# Geometry: Sun – Moon– Earth

## Presentation on theme: "Geometry: Sun – Moon– Earth"— Presentation transcript:

Geometry: Sun – Moon– Earth
Eclipses Eclipses are named after the object that “disappears” Lunar eclipse: Moon “disappears” Geometry: Sun – Earth – Moon Solar eclipse: Sun “disappears” 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? Anyone on Earth’s day side
Anyone on Earth’s night side Anyone near the Earth’s equator 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?
Anyone on Earth’s night side Anyone on Earth’s day side Anyone near the Earth’s equator Only people along a certain path

Anatomy of a Solar Eclipse

Solar Eclipse Moon 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 Do an in-class demo.

When the Moon is in the plane of the ecliptic, eclipses can occur.
New Moon – Solar Eclipse Full Moon – Lunar Eclipse

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 Frequency Eclipses 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,

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

Tides As 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.

TPS Question new moon full moon third quarter moon both new and full moon At what lunar phase would the variation between high & low tides be greatest?

TPS Question new moon full moon third quarter moon both new and full moon At what lunar phase would the tidal variation be greatest? 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.

Spring and Neap Tides 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:

Synchronous Rotation The Moon’s near side is always towards the Earth.
Moon has become tidally locked to the Earth.