Astronomy Chapter 2

What are circumpolar stars? Are more stars circumpolar at the North Pole or in the United States? Explain.

A circumpolar star is a star that always remains above the horizon for a particular latitude.

What are constellations? How did they get their names?

A constellation is a region of the sky with well defined borders. All 88 constellations received their names and borders in 1928 by the International Astronomical Union.

What do we mean by apparent retrograde motion of the planets? Why was this motion difficult for ancient astronomers to explain? How do we explain it today?

Apparent retrograde motion is the apparent motion of a planet during the period of a few weeks to a few months when it appears to move west relative to the stars in the sky. It was difficult for ancient astronomers to explain this because they were reluctant to let go of the idea that earth was the center of the universe. Today, scientists are explaining it as the earth passing the object in its revolution or rotation

Suppose Earth's axis had no tilt. Would we still have seasons? Why or why not?

If the earth had no tilt, we would have no seasons. The orientation of the axis is relative to the sun changes; the northern hemisphere is tilted towards the sun in June and away in December.

What are latitude and longitude? Does the sky vary with latitude? Does the sky vary with longitude? Explain.

Latitude measures the north/south position on Earth, where longitude measures the east/west position. Latitude affects the sky because it affects the horizon and the zenith. Longitude, however, does not vary.

What is precession, and how does it effect what we see in our sky?

Precession is the gradual wobble that alters the orientation of the earths' axis in space. This affects what we see in our sky over the course of 26,000 years. Today, Polaris is considered our North star. In time, Vega will be the north star as the axis will point towards it.

What is stellar parallax? How did an inability to detect it support an ancient belief in Earth-centered universe?

Stellar parallax is the apparent shift in position of a nearby star that occurs as we view the star from different positions in earths' orbit of the sun each year. Because ancient Greeks could not detect the angular separation of stars, without aid, they determined earth was the center of the universe

Explain why we can measure only angular sizes and angular distances for objects in the sky. What are arcminutes and arcseconds?

The angular size of an object is the angle it appears to span in your field of vision. The angular distance between a pair of objects is the angle that appears to separate them. We use angular size and angular distance to describe an objects place in the sky because our lack of depth perception on the celestial sphere, hampering our ability to judge the true sizes or separation of objects. Arcminutes and arcseconds are more precise forms of astronomical measurement. Each degree is separated into arcminutes and further subdivided into arcseconds

Why does the local sky look like a dome? Define horizon, zenith, and meridian. How do we describe the location of an object in the local sky?

The horizon is the boundary between the Earth and sky. The zenith is the point directly overhead; the meridian is an imaginary half circle stretching from the horizon due south to the horizon due north, passing through the zenith. We can pinpoint any object in the local sky by stating its direction along the horizon and its altitude above the horizon.

Briefly describe the moons cycle of phases. Can you ever see a full moon at noon? Explain.

The phases from a new moon to the full moon are called "Waxing" meaning increasing. The phases from the full moon to a new moon are called "Waning" meaning to decrease. You can't see a full moon at noon because it rises at 6pm and sets at 6am

Briefly describe key facts about the solstices and the equinoxes.

The summer solstice in June is when the northern hemisphere is most directly tipped towards the sun and receives most direct sunlight. The winter solstice in December is when the northern hemisphere receives the least direct sunlight. The spring equinox in March is when the northern hemisphere goes from being tipped slightly away from the sun to slightly towards it. The fall equinox in September is when the northern hemisphere is starting to tip away from the sun

What is the zodiac, and why do we see different parts of it at different times of year?

The zodiac are the constellations that make up the ecliptic. It is the sun's apparent location along the ecliptic that determines which constellations we see at night

Why do we always see the same face of the moon?

We always see the same face of the moon because of synchronous rotation, where the earth and the moon rotate on the axis in the same amount of time.

Why don't we see an eclipse at every new moon and full moon? Describe the conditions needed for a solar or lunar eclipse.

We don't see an eclipse at each new moon or full moon because eclipses only occur when the moon is in perfect alignment with the earth and sun while passing through the nodes. For a lunar eclipse, the earth has to lie directly between the sun and the moon, casting it's shadow on the moon. For a solar eclipse, the moon has to lie directly between the sun and the earth so as to cast it's shadow on the earth.

Suppose you were making a model of the celestial sphere with a ball. Briefly describe all the things you would need to mark on your celestial sphere.

When making a celestial sphere, one would need to mark the celestial north pole, which is directly over Earth's north pole. You'd also need to mark the celestial south pole, directly over Earth's south pole; and the celestial equator which is a projection of Earth's equator into space. Finally the ecliptic, which is the path the sun follows as it appears to circle around the celestial sphere once each year.

On a clear, dark night, the sky may appear to be "full" of stars. Does this appearance accurately reflect the way stars are distributed in space? Explain.

Yes, because when we look in any direction into the galactic plane, we see stars and interstellar clouds that make up the milky way in the night sky.