Motions of the Sky

1. Seasons2. Tides3. Moon Orbit/Tidal Locking5. Moon Phases6. Lunar Eclipses7. Solar Eclipses8. Planet Retrograde Motion

Rotation –Spinning of the earth on its axis 24 hours 1 day

Revolution- movement of earth around the sun 365 days 1 year

Precession – wobble of earth on axis 26,000 years

Seasons

•Seasons ARE NOT caused by the changing distance between the Sun and Earth.

• During the Northern hemisphere winter, we are actually CLOSER to the Sun.

Seasons ARE caused by:•The TILT of the Earth's axis.•The Earth is tilted 23.5 degrees

Seasons

When it is summer in one hemisphere, it iswinter in the other.

Apparent motion of the Sun

• we do not perceive the Earth moving (Instead the sun appears to move.)

•Ecliptic – The apparent path of the sun

Summer more direct sunlight,

sun appears to be higher in the sky. Higher on the ecliptic

Winter less direct sunlight

sun appears to be lower in the sky. Lower on the ecliptic

spring and fall we get equal light as the opposite

hemisphere. (The sun in on the celestial equator).

Therefore, the seasons are determined by the suns position on the ecliptic.

SeasonsSummer Solstice - June 21 - 22. The sun is at the highest point along the ecliptic. The first day of summer and longest day of year.

SeasonsSummer Solstice - June 21 - 22. The sun is at the highest point along the ecliptic. The first day of summer and longest day of year.

Fall (Autumnal) Equinox - Sept. 22 - 23. The sun crosses the celestial equator heading south. The first day of fall. Equal length of day and night.

SeasonsSummer Solstice - June 21 - 22. The sun is at the highest point along the ecliptic. The first day of summer and longest day of year.

Fall (Autumnal) Equinox - Sept. 22 - 23. The sun crosses the celestial equator heading south. The first day of fall. Equal length of day and night.

Winter Solstice - Dec. 21 - 22. The sun reaches the lowest point on the celestial sphere. The first day of winter and the shortest day of the year.

SeasonsSummer Solstice - June 21 - 22. The sun is at the highest point along the ecliptic. The first day of summer and longest day of year.

Fall (Autumnal) Equinox - Sept. 22 - 23. The sun crosses the celestial equator heading south. The first day of fall. Equal length of day and night.

Winter Solstice - Dec. 21 - 22. The sun reaches the lowest point on the celestial sphere. The first day of winter and the shortest day of the year.

Spring (Vernal) Equinox - March 20 - 21. The sun crosses the celestial equator heading north. The first day of Spring. Equal length of day and night.

Seasons

Earth/Moon System

Scale Diagram of Earth/Moon System

What causes tides?:Just as the Earth pulls the Moon, the moon also

slightly pulls on the Earth.

Tides Basics:

Tides: -The moon pulls on everything on Earth.

-since water is fluid, the Earth cannot hold onto it and the moon is able to pull on it. -This creates two tides per day.

(The continents are also pulled, but much less so, only about30 cm. This is not noticeable)

Tides:

Tidal forces created by one large body on another

Sun Tides:Tides Caused by the Sun:

The Sun is also pulling on the Earth, causing tides,but to a much smaller extent

Spring Tides -When the Sun and Moon align, and the gravitational pull combine, we get extra high tides.

Neap Tides:Neap Tides -When the Sun and Moon are at right angles, the gravitational pull cancels, and we get extra small tides.

Tides:

The Bay of Fundy between Nova Scotia and Main hasthe worlds most extreme tides. Tides can raise and

lower by 48 feet.

http://www.youtube.com/watch?v=_J2AtORivSY

http://www.youtube.com/watch?v=SOAKZLwHhXU

http://www.youtube.com/watch?v=ycNzUAp6OXk

Tides:

Tides:Tidal forces causes

1.The Rotation of the Earth to slow down. 1. (This Causes Precession)

Length of day = 6 hrs 4.5 billion years ago (formation of Earth)Length of day = 20 hrs 300 Million years ago (Devonian time period)Length of day = 23 hrs 80 million years ago (Cretaceous - Dinosaurs)

2. The moon to drifting away.It drifts away 4 cm a year, which is slowly increasing the length of the month.

(Verified by Mirrors placed on Moon during Apollo Missions)

3. Tidal Locking.

Tidal Locking (Phase Locking)

Tidal Locking (Phase Locking)Tidal Locking:Although the moon rotates AND revolves, people on Earth only see 1 side of the moon.

Tidal locking causes 1 rotation of the moon to be equal to 1 revolution of the moon

(1 rotation = 1 revolution)..

Tidal Locking (Phase Locking)

Tidal Locking (Phase Locking)Tidal locking is normal. Objects that are tidally locked:

Moon to EarthPhobos and Deimos to MarsMost of Jupiter and Saturn's Moons.Pluto and CharonProbably Neptune's and Uranus's moons (not enough data)Mercury to the Sun

The moons orbit is not circular, it is elliptical.

This means the moons distance from earth changes over the course of a month.

Moon DistancePerigee vs Apogee

Perigee and Apogee

Moon DistancePerigee vs Apogee

Scale diagram of Earth/Moon system

The Moon at Perigee and Apogee

Perigee - The moons closest approach to earth. (356,000 km)

Apogee - The moons farthest distance from earth. (407,000 km)

Moon Phases

Moon Phases

Caused by: the angle at whichwe view the moon as it orbits the Earth.

Moon PhasesWhat is happening:

-The sun always shines on 1/2 of the moon.

- Depending on the angle at which we see the moon, we see different parts of the moon lit up at different times.

Moon Phases

Moon Phases

Moon Phases

Lunar Eclipses

Cause of Eclipses

Cause of Eclipses

Lunar Eclipse –

Occurs when the moon passes through the Earth’s shadow.

This only occurs during a FULL moon phase, twice per year.

Lunar Eclipses

Lunar Eclipse TerminologyUmbra – The central, dark, shadow of the Earth.

Penumbra - The outer, lighter, shadow of the Earth.

Lunar Eclipse TerminologyTotal Eclipse - The entire moon enters the Earth’s Umbra.

Partial Eclipse – Only part of the moon enters the Earth’s Umbra.

Lunar Eclipse TerminologyPartial Eclipse Total Eclipse

Why is the moon RED during total lunar eclipses?

-Only light scattered through the Earth’satmosphere strikes the moon. Thisscattered light is red. (same reason why sunsets/rises look red.

Lunar Eclipse Pictures

Lunar Eclipse Pictures

Solar Eclipses

Solar Eclipses

Solar Eclipse Terminology

Solar Eclipse - When the moon passes directly between the Sun and Earth, the moons shadow will strike the Earth.

This only occurs during a NEW Moon phase, approximately twice per year.

Why are Total Solar Eclipses much less common?

Animated Solar Eclipse as seen from Space:

Notice the tiny size of the moon’s Umbra

Solar Eclipses as seen from Space:

Solar Eclipses as seen from Space:

From a weather satellite

Solar Eclipse Terminology

A.Total

B. Annular

C. Partial

Solar Eclipse TerminologyTotal Eclipse - The Umbra of the moon strikes the Earth. Anyone standing in this spot sees the moon completely covering the Sun.

Solar Eclipse TerminologyCorona – The faint outer atmosphere of the Sun. Only visible during Total eclipses.

Antarctic Total Eclipse

Solar Eclipse TerminologyPartial Eclipse – The Penumbra of the moons shadow strikes the Earth. Anyone standing in this Spot sees the moon partially covering the Sun.

Solar Eclipse TerminologyAnnular Eclipse – The moon passes directly in front of the Sun. However, the moon is at Apogee,and looks too small to cover the sun for a Total eclipse.

Solar Eclipse TerminologyRing of Fire – During an Annular eclipse, the sun appears to be a ring surrounding the moon.

Annular Eclipse

Annular Eclipse

Retrograde Motion

Retrograde Motion: Planets generally move from west to east in the sky. Occasionally, a planet will

seem to slow down, stop, and loop backwards for a short time.

Retrograde Motion of Mars

Retrograde Motion

Retrograde Motion: Planets generally move from west to east in the sky. Occasionally, a planet will

seem to slow down, stop, and loop backwards for a short time.

Reason Why:The planet did not physically stop and move

backward. This illusion is created by the fact thatone of the planets passed the other in orbit.

(Similar to passing a car on a highway, the car being passed

appears to move backward)

Retrograde Motion

Retrograde Motion of Venus