1. Eclipses

2. Lining Up At new moon the moon can block the sun.
At full moon the earth can block the sun to the moon.
This is called an eclipse.
Solar eclipse, lunar eclipse

3. Kinds of Eclipses Solar Eclipse Lunar Eclipse Partial - crescent Sun
Moon’s shadow on Earth
Occurs at a new moon
Partial - crescent Sun
Total - all of Sun is blocked
Annular - a ring of the Sun
Lunar Eclipse
Earth’s shadow on moon
Occurs at a full moon
Partial - moon partially dark
Total - moon is dark red or copper-colored
Earths atmosphere passes some light.

4. Elliptical Orbit The Moon has a synodic period of 29.53 days.
the time from new moon to new moon.
The Moon’s orbit is an ellipse.
At the nearest, perigee, the distance is 363,000 km
At the farthest, apogee, the distance is 406,000 km
The period between perigees is days.
This is the anomalistic period.

5. Try It!
Close one eye.
Hold a coin out far enough to completely block the circle.
Move out a little for an annular eclipse.

6. Annular Eclipse May 10, 1994, North Central United States
Photograph by John Chumack

7. Orbital Inclination
The Moon has an elliptical orbit tilted at 5.2° compared to the orbit of the Earth around the Sun.
When the Moon crosses the Sun-Earth plane, it is at a node.
The period between two ascending nodes is days
This is the draconic month.

8. Eclipse Seasons Conditions for a solar eclipse:
New Moon (once every 29.5 days)
Moon at a node (twice every 27.2 days)
The circumstances happen about every 6 months.
May 10, 1994: Annular eclipse in N. America
Nov 3, 1994: Total eclipse in S. America
Eclipse season lasts about one month.

9. Season Duration An eclipse season lasts about a month.
Full moon for lunar eclipse
New moon for solar eclipse
Oct 8, 2014
Oct 23, 2014

10. Saros Cycle Convergence of cycles 223 synodic months is 6585.3 days
So is 242 draconic months, and 239 anomalistic months
Every 18 years, 10 or 11 days, and 8 hours the Earth, Moon and Sun are in the same position.
These cycles were known since antiquity, and used to predict eclipses.

11. Total Solar Eclipse August 11, 1999: Szombately, Hungary
Photographs by Michael Fortner

12. Viewing Eclipses
Never look directly at the sun, even at a partial eclipse.
It’s ok to look at lunar and true total eclipses.
View sun through #14 welder’s glass or special mylar filters.

13. Great American Eclipse
August 21, 2017
Total solar eclipse in a narrow band
Partial solar eclipse outside band