The Moon, Eclipses, and Tides

How does the Moon move across the sky?

• east to west

How much of the lunar surface is illuminated by the Sun at all times?

• half

How long does the Moon take to comple one “lunar cycle”?

29.5 days - about 1 month

The lunar cycle occurs from _______ to _________.

New Moon to New Moon

In respect to the Earth’s orbital plane, how many degrees is the Moon’s orbit tilted?

5 degrees

How many sides of the Moon are visible from Earth?

only one side

What is a blue moon?

• second full moon in a month

• does not occur in February

What is a harvest moon?

• the nearest full moon to the autumnal equinox

How much of the Moon’s surface has been seen from Earth?

• only 1/2

How long does it take the Moon to revolve around the Earth once?

• 27.3 days

How long does it take the Moon to rotate on its axis?

• 27.3 days

What type of orbit does the Moon have?

• synchronous orbit

Why can we only see the near side of the Moon?

• the Moon has a synchronous orbit

How long is a Sidereal Month and what is it?

• 27.3 days

• when the Moon completes it 360 degree revolution around the Earth

Synodic/Lunar Month

• 29.5 days

• completes the Lunar Cycle

How many additional days and degrees of lunar orbit to complete the Synodic Month?

• 2.2 days due to Earth’s revolution

• 29.04 degrees of lunar orbit

How many degrees per one day of lunar orbit?

• 13.19 degrees per day

Where is Earth in the Moon’s orbit?

F1

the point in the Moon’s orbit where it is closest to Earth

• Perigee

the point in the Moon’s orbit where it is the farthest from Earth

• Apogee

How far away is the Moon from the Earth at Perigee?

• 356,410 km

How far away is the Moon from the Earth at Apogee?

• 406,700 km

orbital velocity and the gravitational pull increase at…

Perigee

orbital velocity and the gravitational pull decrease at…

Apogee

apparent angular diameter increases as viewed from Earth at…

Perigee

apparent angular diameter decreases as viewed from Earth at…

Apogee

What is Earthshine?

• sunlight reflected off the Earth’s surface back onto the Moon **not direct light

Earthshine only occurs during the…

crescent phases

What mainly causes the Moon’s phases?

• revolution of the Moon around Earth

What also causes the Moon’s phases?

• Earth’s changing view of the illuminated ½ of the Moon

_____ of the Moon is always illuminated by the Sun but Earth can only see _____ of that half.

½ , parts

What is the exception to the rule that one half of the Moon is always illuminated by the Sun but Earth can only see parts of that half?

Lunar Eclipse

Waxing Phase

• after the New Moon

• illuminated portion is increasing

• light is on the right!!!

Waning Phase

• before the New Moon, after Full Moon

• the illuminated portion is decreasing

• light is to the left!!!

New Moon

• 0%

• Moonrise - 6 am

• Moonset - 6 pm

• Transit (highest alt) - 12 pm

• possible SOLAR eclipse

Waxing Crescent

• 25%

• Moonrise - 9 am

• Moonset - 9 pm

• Transit (highest alt) - 3 pm

1st Quarter

• 50%

• Moonrise - 12 pm

• Moonset - 12 am

• Transit (highest alt) - 6 pm

Waxing Gibbous

• 75%

• Moonrise - 3 pm

• Moonset - 3 am

• Transit (highest alt) - 9 pm

Full Moon

• 100%

• Moonrise - 6 pm

• Moonset - 6 am

• Transit - 12 am

• possible LUNAR eclipse

Waning Gibbous

• 75%

• Moonrise - 9 pm

• Moonset - 9 am

• Transit - 3 am

3rd Quarter

• 50%

• Moonrise - 12 am

• Moonset - 12 pm

• Transit - 6 am

Waning Crescent

• 25%

• Moonrise - 3 am

• Moonset - 3 pm

• Transit - 9 am

When do eclipses happen?

• when one celestial object blocks (node) another

• Moon, Sun, Earth

Two types of eclipses:

• lunar eclipse (common)

• solar eclipse (rare)

Eclipses can only occur during which phases?

New and Full Moons

2 types of shadows:

• Umbra

• Penumbra

Umbral Shadow

• darkest + innermost part of the shadow

Penumbral Shadow

• lighter and outside part of the shadow

What occurs during a total lunar eclipse?

• Moon orbits through Earth’s umbral shadow

• normally Moon would appear full

A lunar eclipse occurs during a _________.

Full Moon

3 types of Lunar Eclipses:

1. Penumbral

2. Total

3. Partial

What do the different types of Lunar Eclipses depend on?

• the exact alignment of the Sun, Earth, and Moon

Penumbral Eclipse

• Moon passes through the Penumbra only

Total Eclipse

• Moon totally incased in the Umbra

• RED

Partial Eclipse

• Moon passes through both Umbra + Penumbra

The Moon’s color depends on…

Earth’s atmospheric refraction + clarity

Lunar Eclipses occur how many times a year and for how long?

• twice a year

• for about an hour or two

Lunar Eclipses can be seen by…

anybody experiencing night during the lunar eclipse (50% of the Earth)

What is a “Supermoon”?

• full moon at perigee

What happens during a solar eclipse?

• Moon orbits around Earth casting its shadow on from Earth - it appears that part or all of the Sun is blocked out

A solar eclipse occurs during a _______.

New Moon

During a total solar eclipse, the Earth moves through…

the Umbra only

What is visible during a total solar eclipse during totality?

• corona (thin, outer gases of the Sun)

Annular Solar Eclipse

• Earth moves through the Penumbra, but the Umbra’s shadow does not reach the Earth

When is a solar eclipse Annular?

• when the Moon is farthest from the Earth (apogee) and the Sun is close (perihelion)

What percentage of Earth can see a Total Solar Eclipse?

1%

If you are in the _________ shadow, you can only see a partial eclipse.

• Penumbra’s

NOTE

During a partial eclipse, people a few miles away can see a total eclipse.

Why do we have tides?

• gravity

If mass increases, then…

gravity increases

If distance increases, then…

gravity decreases

The gravity of the Moon + Sun pull on…

the Earth’s oceans

What exhibits the most “tidal force”?

the Moon

What percentage of the Moon + Sun exhibit tidal force?

• Moon: 55%

• Sun: 45%

Why does the Moon exhibit more tidal strength than the Sun?

• closer proximity of objects (distance) exhibits a stronger gravitational force than mass does!! *Moon is closer to Earth than the Sun

How many low tides and high tides occur every 24 hours?

• 2 low tides

• 2 high tides

How often do tides change?

• every 6 hours

A “tidal change” is…

12 hours

What phases do normal tides occur in?

Gibbous + Crescents

What phases do spring tides occur in?

New + Full

What phases do neap tides occur in?

1st + 3rd Quarter

Normal Tides

• crescent + gibbous

• Average - avg. high tides and avg. low tides

Spring Tides (New Moon)

• extreme tides: high tides are very high, low tides are very low

• back side bulge a result of Centrifugal force

• gravitational pull of Moon + Sun are combined

• greatest tidal ranges

Spring Tides (Full Moon)

• extreme tides: high tides are very high, low tides are very low

• gravitational pull of Moon + Sun are combined

• greatest tidal ranges

Neap Tides

• 1st + 3rd Quarter Moons

• Moderate Tides - lower high tides and higher low tides

• Sun + Moon work against each other at right angles, canceling bulge

• small difference between tides