astronomy lunar phases eclipses and tides

Eclipses and Lunar Phases

and Tides

http://solarsystem.nasa.gov/multimedia/gallery/Earth_Moon.jpg

What does “Phases of the Moon” mean?

• The positions of the moon, Earth, and the sun cause the phases of the moon, eclipses, and tides.

• The phase of the moon you see depends on how much of the sunlit side of the moon faces Earth.

• The moon does not have it’s own light, it reflects light from the sun. This determines its phase.

Moon Facts• The moon goes through a whole set of

phases about once a month.• The Moon orbit at an angle with respect

to the Earth’s orbit around the Sun

• Rotation : Day :: Revolution : year• Since it takes 27.3 Earth days for the moon to

rotate (day) and 27.3 Earth days for the moon to revolve (year), the day and a year are the same length

New (couple days)

Waxing Crescent (several days)

1st Quarter

Waxing Gibbous (several days)

Full

Waning Gibbous (several days)

3rd Quarter

Waning Crescent (several days)

New

Phases: Observing and Identifying

starchild.gsfc.nasa.gov/docs/StarChild/questions/phases.html

Phases--Causes

• The Sun shines on the Moon. – When the sunlight reflects off the Moon’s

far side, we call it a New Moon– When the sunlight reflects off on the

Moon’s near side, we call it a Full Moon– Between New and Full, we see parts of the

daytime side of the Moon.

Golfball and Blacklight Activity

Eclipses

• The Sun and Moon occasionally line up so that we have an eclipse.

– These eclipses happen every year

– To see a solar eclipse, you need to be on a particular part of the Earth

When the Earth’s shadow covers the Moon, we have a lunar eclipse

Three types of Lunar Eclipses

• Penumbral lunar eclipse—the Moon only passes through the penumbra of Earth’s shadow

• Partial lunar eclipse—part of the Moon passes through the umbra of Earth’s shadow

• Total lunar eclipse—the entire Moon passes through the umbra of Earth’s shadow

Anyone who can see the Moon (anyone who is on the nighttime side of the Earth during the eclipse)

Images from Fred Espenakhttp://www.mreclipse.com/LEphoto/LEgallery1/LEgallery1.html

Solar Eclipses• When the Moon’s shadow covers part of

the Earth• Only happens at New Moon• Three types: Annular, Partial, and Total

Total Solar Eclipse• Observers in the “umbra” shadow see a total eclipse (safe to view the Sun); can

see the corona• Those in “penumbra” see a partial eclipse—not safe to look directly at Sun• Only lasts a few minutes• Path of Totality about 10,000 miles long, only 100 miles wide

Photo of a Total Eclipse

http://sunearthday.nasa.gov/2006/multimedia/gal_008.php

Annular Solar Eclipse• When the Moon is too far to completely cover the Sun—the umbra

doesn’t reach the Earth• Sun appears as a donut around the Moon

Photos of an Annular Eclipse

http://sunearthday.nasa.gov/2006/multimedia/gal_010.php; photos taken by Fred Espenak

Solar and Lunar Eclipses

• Solar Eclipse– A solar eclipse occurs when the moon

passes between the Earth and the sun, blocking the sunlight from reaching the Earth.

• Lunar Eclipse– A lunar eclipse occurs at a full moon when

Earth is directly between the moon and the sun.

Next Total Solar Eclipse in USA—August 21, 2017

What is a tide?

• A tide is the rise and fall of water every 12.5 hours.

• The water rises for about 6 hours and then falls for about 6 hours.

What causes the tides?

• The force of the gravity pulls the moon Earth (especially the water on Earth’s surface) toward each other.

• Tides occur mainly because of differences in how much the moon pulls on different parts of the Earth.

Spring and Neap Tides

• Spring Tides– Once a month, at a new moon, the sun,

Earth, and moon are nearly in a line.– The gravity of the sun and moon pull in the

same direction causing a tide with the greatest difference between low and high tide.

• Neap Tides– Twice a month when the Earth and sun are

at right angles to line between the Earth and moon.

– The sun and moon pulling in these directions causes a tide with the least difference between low and high tide.

At which positions will you find a:A. neap tide?B. Spring tide?

Class Review

• Why does the moon change its phases as the month progresses?

• Why are a day and a year on the moon the same length?