What Causes Eclipse? The Earth and Moon cast shadows. When either passes through the other’s shadow, we have an eclipse. Penumbra is partially illuminated Umbra is completely dark

When can Lunar eclipses occur? A Lunar eclipse happens when the Moon is in the shadow of the Earth Lunar eclipses can occur only at full moon. Lunar eclipses can be penumbral, partial, or total.

Penumbral: Moon passes through the penumbra. Total: all of the Moon passes through the umbra. Partial: only part of the Moon passes through the umbra eastward

When can Solar eclipses occur? A Solar eclipse occurs when the shadow of the Moon falls on the surface of Earth –Only people in the shadow see the eclipse Solar eclipses can occur only at new moon. Solar eclipses can be partial, total, or annular. If you are in the penumbra of the shadow of the Moon

Total and Ring Solar Eclipse What’s the difference between a total and ring eclipse? You see the whole Sun outside of the shadow You see the partial Sun if you are in the penumbra You don’t see the Sun at all if you are in the umbra Moon Surface of the Earth Sun

The Moon’s shadow on the surface of The Earth

Multiple Exposure Photograph of Progression of a Solar Eclipse Totality- lasts only a few minutes. The Solar Corona becomes visible.

Ring Eclipse Ring eclipse is when the Moon does not completely occult the Sun like partial eclipse Ring eclipse occurs when the Sun is too close to the Earth You see the whole Sun if you are outside of the shadow You see the partial Sun if you are in the penumbra You see a ring if you are in here Moon Surface of the Earth Sun

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. The distance between the Moon and Earth changes…this is why we have total and ring eclipses

Solar Eclipses: A Coincidence? What if the Moon is closer (say twice as close) to the Earth? What if the Moon is farther (say twice as far) away from the Earth? What if the Moon is two-times bigger? What if the Moon is two-times smaller?

How Often Does Eclipse Occur? Do we have one solar and one lunar eclipse every month, since we have a full and a new Moon every month?

The Tilt of the Orbit w.r.t the Ecliptic We don’t have a solar and a lunar eclipse every month because the plane of rotation of the Moon around the Earth is tilted about 5º with respect to the ecliptic plane. Eclipses happen only when the nodes of the lunar orbit, the Moon, and the Earth can be connected by a straight line

How Often Does Eclipse Occur? Do we have one solar and one lunar eclipse every six month, when the nodes line-up with the Earth-Moon line? Nodes: the two points when the Moon crosses the ecliptic plane

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

How Often Does Eclipse Occur? The combination of these motions of the Moon 1.29 ½ day orbital motion around Earth, 2.5.2º tilt of the orbit relative to the ecliptic, and 3.Precession of the lunar orbit relative to the ecliptic, Eclipse occurs with a period of about 18 years 11- 1/3 days  Soras cycle But these eclipses don’t happen at exactly the same location over the Soras cycle…

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.

Eclipses: Summary The party involved: Sun, Moon, Earth Motion of the Moon around Earth: 1.29 ½ day revolution of the Moon around the Sun 2.Tilt (~5º) of the lunar orbit (around the Earth) w.r.t. the Ecliptic plane (Earth’s orbital plane around the Sun) 3.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. Lunar eclipse happens when Earth is between the Moon and the Sun.