General Astronomy Earth and Moon

The Double Planet The 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 Parameters Before 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 3 rd Law) the mass, then we can get the density. Some densities: (in grams/cubic centimeter) Pure Water1.0 Ice0.917 Most Minerals2.5 – 4.0 Iron7.9 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 poles Physical Parameters Albedo - The amount of light reflected from the surface expressed as a fraction; eg, 100% reflection =

Earth Physical Characterstics Radius6,371 Km Density5.52 g/cc Rotation23 h 56 m 04 s Inclination0º Obliquity23º 27' Oblateness1/298.2 Albedo0.39 Escape Vel.11.2 Km/s

The Moon Physical Characteristics Radius1,738 Km Density3.34 g/cc Albedo0.12 Escape Vel.1.9 Km/s

Lunar Features

The Far Side It'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 H 2 O. Big implications for space exploration.

Lunar Water – Sept 2009 NASA'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

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

Buzz Aldrin (photo by Neil Armstrong)

Retroreflector Left 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 2 nd 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 Moon Myths

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

Earth-Moon Interactions Obvious interactions we must examine are: 1.Phases of the Moon (Reprise) 2.Eclipses 3.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

Waxing Crescent First Quarter Waxing Gibbous Full Waning Gibbous Last Quarter Waning Crescent New Lunar Phases Lunar or Synodic Month: 29 1/2 days

The Earth's Shadow The 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

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 Eclipse At 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 Eclipse If you are in the umbra, you see a Total Eclipse

Example of a Solar Eclipse Path

Total Solar Eclipse of 21 June 2001 from Zimbabwe 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

Eclipses So 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° inclination This means that most times it misses the Earth's shadow – too high or too low

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

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

XNoon: High Tide X 6PM MidTide X 6AM MidTide X Midnight: Low Tide One High tide per day? That can't be right! Noon6AMMidnight6AM Tides

X Noon: High Tide X 6PM LowTide X 6AM LowTide X Midnight: High Tide Noon6PMMidnight6AM 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 as Neap Tides

Tides Now 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, Canada At 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 Effects The 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 Belts These 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 Hole Ozone (O 3 ) 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 Interior Seismology- Study of how earthquake vibrations propagate through the Earth’s interior. 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 Earth Formation of topographic relief –Volcanism –Tectonism –Impacts Leveling of the Earth’s surface –Gradation Continental Drift

The Earth at Night