Phases, Eclipses and Tides. Rotation and Revolution It takes the same amount of time for the moon to rotate on its axis as it does to revolve around the.

Phases, Eclipses and Tides

Rotation and Revolution

• It takes the same amount of time for the moon to rotate on its axis as it does to revolve around the Earth (27.3 days)

• This is why the Earth only sees one side of the moon – in order to see the other side you need to get on a space ship and go around the moon

Moon Phases

• Lit by sun• Half of moon always

lit• Phases due to

different amounts of the lit portion of the moon visible on Earth

http://www.astro.virginia.edu

Moon Phases

• The moon rises and sets just like the sun – the position of the moon and time of the moon rise/set changes throughout the month

• New moon rises with the sun

• Full moon rises as sun sets http://radiojove.gsfc.nasa.gov

Eclipses

• Solar eclipse – (new) moon blocks sunlight – Earth is in moon’s shadow – Order: sun, moon, earth

• Lunar eclipse – Earth blocks sunlight from hitting (full) moon – moon is in Earth’s shadow – Order: sun, earth, moon

Shadows• Umbra: darkest part of shadow: this

shadow causes total eclipses

• Penumbra: Outer, less dark shadow

http://www.astronomy.ohio-state.edu

Lunar Eclipse

Solar Eclipse

There are also partial eclipses:

Partial Lunar when part of moon is in umbra (there are also penumbral eclipses)

Partial Solar: seen by anyone in the penumbra

Anyone here would see a total eclipse

Moon

Eclipses• Generally 2 solar and

2 lunar eclipses a year – not always total.

• Area on Earth to see total solar eclipse is very, very small - why seeing one is so rare (rest of Earth able to see anything sees a partial eclipse)

http://oiswww.eumetsat.org

Solar Eclipse

• Last total eclipse = Nov. 13, 2012 in Southern Hemisphere starting in Northern Australia

• Next total eclipse = Mar. 20, 2015 in Northern Hemisphere visible in Iceland, Europe, North Africa, and North Asia

http://www.astro.uva.nl

List of Eclipses

Pictures of Annular Eclipses

http://www.astronomy.comhttp://media.skytonight.com

Occurs when the moon is at a point where it is not big enough to block all of the sunlight: a ring of sunlight is visible

• Last annular – April 25, 2013. The path of the Moon's antumbral shadow began in western Australia , eastern Papua New Guinea, the Solomon Islands and crossed the South Pacific Ocean

• FYI – no true umbra since moon doesn’t completely block the sun. Antumbra extends just beyond the umbra and is similar to penumbra

• Next annular – April 29, 2014. The path of the Moon's antumbral shadow will cross Antarctica

Total Solar Eclipse – you see the Sun’s Corona

http://www.astropix.com

Pinhole effect

This is the "pinhole effect" that happens under a tree during a solar eclipse. See all of the little crescent suns?

Moon’s Shadow on Earth

Lunar Eclipse

• Last total lunar eclipse was on December 10, 2011. Entire event was visible in Asia & Australia. North America could see as moon set in western sky.

.

http://www.jsu.edu

Lunar Eclipse

• Eclipsed moon looks red because some sunlight bends as it passes through Earth’s atmosphere before hitting the moon

• The entire event is visible from both North and South America. Observers in the western Pacific miss the first half of the eclipse because it occurs before moonrise. Likewise most of Europe and Africa experience moonset just as the eclipse begins. None of the eclipse is visible from north/east Europe, eastern Africa, the Middle East or Central Asia.

AND NOW SOME PHOTOS!

http://eclipse.gsfc.nasa.gov/eclipse.html

• Go to the website to learn about past and future eclipses

Tides

• Tides occur because the moon’s gravity does not pull with the same force on all parts of the Earth

http://serc.carleton.edu

High Tides

• Location A: Moon’s gravitational force on the water is greater than its force on the Earth as a whole

• Water here is pulled more towards the moon than the Earth = high tide

A

B

C

D

High Tides

• Location C: The moon’s gravitational force on the Earth as a whole is stronger than its force on the water

• The Earth is pulled more towards the moon and the water is “left behind” = high tide

A

B

C

D

Low Tides

• Locations B and D: Water flows away from these locations towards points A and C = low tide

C

B

D

A

Tides

http://www.huntsmanmarine.ca

High Tide

Low Tide

Every location on Earth has 2 high tides and 2 low tides every 25 hours

Spring and Neap• The Sun’s gravity also pulls on Earth’s

waters

• Sometimes the sun’s and moon’s gravity work together (spring tide) and sometimes they pull on the water in different (perpendicular) directions (neap tide)

• Spring and Neap tides happen twice a month

Spring Tide

• during full and new moons • highest high tides and lowest low tides

http://www.huntsmanmarine.ca

Neap Tide

• Neap tide: during first and last quarter moons

• lowest high tides and highest low tides

http://www.huntsmanmarine.ca