General Astronomy

Earth and Moon

The Double PlanetThe Earth-Moon system is unique in this solar system in that

Earth's moon is the largest in relation to its planet.

Earth, Terra, Sol III What's in a name?

Apollo 17

This is where you live.

This is where all of your ancestors have ever lived.

Yours may be the first generation who's children may live elsewhere.

The Moon, Luna, Selene

Taylor Observatory Stockton 5" Celestron

This is where some may live in the future

Physical ParametersBefore comparing the planets, let's look as some of the physical

characteristics:Density – Mass divided by volume

This gives us an idea of the composition of the body. If we can measure the radius and (from Kepler's 3rd Law) the mass, then we can get the density.

Some densities: (in grams/cubic centimeter)

Pure Water 1.0

Ice 0.917Most Minerals 2.5 – 4.0Iron 7.9

Of course, a planet is a mixture – so the actual density depends on how much of each type of item is present.

Obliquity – The 'tilt' of the north-south (rotational) axis with respect to the Ecliptic.

Earth's inclination is 23.5 degrees

Physical Parameters

Inclination – The 'tilt' of the orbit with respect to the Ecliptic

Oblateness - The flattening at the polesPhysical Parameters

Albedo - The amount of light reflected from the surface expressed as a fraction; eg, 100% reflection = 1.0

0.0 .40 .60 1.0

Earth

Physical Characterstics

Radius 6,371 KmDensity 5.52 g/ccRotation 23h56m04s

Inclination 0ºObliquity 23º 27'Oblateness 1/298.2Albedo 0.39Escape Vel. 11.2 Km/s

The Moon

Physical Characteristics

Radius 1,738 KmDensity 3.34 g/ccAlbedo 0.12Escape Vel. 1.9 Km/s

Lunar Features

The Far SideIt's easy to see that the far side of the Moon is much rougher.There are many more impact craters and much fewer marias.

This makes sense when you realize the Earth has been 'protecting' the near side

Ice on the Moon?• A recent mission called Lunar Prospector has

reported possible evidence for ice on the Moon:• The Moon has permanently shadowed polar

craters too.• Data showed slightly enhanced Hydrogen in these

areas.• Not confirmed by radar images as on Mercury.• H could be from solar wind or some other process

and• might not be the "H" in H2O.• Big implications for space exploration.

Lunar Water – Sept 2009NASA's Moon Mineralogy Mapper, an instrument on the Indian Space Research Organization's Chandrayaan-1 mission, took this image of Earth's moon.

It is a three-color composite of reflected near-infrared radiation from the sun, and illustrates the extent to which different materials are mapped across the side of the moon that faces Earth.

Small amounts of water were detected on the surface of the moon at various locations. This image illustrates their distribution at high latitudes toward the poles.

Blue shows the signature of water, green shows the brightness of the surface as measured by reflected infrared radiation from the sun and red shows an iron-bearing mineral called pyroxene.

Lunar Water – Sept 2009

Lunar Water – Sept 2009

On the left is an image showing brightness at shorter infrared wavelengths. On the right, the distribution of water-rich minerals (light blue) is shown around a small crater. Both water- and hydroxyl-rich (red) materials were found to be associated with material ejected from the crater.

Lunar Cratering

Ages of SurfacesDating of Moon rocks allow us to measure when the rock was last melted…

…when were most craters made?

What is the order from oldest to youngest?

A (volcano)

B (crater)

C (crater)D (lava flow from another volcano)

A, C, D, B

Buzz Aldrin (photo by Neil Armstrong)

RetroreflectorLeft on the lunar surface by the Apollo astronauts, this instrument is used to reflect laser beams back to Earth and accurately measure the moon's distance.Hard to do if the Moon landings were a hoax.

• A blue moon is when more than one full moon occurs in the same calendar month. The 2nd occurance is the blue moon• The moon undergoes synchronous rotation and revolution (i.e. the periods of rotation and revolution are identical), so one side of the moon always faces the Earth.

• The harvest moon involves the rising of the full moon in late September and early October.

Moon Factoids

• The phase of the moon has no effect on human behavior.

• There is no such thing as the “darkside of the moon.”

• We did indeed land humans on the moon in the six Apollo landings between July 1969 and December 1972.

Moon Myths

Mythbusters!

There is no relationship between the full moon and the number of births

Earth-Moon InteractionsObvious interactions we must examine

are:

1. Phases of the Moon (Reprise)2. Eclipses3. Tides

N.P. Noon

Sunset

Midnight

Sunrise

New

Sunset

New

Waxing Crescent

Sunset

Waxing Crescent

First Quarter

Sunset

First Quarter

Waxing Gibbous

Sunset

Waxing Gibbous

Full

Sunset

Full

Sunrise

Full

Waning Gibbous

Sunrise

Waning Gibbous

Last Quarter

Sunrise

Last Quarter

Waning Crescent

Sunrise

Waning Crescent

New

Sunrise

New

The Phases

about 1 week for each quarter (like newfirst quarter)

New Waxing Crescent

First Quarter

Waxing Gibbous

Full Waning Gibbous

Last Quarter

Waning Crescent

New

Lunar Phases

Lunar or Synodic Month: 29 1/2 days

Sidereal and Synodic Months

SUN

• synodic month: time for Moon to make one circle of sky compared to Sun

• sidereal month: time for Moon to make one circle of sky compared to stars

SUN

27.3 d 29.5 d

The Earth's ShadowThe Earth will cast two shadows. One where all the light is blocked and a second where only part of the light is blocked

The darker, innermost shadow is the Umbra

The lighter, surrounding shadow is the Penumbra

Shadows

total shadow: UMBRApartial shadow: PENUMBRA

lower edge of Sun blocked from view

upper edge of Sun blocked from view

Lunar Eclipse

Moon

When the Moon enters the Earth's shadow, we have a lunar eclipse

This, of course, can only occur at the time of the Full Moon

Lunar Eclipse

A total eclipse of the moon.

Solar EclipseAt the time of the New Moon, the Moon casts its shadow(s) on the Earth

The Moon's shadows are much smaller and only cover a small area on the Earth. If you are in the penumbra, you see a Partial EclipseIf you are in the umbra, you see a Total Eclipse

EclipsesSo if a Lunar eclipse occurs at a full

moon and a Solar eclipse occurs at a new moon, why don't we see each type of eclipse every month?

Inclination of Orbits

The moon's orbit is a bit over 5° inclinationThis means that most times it misses theEarth's shadow – too high or too low

Eclipses

Earth and lunar shadows, shown at proper scale, illustrate why eclipses occur infrequently.

Path of Totality - 2017

Total Eclipse - 2017Pomona, NJPartial Eclipse

Salem, ORTotal Eclipse

Total Eclipse - 2017Salem, OR

Start of eclipse

Ha

TotalityCrescents through the leaves

Bailey’s Beads

Solar Corona

“Diamond Ring”

The orbits of the moon and Earth are elliptical, which affects the angular diameters of the moon and sun.

An annular eclipse

Lunar Shadow from Mir

Lunar Shadow passing over Africa

The tides are caused by the differential forces of the moon's gravitational pull. The term differential forces implies the differences at varying points on the Earth - it should be clear since gravitational force depend on distance that the force on the point directly beneath the moon will be greater than at any other point. As the Lunar gravity pulls on the water, it flows to that spot as best it can.

The Tides

Tides

Ignoring the actual geography and shape of the Earth this leads to a simple (and incorrect) model of the tides

Why is this incorrect?To see, let's ignore the orbital motions and look at the daily rotation of the Earth

X Noon: High Tide

X

6PM MidTide

X

6AM MidTide

XMidnight: Low Tide

One High tide per day? That can't be right!

Noon 6AM Midnight 6AM

Tides

XNoon: High Tide

X

6PM LowTide

X

6AM LowTide

XMidnight: High Tide

Noon 6PM Midnight 6AM

Tides

• Of course the Tides are more complicated than this simple picture.– The moon also moves in its orbit– Geography becomes a significant

factor– The moon and the earth are inclined

to the ecliptic– The Sun's gravitational pull creates

tides of about 50% of those caused by the Moon

Tides

Adding the Sun's Effects

When the sun and moon are lined up, during a full moon and a new moon, the tides caused by each augment each other giving higher highs and lower lows.

These are known as

Spring Tides

When the moon's direction is at right angles to the sun, the tides tend to cancel each other leading to lower highs and higher lows.

These are known asNeap Tides

TidesNow let's see what 'geography' can do to

the tides.For example, the Delaware River is a tidal

estuary. It takes the tide about six hours to move from the mouth of the Delaware Bay to Philadelphia. So when it's high tide at Cape May, it is low tide at Philly and vice versa.

A more impressive effect, however, is farther north…

Bay of Fundy, NS, CanadaAt low tide, the Bay is an interesting place to walk and explore. Ocean bottom as far as the eye can see…

But, don't wander too far from shore. The tide can rise nearly 17 meters

Tidal Friction• As the oceans are constantly being

pulled about the Earth by Lunar and Solar gravity, there is friction. Where there is friction, there is energy loss resulting in a slowing down of the Earth's rotational speed.

• The days are getting longer increasing by several milliseconds each century

• Since the earth and moon form a system this slowing also affects the moon. The moon is slowly receeding from the earth.

• Eventually, the Earth and Moon will always keep the same face to each other

Magnetic Field EffectsThe Earth's magnetic field is also very

important to those who live on its surface.– The obvious uses for navigation – both for

humans and migrating birds– More importantly, the magnetic field protects

us from the Sun• The Sun is constantly emitting streams of charged

particles (as well as light and warmth)• If all of these were to hit the surface, life would

likely not exist.– The magnetic field forms a protective barrier

trapping much of the oncoming particles and channeling some of the more intense into the north and south poles.

The Magnetosphere

Magnetic Field Effects• As the charged particles (protons, electron and other

ions) follow the magnetic field lines into the poles, they strike atoms in the atmosphere causing them to emit light. This light is known as the aurora– Aurora borealis (Northern Lights)– Aurora austrialis (Southern Lights)

Photos by Jan Curtis, Fairbanks, AK

Northern Lights From Above and Below

Van Allen Radiation BeltsThese are two torus

shaped areas of intense radiation where energetic particles from the sun are trapped by the earth's magnetic field.

The inner belt is about 4,000 miles out, and the outer about 10,000 miles

Note how the sunward side is compressed by the Solar Wind.

The Ozone HoleOzone (O3) absorbs in the ultraviolet and protects us, animals and plants.Clorofluorocarbons (freons) and halons (bromine) when they get into the upper regions of the atmosphere break down and the chlorine and bromine work to reduce the available ozone.

The Earth’s InteriorSeismology- Study of how earthquake vibrations propagate through the Earth’sinterior.

Material of the Earth reflects and bends seismic waves:p – primary waves (longitudinal waves) Propagate through solids and liquids.s – secondary waves (transverse waves) Propagate through only through solids.

Solid inner core, liquid outer core, mantle, crust

Shaping the EarthFormation of topographic

relief– Volcanism– Tectonism– Impacts

Leveling of the Earth’s surface– Gradation

Continental Drift

The Earth at Night