Homework 3

What is the phase of the Moon if it is highest in the sky at sunrise?

third quarter

The intersection of the Earth's orbital plane and the lunar orbital plane is called the line of nodes.

true

Which of the following lunar phases is not possible to see at 6 PM?

waning gibbous

You look at the Moon and notice that more than half of the side facing the Earth is illuminated, and that it is illuminated on the left-hand side. Because of this, you know that it is a

waning gibbous moon

At approximately what time does the Moon rise when it is a new moon?

sunrise

The Moon is highest in the sky when it crosses the meridian, halfway between the time of moonrise and the time of moonset. What is the phase of the Moon if it is highest in the sky at midnight?

At midnight the local zenith points into space on the side of Earth away from the Sun. The meridian passes from pole to pole through the zenith, so the Moon, when it crosses this line, is also on the side of Earth away from the Sun: full moon.

Explain the difference between sunlight and moonlight.

Both originate at the Sun, but sunlight comes directly to us while moonlight is reflected off the Moon on its way to us.

Could the Moon ever appear at your zenith if you are at the south pole?

The celestial equator is along the horizon, 90° from your zenith, if you are at the south pole. Since the Moon has a declination of ±28½°, it will never be anywhere near your zenith.

The name of one of the lunar phases in the Dakota language means "diminishing moon." To which phase would this term most likely apply?

Waning Crescent

You are meeting a friend for a late dinner at 9 PM. While waiting for him, you notice the Moon near the western horizon. What phase is it?

Waxing Crescent

On a particular day, the moon rises in the waxing gibbous phase. What phase is it when it sets?

Waxing Gibbous

What is the phase of the Moon if it is highest in the sky at noon?

new

At approximately what time does the Moon rise when it is a full moon?

sunset

At approximately what time does the Moon rise when it is a first quarter moon?

noon

Find the approximate age of a waning gibbous moon.

18½ days

On average, lunar eclipses occur about how often?

2 times a year

Find the approximate age of a third quarter moon.

22 days

At what time does a waning crescent moon set?

3 PM

Astronomers sometimes refer to lunar phases in terms of the age of the Moon. This is the time that has elapsed since new moon phase. Thus, the age of a full moon is half of a 29½-day synodic period, or approximately 15 days. Find the approximate age of a waxing crescent moon.

3½ days

Why is the line of nodes important to the subject of eclipses?

An eclipse can take place only when an extension of the line of nodes passes through the Sun.

A common misconception about the Moon's phases is that they are caused by the Earth's shadow. Explain why this not correct.

Earth's shadow only reaches the Moon when it is on the opposite side of the Sun from Earth-when it is full. Thus the shadow cannot account for the phases.

How did Eratosthenes measure the size of the Earth?

Eratosthenes determined the size of Earth by measuring the difference in the direction of the Sun's rays relative to the local vertical at two locations a known distance apart

A Waxing Crescent Moon occurs when the Earth casts a circular shadow over most of the Moon.

False

A partial eclipse can be seen by fewer people at one time than a full eclipse can.

False

We see the Moon because it shines by its own light.

False

If the Moon is in the first quarter phase today, what phase will it be one week from now?

Full Moon

One definition of a "blue moon" is the second full moon within the same calendar month. There is usually only one full moon within a calendar month, which is why the phrase "once in a blue moon" means "hardly ever." Why are blue moons so rare?

Full moons are separated by one synodic month, about 29 1 2 days. Since the longest months are 31 days long, a blue moon can occur only if the full moon happens to fall on the first day or early on the second day of the month, which does not happen very often. (For a 30-day month, the full moon would have to fall early on the first day.)

Explain why the Moon exhibits phases.

Half the Moon is illuminated by the Sun at all times. But, because of the changing positions of Earth, Moon, and Sun, the half of the Moon facing Earth can be entirely illuminated, not illuminated at all, or illuminated to any amount between these two extremes. These are the phases.

Why doesn't a lunar eclipse occur at every full moon and a solar eclipse at every new moon?

In order for an eclipse to occur the Sun, Earth, and Moon must be nearly along a straight line. Because the Moon's orbit is tilted slightly with respect to the ecliptic, this does not occur for every full or new moon.

The total lunar eclipse of October 28, 2004, was visible from South America. The duration of totality was 1 hour, 21 minutes. Was this total eclipse also visible from Australia, on the opposite side of the Earth?

No, lunar eclipses are visible only from the night side of Earth. The length of totality is insufficient to allow Australia to rotate to the night side during the eclipse.

Can one ever observe an annular eclipse of the Moon?

No. An annular eclipse of the Sun can occur when the Moon is too far away or the Sun is too close so that the Moon doesn't quite cover the Sun, leaving a ring of the Sun visible at the height of the solar eclipse. Earth's shadow, on the other hand, is always much larger than the full moon, so there can be no annular lunar eclipse.

During an eclipse, the shadow of the Earth appears curved as it moves across the Moon because of the following.

The Earth is round.

Why does the Moon appear red during a total eclipse?

The Earth's atmosphere scatters red light onto the moon during a total eclipse, giving it a reddish appearance.

You are watching a lunar eclipse from some place on the Earth's night side. Will you see the Moon enter the Earth's shadow from the east or from the west?

The Moon moves eastward, so it enters the Earth's shadow from the west.

The plane of the Moon's orbit is inclined at a 5° angle from the ecliptic, and the ecliptic is inclined at a 23½° angle from the celestial equator. Could the Moon ever appear at your zenith if you lived at the equator?

The celestial equator is your zenith if you are at the equator. The Moon's orbit will be above the ecliptic at some times of the year and below at other times. Since the ecliptic can be above or below the zenith, the Moon will always have a declination (±28½°) that can place it at the zenith viewed from the equator.

What is the line of nodes?

The line of nodes is the line that connects the two points in the Moon's orbit where the orbit crosses the ecliptic.

A Full Moon occurs when the half of the Moon facing Earth is also the half of the Moon illuminated by the Sun.

True

Are there any months of the year in which it would be impossible to have two full moons?

Yes, February

At what phase in its monthly cycle will the Moon be seen high in the sky in the late afternoon from mid-latitudes?

first quarter

What is the phase of the Moon if it is highest in the sky at sunset?

first quarter

At approximately what time does the Moon rise when it is a third quarter moon?

midnight