon we would have another new moon.

What is stellar parallax?

It is the slight back-and-forth shifting of star positions that occurs as we view the stars from different positions in Earth's orbit of the Sun. Stellar parallax does not have anything to do with real stellar motion.

During the time that a planet is in its period of apparent retrograde motion: _________

Over many days or weeks, the planet moves westward relative to the stars, rather than the usual eastward relative to the stars All celestial objects must rise in the east and set in the west because the daily pattern of rise and set is caused by Earth's west-to-east rotation.

If you are located in the Northern Hemisphere, which of the following correctly describes a relationship between the sky and your location?

The altitude of the north celestial pole equals your latitude. This sentence is almost complete nonsense because it uses every technical term incorrectly.

Which of the following statements does not use the term angular size or angular distance correctly?

The angular distance between those two bright stars in the sky is about 2 meters. This sentence uses the term correctly, but we are looking for one that uses it incorrectly.

What is the celestial sphere?

The celestial sphere is a representation of how the entire sky looks as seen from Earth. Note that the celestial sphere is not meant to represent physical reality but rather the appearance of the sky from our planet.

What do we mean when we talk about the Milky Way in our sky?

The patchy band of light that outlines the plane of the Milky Way Galaxy as seen from Earth. We live in what we call the Milky Way Galaxy, but the Milky Way that we see in our sky is only a small part of our entire galaxy.

What is the ecliptic?

The path the Sun appears to trace around the celestial sphere each year This half-circle describes the meridian in the local sky.

What is the saros cycle?

The roughly 18-year cycle over which the pattern of eclipses repeats The saros cycle is related to the Moon, not the Sun and seasons.

Which of the following best describes why we have seasons on Earth?

The tilt of Earth's axis causes different portions of the Earth to receive more or less direct sunlight at different times of year. Recall the scale of the solar system discussed in Chapter 1 of The Cosmic Perspective. Earth is so small compared to the distance to the Sun that any difference in distance between the two hemispheres is completely unimportant.

About how many stars are visible to the naked eye on a clear, dark night away from city lights?

a couple thousand Of these, we use the brightest ones to identify the outlines of the constellations.

We cannot see a new moon in our sky because _________.

a new moon is quite near the Sun in the sky Half the Moon, the half facing the Sun, is always illuminated by sunlight (except during a lunar eclipse).

Stars that are visible in the local sky on any clear night of the year, at any time of the night, are called _________.

circumpolar All objects in the heavens are said to be celestial.

Lunar eclipses can occur only during a _________.

full moon Eclipses cannot occur at quarter phases.

We describe a location on Earth's surface by stating its _________.

latitude and longitude Latitude describes location north or south of the equator, and longitude describes location east or west of the prime meridian. Together, latitude and longitude pinpoint a location on Earth's surface.

The Moon always shows nearly the same face to Earth because ________.

the Moon rotates once in the same amount of time that it takes the Moon to orbit Earth once This is what we call synchronous rotation, and as shown in Section 2.3 of The Cosmic Perspective, it explains why the Moon keeps nearly the same face to Earth at all times.

The point directly over your head is called _________.

the zenith Note that the zenith is therefore defined only for the local sky.