4.7 Eclipses of the sun and moon  (Page 7/32)

When Earth’s Northern Hemisphere is tilted toward the Sun during June, some would argue that the cause of our seasons is that the Northern Hemisphere is physically closer to the Sun than the Southern Hemisphere, and this is the primary reason the Northern Hemisphere is warmer. What argument or line of evidence could contradict this idea?

Where are you on Earth if you experience each of the following? (Refer to the discussion in Observing the Sky: The Birth of Astronomy as well as this chapter.)

1. The stars rise and set perpendicular to the horizon.
2. The stars circle the sky parallel to the horizon.
3. The celestial equator passes through the zenith.
4. In the course of a year, all stars are visible.
5. The Sun rises on March 21 and does not set until September 21 (ideally).

In countries at far northern latitudes, the winter months tend to be so cloudy that astronomical observations are nearly impossible. Why can’t good observations of the stars be made at those places during the summer months?

What is the phase of the Moon if it . . .

1. rises at 3:00 p.m.?
2. is highest in the sky at sunrise?
3. sets at 10:00 a.m.?

A car accident occurs around midnight on the night of a full moon. The driver at fault claims he was blinded momentarily by the Moon rising on the eastern horizon. Should the police believe him?

The secret recipe to the ever-popular veggie burgers in the college cafeteria is hidden in a drawer in the director’s office. Two students decide to break in to get their hands on it, but they want to do it a few hours before dawn on a night when there is no Moon, so they are less likely to be caught. What phases of the Moon would suit their plans?

Your great-great-grandfather, who often exaggerated events in his own life, once told your relatives about a terrific adventure he had on February 29, 1900. Why would this story make you suspicious?

One year in the future, when money is no object, you enjoy your birthday so much that you want to have another one right away. You get into your supersonic jet. Where should you and the people celebrating with you travel? From what direction should you approach? Explain.

Suppose you lived in the crater Copernicus on the side of the Moon facing Earth.

1. How often would the Sun rise?
2. How often would Earth set?
3. During what fraction of the time would you be able to see the stars?

In a lunar eclipse, does the Moon enter the shadow of Earth from the east or west side? Explain.

Describe what an observer at the crater Copernicus would see while the Moon is eclipsed on Earth. What would the same observer see during what would be a total solar eclipse as viewed from Earth?

The day on Mars is 1.026 Earth-days long. The martian year lasts 686.98 Earth-days. The two moons of Mars take 0.32 Earth-day (for Phobos) and 1.26 Earth-days (for Deimos) to circle the planet. You are given the task of coming up with a martian calendar for a new Mars colony. Would a solar or lunar calendar be better for tracking the seasons?

What is the right ascension and declination of the vernal equinox?

What is the right ascension and declination of the autumnal equinox?

What is the right ascension and declination of the Sun at noon on the summer solstice in the Northern Hemisphere?

During summer in the Northern Hemisphere, the North Pole is illuminated by the Sun 24 hours per day. During this time, the temperature often does not rise above the freezing point of water. Explain why.

On the day of the vernal equinox, the day length for all places on Earth is actually slightly longer than 12 hours. Explain why.

Regions north of the Arctic Circle are known as the “land of the midnight Sun.” Explain what this means from an astronomical perspective.

In a part of Earth’s orbit where Earth is moving faster than usual around the Sun, would the length of the sidereal day change? If so, how? Explain.

In a part of Earth’s orbit where Earth is moving faster than usual around the Sun, would the length of the solar day change? If so, how? Explain.

If Sirius rises at 8:00 p.m. tonight, at what time will it rise tomorrow night, to the nearest minute? Explain.

What are three lines of evidence you could use to indicate that the phases of the Moon are not caused by the shadow of Earth falling on the Moon?

If the Moon rises at a given location at 6:00 p.m. today, about what time will it rise tomorrow night?

Explain why some solar eclipses are total and some are annular.

Why do lunar eclipses typically last much longer than solar eclipses?

Suppose Earth took exactly 300.0 days to go around the Sun, and everything else (the day, the month) was the same. What kind of calendar would we have? How would this affect the seasons?

Consider a calendar based entirely on the day and the month (the Moon’s period from full phase to full phase). How many days are there in a month? Can you figure out a scheme analogous to leap year to make this calendar work?

If a star rises at 8:30 p.m. tonight, approximately what time will it rise two months from now?

What is the altitude of the Sun at noon on December 22, as seen from a place on the Tropic of Cancer?

Show that the Gregorian calendar will be in error by 1 day in about 3300 years.