1. Eclipses
Solar and Lunar

2. Solar and Lunar Eclipses
The total or partial obscuring of one celestial body by another…
The obscuration can be either
One celestial body blocking the view to the other:
Solar eclipse---Moon blocking Earth’s view to the Sun…
One celestial body is in the shadow of another:
Lunar eclipse---Moon is in the shadow of the Earth…
Lunar eclipse image from

3. What Causes Eclipse? The Earth and Moon cast shadows.
When either passes through the other’s shadow, we have an eclipse.
Because the Sun is an extended bright object, there are two different regions of the shadow:
Penumbra is partially illuminated
Umbra is completely dark
Click on the image to start animation

4. Lunar eclipses
Lunar eclipses happen when the Moon passes through the shadow of the Earth
Everybody on the night side of Earth can see the lunar eclipse.
Lunar eclipses can be partial, penumbral, or total.
Lunar eclipses can occur only at full moon.
Use the interactive figure to show the conditions for the 3 types of lunar eclipse.
Click on the image to start animation

5. Solar eclipses
Solar eclipses occur when the shadow of the Moon falls on the surface of Earth
Only people in the shadow can see the eclipse.
Solar eclipses can be partial, annular, or total.
Solar eclipses can occur only at new moon.
Use the interactive figure to show the conditions for the 3 types of solar eclipse.

6. Eclipse Path When total or ring solar eclipses happens…
The diameter of the umbra of lunar shadow is no more than 270 km…you can see the total eclipse only if you are in a very narrow and long eclipse path.
In the 1990 total eclipse that passed through the big island of Hawaii, people on Maui and Oahu cannot see the total eclipse!
The diameter of the penumbra of the lunar shadow is about 7000 km (Earth’s diameter is about 13,000 km). So, the region that partial eclipse can be seen is quite large…and people on Maui and Oahu could see partial eclipse!
 Eclipse Prediction

7. Total Solar Eclipse
What’s the difference between a total and ring eclipse?
The distance between the Earth and the Sun.
You don’t see the Sun at all if you are in the umbra
Surface of the Earth
Sun
Moon
You see the partial Sun if you are in the penumbra
Click on the Sun to start animation
You see the whole Sun outside of the shadow

8. Annular Eclipse
Annular eclipse happens when the Moon does not completely block the Sun, like partial eclipses…
The umbra is NOT completely dark!
You see a ring if you are in here
Surface of the Earth
Sun
Moon
You see the partial Sun if you are in the penumbra
You see the whole Sun if you are outside of the shadow

9. Distance Between the Moon and Earth
Like the Earth’s orbit around the Sun, the orbit of the Moon around the Earth is not a perfect circle.
Eccentricity of Earth’s orbit is ~ 0.016
The distance between the Moon and Earth change. This is why we have total and ring eclipses
Eccentricity of Lunar orbit is ~ 0.05

10. How Often Does Eclipse Occur?
Why don’t we have one lunar and one solar eclipse a month since we have one new and one full moon each month?
Click on the image to start animation

11. The Precession of Lunar Orbit
The orbital motion of the Moon around Earth slowly precesses with an 18.6 year cycle as the Earth orbit the Sun…
Click on the image to start animation

12. How Often Does Eclipse Occur?
The combination of these motions of the Moon play a part:
29 ½ day orbital motion around Earth,
5º tilt of the orbit with regard to the ecliptic, and
Precession of the lunar orbit with regard to the ecliptic,
Eclipse occurs with a period of about 18 years and 11-1/3 days (Soras cycle)

13. Solar Eclipse Forecast
Solar eclipses from 2004 to 2030
Knowing the orbit of the Earth and the Moon, we can now calculate the time and path of solar eclipses with great accuracy.
Back to Eclipse Path

14. Eclipses: Summary The parties involved: Sun, Moon, and Earth
Motion of the Moon around Earth:
29 ½ day revolution of the Moon around the Sun
Tilt (~5º) of the lunar orbit (around the Earth) w.r.t. the Ecliptic plane (Earth’s orbital plane around the Sun)
The precession of the lunar orbit w.r.t. Earth-Sun direction
Solar eclipse happens when the Moon is between the Earth and the Sun.
The size and distance of the Moon need to be just right for us to see total eclipse.
The changing distance between the Earth and the Moon explains the occurrences of the total and ring solar eclipses.
The changing distance between the Earth and the Sun, and the Earth and the Moon explains the difference in the duration of the solar eclipses.
Lunar eclipse happens when Earth is between the Moon and the Sun.