Comprehensive Astronomy: Constellations, Celestial Coordinates, Seasons, and Eclipses

Are constellations seasonal?

Yes, different constellations are visible in summer compared to winter, but some can be seen year-round.

How many constellations are there?

There are 88 constellations that cover the entire sky.

What defines a constellation in modern astronomy?

Constellations are defined as 88 non-overlapping sky regions that together cover the whole sky.

What is the relationship between stars and constellations?

Every star is located in a constellation.

Over what time scale do the patterns of stars in constellations change?

Thousands of years due to the motions of individual stars.

What fraction of the overall sky is north of the celestial equator?

Exactly one-half.

What is right ascension in celestial coordinates?

Right ascension is the coordinate equivalent to longitude, measured along the celestial equator.

What is declination in celestial coordinates?

Declination is the coordinate equivalent to latitude.

What governs the angle between an observer's horizon and the north celestial pole?

Latitude.

What is the celestial equator?

The celestial equator is the line in the sky that is perpendicular to Earth's spin axis.

What causes the nightly motion of objects across the sky?

The rotation of the Earth on its axis.

In which direction do stars appear to move due to Earth's rotation?

Eastward.

What basic pattern do stars near the north celestial pole appear to move in?

Circles, with the north celestial pole at the center.

What is the ecliptic?

The Sun's apparent path across the sky against the background stars.

How often does the Sun cross the celestial equator?

Twice a year, during the equinoxes.

What is the significance of the vernal equinox?

It is when the Sun crosses the celestial equator moving northward.

What occurs during the autumnal equinox?

The Sun crosses the celestial equator moving south.

When does the northern hemisphere experience summer?

When it is tilted toward the Sun, receiving more direct sunlight.

What is the tilt angle of the Earth's spin axis relative to the ecliptic?

23.5°.

What would happen to Earth's seasons if its axis of rotation were perpendicular to its orbital plane?

Earth would not experience seasons.

When is the shortest shadow of a vertical pole in the northern hemisphere?

At noon on June 21, the beginning of summer.

What is the 'Land of the Midnight Sun'?

A region where the Sun is above the horizon for 24 hours at certain times of the year.

What happens at the summer solstice in the northern hemisphere?

The Sun is at its highest angle in the sky for the whole year.

What fraction of the sky can an observer at the South Pole see?

50%.

How does the Sun appear to move in the sky at the South Pole on a midsummer day?

It appears to move parallel to the horizon at an elevation angle of about 23.5° for a full 24 hours.

How much time difference is there between clocks in New York and California during winter?

Clocks in New York are 3 hours ahead of those in California.

How does a solar day compare to a sidereal day on Earth?

A solar day is always longer than a sidereal day.

Why are leap years necessary?

Leap years are necessary because the length of a year is not an exact number of days.

Who introduced the leap year into our calendar?

Julius Caesar.

Who instituted the most recent correction to the calendar?

Pope Gregory XIII.

What is the true orbital period of the Earth around the Sun called?

One sidereal year.

What is the approximate length of the Earth's year?

Approximately 365¼ days.

What is precession in relation to the Earth's axis?

Precession is the very slow coning motion of the Earth's axis of rotation.

What causes the precession of the Earth's axis?

The gravitational pull of the Moon and the Sun on the equatorial bulge of the Earth.

Why do we see different phases of the Moon?

The illuminated half of the Moon becomes more or less visible from Earth as the Moon orbits the Earth.

What is the correct sequence of Moon phases in the sky?

Waxing crescent, first quarter, waxing gibbous, full Moon.

Where would you expect to see the true astronomical new Moon from the northern hemisphere?

The Moon is not visible at new Moon.

What phase is the Moon in when it is between the Sun and the Earth?

New Moon.

How much of the Moon's surface is illuminated at quarter phase?

About one half.

How often is the Moon visible in the daytime?

About half the time, or for two weeks in every month.

How must the Moon rotate to keep one face toward the Earth?

The Moon must rotate once per month, or once per orbit around the Earth.

What is the far side of the Moon?

The side of the Moon that is away from the Sun.

How long does it take for the dividing line between dark and light on the Moon to return to the same position?

29½ days.

What is the maximum number of eclipses that can occur in one year?

Seven or fewer.

What condition must be met for a lunar or solar eclipse to occur?

The Moon must be close to or crossing the ecliptic plane.

What causes a lunar eclipse?

The Moon passing into the shadow of the Earth.

During which type of lunar eclipse does the Moon remain longest in the Earth's shadow?

Total lunar eclipse.

What color does the Moon show during a total lunar eclipse and why?

A reddish color because only the red part of the solar spectrum is deflected onto it by the Earth's atmosphere.

What is the maximum length of totality for a lunar eclipse?

1 hour 47 minutes.

What is the difference between an umbral eclipse and a penumbral eclipse?

The distance of the Moon above or below the ecliptic.

Why is it more likely for a person to see a total lunar eclipse than a total solar eclipse?

A total lunar eclipse can be seen by people on most of the nighttime side of the Earth, while a total solar eclipse can only be seen in a narrow path.

What is the major factor that determines whether a solar eclipse is total or annular?

Earth-Moon distance.

What will a person standing in the Moon's penumbra see?

A partial solar eclipse.

What is the maximum time of totality for any total solar eclipse observed from the Earth's surface?

About 7.5 minutes.