Astronomical ObservationsEclipses

Information About Eclipses

• Definition• Schedule• Terms• Reasons

Moon Orbit and Rotation

Lunar Month vs. Sidereal Orbit

Definition of an Eclipse

• Solar Eclipse– the moon interrupts light from the sun

• Lunar Eclipse– the earth interrupts light shining on the moon

Size of the Shadows

• Solar Eclipse– Sun 400x Larger than Moon, but is also 400x

Farther away– Moon and Sun seem similar size when aligned, so

the Moon can obscure the sun

• Lunar Eclipse– Earth’s shadow blocks sunlight on the Moon

Terms

• Umbra and Penumbra• Total and Partial• Annular• Node

Terms

Frequency

• Lunar Eclipses – occur every 6 months, and total lunar eclipses normally

come in sets of three, followed by three partial eclipses. The total eclipse can last from a few minutes to several hours.

• Solar Eclipses– can occur two to five times a year, but the majority are

partial eclipses. – Total eclipses occur about once every 18 months, and affect

a very limited area. The maximum coverage of the solar disk lasts between 6 and 7.5 minutes.

Schedule• In 2014 there are two solar and two lunar eclipses:

– 2014 Apr 15: Total Lunar Eclipse– 2014 Apr 29: Annular Solar Eclipse– 2014 Oct 08: Total Lunar Eclipse– 2014 Oct 23: Partial Solar Eclipse

• Eclipses can only occur during a “Full Moon” (lunar) or a “New Moon” (solar)

• Why do you think there aren’t 12 solar and 12 lunar eclipses per year?

The Moon’s orbit is not always on the Ecliptic Plane

http://www.astrologyclub.org/articles/nodes/nodes.htm

Annular Eclipses: The Moon’s orbit is not perfectly circular

NASA Eclipse Website

http://eclipse.gsfc.nasa.gov/OH/OH2011.html

A Final Tidbit:Why a Total Lunar Eclipse is Red

Summary – 3 types of Solar eclipses

Summary – 3 types of lunar eclipses

Quiz• Definition – Lunar / Solar• Schedule – How Often• Terms – Umbra, Penumbra, Total, Partial,

Annular, Node• Reason for frequency – planes of orbit (nodes)• Reason for Annular – aphelion vs. perihelion

• Question – Why do more people see lunar eclipses than solar eclipses?