Solar EclipsesHow, why, where, and when solar an lunar eclipses occur.

Eclipse BasicsThe Sun, Moon, and Earth line up so a shadow is cast.

Eclipse PathThe rotation of the Earth and the orbit of the Moon cause the eclipse shadow to follow a linear path on Earth.

Eclipse DurationLongest total eclipse 7:31 m:ssLongest annular eclipse 12:30Longest eclipses in the 20th century 3June 1937 7:04June 1955 7:08June 1973 7:04Number of total eclipses longer than 7 minutes in the 21st century 0

Angular SizeWin a few friendly bets Ask a friend:What matches the size of the moon at arms length? A pea a grape, an orange or a dime?What is the size of the sun? Most astronomers know that the sun & moon are about a degree in angular size. Many people, including astronomers are astounded at just how small that is.

Amazing Coincidences PAST: The moon was closer to the Earth than it is now. The moons shadow would have been wider and the prominences would not have been visible.Present:If the Moon were only 161 miles smaller we could never see a total solar eclipse.If the Moon had a circular orbit at its current average, we could not have total solar eclipses.Future:The moon will continue to move away from the Earth.In the distant future, no total eclipses will be visible.

Eclipse Types Total Eclipses

Eclipse Types Annular Eclipses

Eclipse Types Combination Eclipse

Eclipse Effects Baily's beadsNamed after Francis Baily, the 18th century English amateur astronomer who was the first to draw attention to them. The beads are actually the last few rays of sunlight shining through valleys on the edge of the Moon. Baily's beads make their brief appearance up to 15 seconds before totality.

Eclipse Effects Shadow BandsAs totality approaches, thin wavy lines of shadows appear. These shadow bands are the result of sunlight being distorted by irregularities in the Earth's atmosphere.

Eclipse Effects Diamond RingThe diamond ring effect is the last bit of surface brilliance showing through a lunar valley. This effect lasts for only a few seconds. Once the diamond ring disappears, it is safe to view the sun without a filter.

Eclipse Effects - CoronaAs the moon fully covers the sun and blocks the brilliance of the surface, viewers can see the outer atmosphere, called the corona.

Why dont we have monthly Solar & Lunar eclipses?The moons orbit is inclined 5 to Earths orbit.At two points (nodes) in the Moons orbit, the Sun, Moon, and Earth line up for an eclipse.

Eclipse Mechanics - NodesAn eclipse can happen only within 15.33 of the node, for a total of 30.66 of an eclipse season.Traveling at 1 a day, the sun is in the danger zone for about 30 days. Add up to 7 days for differences in angular sizes of the moon and sun.

Eclipse Mechanics - NumbersOne solar eclipse must occur each eclipse season, giving two eclipses per year.*A lunar eclipse follows a solar eclipse by about 14 days. Most are penumbral and are not visible to the naked eye.If an eclipse happens one or before Jan 18, you could have five eclipses in a single year Solar eclipses in Jan, July, and DecLunar eclipses in Jan and July.* Both may be partial.

Orbital Rhythms Eclipse Seasons

Moving NodesBecause the eclipse year (346.62 days) is shorter than the tropical year (365.26 days), the eclipse season arrives 20 days earlier each year.

Whats a Saros?Eclipses repeat in patterns, bringing similar sets of eclipses to similar regions.6,585 days = 18 years and 11 daysThe difference in timing (partial days) cause the pattern to move westward 1/3 of the Earths surface for each repetition.

239 Anomalistic Months27.55455 days6585.54 days223 Synodic Months29.5306 days6,585.32 days19 Eclipse years346.6201 days6,585.78 days

20th Century Saros 136 Eclipses

Saros DevelopmentEach saros starts with a very brief and partial eclipse of the sun.In 6,585.32 day cycles, a repetition of the eclipse (displaced) brings larger partial eclipses until the moon crosses the center.The pattern repeats, except its now fading.After 13,000 years, the moon no longer eclipses the sun on the predicted date.

Orbital Rhythms Long period

ResourcesTotality: Eclipses of the Sun 1991, Littman and Willcoxhttp://www.mreclipse.com, Fred Espenak http://sunearth.gsfc.nasa.gov, Fred Espenakhttp://www.spaceweather.com NASAhttp://www.earthview.com Bryan Brewerhttp://science.nasa.gov/ NASA

At the most basic, a solar or lunar eclipse happens when the Earth, Sun, and Moon all line up so a shadow is cast on another body. Thats all you need to know to enjoy an eclipse, but there is lots more to it.Reminder:Solar eclipses = new moonLunar eclipses = full moonThe answer is a pea!Most people believe that the sun is larger, but they must be the same if an eclipse can happen.The brilliance makes it seem much, much larger than it really is.

161 miles smaller in diameter Moon is 2176 miles in diameter

Umbra reaches the Earth, follows a curved path.Umbra totalityPenumbra partial eclipseAntumbra (jokes?) The shadow on the Earth that forms the annular eclipse is called Antumbra.Umbra (central shadow)Penumbra (grey shadow)When the Moon approaches these nodes, we can have an eclipse.Reminder A lunar eclipse always follows a solar eclipse, though most of them are not noticeable.The sun moves 1* per day, the moon moves 13* per day.Synodic-Draconic differences Earths orbital speedEclipse year vs tropical year Earths orbital speed20 days earlier each yearAnomalistic Months Moon perigee to perigeeSynodic Months full moon to full moonEclipse years two eclipse seasons moon in ascending or descending nodesEach eclipse was repeated 1/3 of the globe to the west.