Eclipses

Eclipses are named after the object that “disappears”

Lunar eclipse:

Solar eclipse:

Moon “disappears”

Sun “disappears”

Geometry: Sun – Earth – Moon

Geometry: Sun – Moon– Earth

Lunar Eclipses

Lunar eclipses occur when the Moon enters the shadow of the Earth

The Earth’s shadow has 2 parts:• Umbra – all sunlight blocked• Penumbra – only some sunlight blocked

3 types of lunar eclipses:• Total – all of Moon in umbra

• Partial – only part of Moon in umbra

• Penumbral – Moon only in penumbra

TPS Question

Who can see Lunar Eclipses?

a) Anyone on Earth’s day sideb) Anyone on Earth’s night sidec) Anyone near the Earth’s equatord) Anyone at all

Anatomy of a Lunar Eclipse

Lunar Eclipse

Solar Eclipses

Solar eclipses occur when the Earth enters the shadow of the Moon (the Moon blocks the Sun).

Moon and the Sun have approximately the same (apparent) angular size (1/2 degree).

Sometimes the Moon doesn’t cover the whole Sun and we get an annular eclipse.

The Moon’s shadow also has 2 parts:

•Umbra – all sunlight blocked

•Penumbra – only some sunlight blocked

3 types of lunar eclipses:

• Total – Sun completely covered by Moon

• Partial – Only part of the Sun covered by Moon

• Annular – Some sunlight gets around edge of Moon

TPS Question

Who can see total Solar Eclipses?

a) Anyone on Earth’s night sideb) Anyone on Earth’s day sidec) Anyone near the Earth’s equatord) Only people along a certain path

Anatomy of a Solar Eclipse

Solar EclipseMoon is between Earth and Sun

Solar Eclipses

Solar eclipse is partial when only part of Sun is blocked, total when it all is, and annular when Moon is too far from Earth for total

Solar Eclipse Movie

Eclipse Frequency

Why isn’t there a lunar eclipse during every full moon?

Why isn’t there a solar eclipse during every new moon?

Because the Moon’s orbit around the Earth is tilted.

The Line of Nodes

New Moon – Solar Eclipse

Full Moon – Lunar Eclipse

When the Moon is in the plane of the ecliptic, eclipses can occur.

When the Moon is off the plane of the ecliptic, no eclipses can occur.

New Moon, but no Solar Eclipse

Full Moon, but no Lunar Eclipse

Eclipse FrequencyEclipses don’t occur every month because Earth’s and Moon’s orbits are not in the same plane

Number of eclipses per year:• Solar – at least 2, no more than 5

• Lunar – maximum is 3

• Combined -- maximum is 7

Maximum duration of eclipses:• Solar – 7 ½ minutes

• Lunar – 1 hour, 47 minutes

Eclipse tracks, 2000 - 2020

Tides

Gravity: The Moon pulls more on the near side of the Earth than the far side.

TidesAs a result, water in the oceans is at “high tide” twice a day. Once on the near side to the Moon and again on the far side from the Moon.

At what lunar phase would the variation between high & low tides be greatest?

TPS Question

a) new moon

b) full moon

c) third quarter moon

d) both new and full moon

At what lunar phase would the tidal variation be greatest?

TPS Question

At new & full moon phases, the Sun and Moon combine to stretch the Earth and its oceans even more.

We see higher high tides and lower low tides.

a) new moon

b) full moon

c) third quarter moon

d) both new and full moon

The Sun can also cause tides, but only half as strong as the Moon.

Spring tide – when the tides from the Sun and the Moon combine

Neap tide – when the tides from the Sun and the Moon counter-act each other.

Spring and Neap Tides

The Sun has less effect, but it does modify the lunar tides:

Spring and Neap Tides

Synchronous Rotation

The Moon’s near side is always towards the Earth.