Eclipses

"Here lie the bodies of Ho and Hi,Whose fate, though sad, is risible;Being slain because they could not spyTh' eclipse which was invisible."

Author unknown: Said to refer to the Chinese eclipse of 2136 BC or 2159 BC.

"On the day of the new moon, in the month of Hiyar, the Sun was put to shame, and went down in the daytime, with Mars in attendance."

One of the earliest written records of an eclipse of the Sun, on 3 May 1375 BC, found in the city of Ugarit in Mesopotamia.(Reprinted, from Chasing the Shadow, copyright 1994 by Joel K Harris and Richard L Talcott, by permission of Kalmbach Publishing Co.

"If the Sun at its rising is like a crescent and wears a crown like the Moon: the king wll capture his enemy's land; evil will leave the land, and (the land) will experience good . . . "

Refers to a solar eclipse of 27 May 669 BC.Rasil the older, Babylonian scribe to the king.Quoted in Historical Eclipses and Earth's Rotation, by F Richard Stephenson, Cambridge University Press, 1997, page 125.

"Nothing can be surprising any more or impossible or miraculous, now that Zeus, father of the Olympians has made night out of noonday, hiding the bright sunlight, and . . . fear has come upon mankind. After this, men can believe anything, expect anything. Don't any of you be surprised in future if land beasts change places with dolphins and go to live in their salty pastures, and get to like the sounding waves of the sea more than the land, while the dolphins prefer the mountains."

May refer to a total solar eclipse of 6 April 648 BC. Archilochus, Greek poet (c680-640 BC) Quoted in Historical Eclipses and Earth's Rotation, by F Richard Stephenson, Cambridge University Press, 1997, page 338. Partly quoted in Encyclopaedia Britannica CD 98.

ECLIPSE QUOTES

Eclipses

• The Sun and Moon occasionally line up perfectly

Although the Sun is about 400 times larger than the Moon, it is also

about 400 times further away.

As a result of this coincidence, the Moon can completely cover the Sun, producing an eclipse

The shadow of any body consists of two

parts:

The umbra is where the Sun is completely

blocked from view.

The penumbra is where the Sun is only

partially blocked.

Moon's shadow on Earth taken by French cosmonaut Jean-Pierre Haigneré aboard the Mir

Solar Eclipses• When the Moon’s shadow covers part of the Earth• Only happens at New Moon• Three types: Annular, Partial, and Total

Solar Eclipse Factoids

• Under the most favorable conditions, thediameter of the shadow (umbra) is only 269 km wide (155 miles).

• At the equator, the shadow moves at 1730 km/hr.

• Totality can last as long as 7½ minutes.• A total solar eclipse occurs about once every

18 months somewhere in the world.• At any given location, a total solar eclipse

occurs once every 360 years.• Sun’s corona is visible.

Total Solar Eclipse• Observers in the umbra shadow see a total eclipse (safe to

view the Sun)• Those in penumbra see a partial eclipse—not safe to look

directly at Sun

Umbra and Penumbra During Solar Eclipse

Frequency of Solar Eclipses

• We do not get solar eclipses at every newmoon because the orbit of the Moon is tiltedby about 5 degrees with respect to theecliptic.

• At most new moons the Moon is either above orbelow the Sun.

• The tilted orbit of the Moon crosses the ecliptic attwo points. When the Sun approaches thesepoints, eclipses are possible. This will happentwice a year.

Line of Nodes

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 (at or near Apogee)• Sun appears as a donut around the Moon

Annular Eclipse

Photos of an Annular Eclipse

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

When the moon passes through Earth’s shadow.

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

• Who on Earth will be able to see a lunar eclipse?

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

Why is the Moon red during an eclipse?

• The Earth’s atmosphere filters some sunlight and allows it to reach the Moon’s surface

• The blue light is removed—scattered down to make a blue sky over those in daytime

• Remaining light is red or orange• Some of this remaining light is bent or

refracted so that a small fraction of it reaches the Moon

• Exact appearance depends on dust and clouds in the Earth’s atmosphere

Upcoming EclipsesWill we observe these events?• Full Lunar Eclipse Dec. 10th, 2011: No• Annular eclipse of sun May 20: No (West Coast of US

will see it)• Transit of Venus June 5th/6th, 2012: Partial View• 2 other lunar eclipses 2012 (June 4, Nov 28): No

• Next Total Solar Eclipse in USA—August 21, 2017

• Next Total Solar Eclipse in USA visible in Vermont…April 8th, 2024!! Mark your calendars!