Earth and Moon

Earth and Moon to Scale From http://visibleearth.nasa.gov/view_rec.php?id=1624 This image conveys the distance between Earth and Moon. You can demonstrate a scale model to your audience by providing one of your participants with a tennis ball (Moon) and one with a basketball (Earth).  Ask the audience to determine how far apart the two balls should be about 24 feet. Original Caption Released with Image: 2001 Mars Odyssey's Thermal Emission Imaging System (THEMIS) took this portrait of the Earth and its companion Moon, using the infrared camera, one of two cameras in the instrument. It was taken at a distance of 3,563,735 kilometer s (more than 2 million miles) on April 19, 2001 as the 2001 Mars Odyssey spacecraft left the Earth. From this distance and perspective the camera was able to acquire an image that directly shows the true distance from the Earth to the Moon. The Earth's diameter is about 12,750 km, and the distance from the Earth to the Moon is about 385,000 km, corresponding to 30 Earth diameters. The dark region seen on Earth in the infrared temperature image is the cold south pole, with a temperature of minus 50 degrees Celsius (minus 58 degrees Fahrenheit). The small bright region above it is warm Australia. This image was acquired using the 9.1 µm infrared filter, one of nine filters that the instrument will use to map the mineral composition and temperature of the martian surface. From this great distance, each picture element (pixel) in the image corresponds to a region 900 by 900 kilometers or greater in size or about size of the state of Texas. Once Odyssey reaches Mars orbit each infrared pixel will cover a region only 100 by 100 meters on the surface, about the size of a major league baseball field. If Earth were a basketball, then the Moon would be a tennis ball, 23.5 feet away http://visibleearth.nasa.gov/view_rec.php?id=1624 2

Moon Size ~ 1/4 width of Earth Radius of 1080 miles Gravity ~1/6 of Earth’s Earth’s radius = 6378 kilometers or 3963 miles Moon’s radius = 1738 kilometers or 1080 miles Earth image from http://grin.hq.nasa.gov/IMAGES/SMALL/GPN-2000-001444.jpg http://grin.hq.nasa.gov/IMAGES/SMALL/GPN-2000-001444.jpg 3

Surface of the Moon Maria Highlands Craters

Characteristics of our Moon Gravity is only one-sixth as strong as Earth’s Temperatures can range from 100oC to -170oC No air or liquid water

Rotation and Revolution

Moon Rotation Spins on axis (rotates) once every 27.3 days Tilted ~7 degrees (Earth = 23.5) Moon’s orbit around the Earth is elliptical: ~0.15% out of circular. Tilted by 5º from the Ecliptic. Mean Distance: 384,400 km Perigee (Closest Approach): 363,300 km Apogee (Maximum Distance): 405,500 km Appears ~11% larger at Perigee than at Apogee 8

The Near Side The Moon rotates in 27.3 days. The Moon orbits Earth in 27.3 days. Because the Moon rotates and revolves at the same rate, we only see one side The Near Side The NEAR side There is NO DARK SIDE There is a FAR side…. The Moon's rotation period is equal to its orbital period: The Moon completes 1 rotation about its axis in the same time as it completes 1 orbit around the Earth. As a consequence, the Moon always keeps the same face towards the Earth. Near Side: hemisphere facing towards the Earth Far Side: hemisphere facing away from the Earth The synchronization of the Moon's rotation and orbit is caused by strong tidal forces from the Earth that effectively "locks" the Moon's orientation relative to the Earth. [Note: The degree of synchronization is not perfect for two reasons. First, the Moon's orbit is elliptical rather than circular, so that the Moon's orbital speed is faster at perigee and slower at apogee. This mis-match in the exact orbital and rotation rates results in an apparent east-west "rocking" motion of the Moon by about 7.9 degress over the course of a month. The second is that the axis of the moon's rotation is tilted by about 7 degrees relative to its orbital plane (like the Earth's 23.5 degrees). This leads to an additional north-south nodding motion over the course of a month. The combined rocking and nodding motion motion is called "libration". You can see libration in the lunation movie below.] 9

And the Backside! The FAR side From http://photojournal.jpl.nasa.gov/catalog/PIA00304 No humans had seen this side of the Moon until spacecraft were sent to orbit the Moon. It is markedly different from the side that faces us; it has far fewer maria and is more dominated by the bright highlands and craters. We conduct a couple of activities here on facing the Moon: using the participants to physically model out the motion, and doing the Penny Moon-Quarter Earth activity. About 50,000 Clementine images were processed to produce the four orthographic views of the Moon. Mare Moscoviense (dark albedo feature upper left of image center) and South Pole-Aitken Basin (dark feature at bottom) represent maria regions largely absent on the lunar farside. The Clementine altimeter showed Aitken Basin to consist of a topographic rim about 2500 km in diameter, an inner shelf ranging from 400 to 600 km in width, and an irregular depressed floor about 12 km in depth. http://photojournal.jpl.nasa.gov/catalog/PIA00304 10

Moon’s Orbit Orbits (revolves around) Earth every 27.3 days Elliptical orbit (not a perfect circle) Near and Far The above illustration, based on Galileo spacecraft images, shows the approximate difference in apparent size between a full moon at perigee (the closest point in the lunar orbit, pictured at left) and a full moon at apogee, the farthest point in the lunar orbit. Image Credit: NASA http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=442 360,000 km 406,000 km 224,000 miles 252,000 miles http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=442 11

Moon Stats Moon’s orbit around Earth is inclined about 5 degrees to Earth’s plane of orbit around the Sun Ecliptic plane Moon’s orbital plane Moon Earth Sun Moon’s orbit around the Earth is elliptical: ~0.15% out of circular. Tilted by 5º from the Ecliptic. Mean Distance: 384,400 km Perigee (Closest Approach): 363,300 km Apogee (Maximum Distance): 405,500 km Appears ~11% larger at Perigee than at Apogee Understanding this is fundamental to understanding why eclipses do not happen every month, or getting the reason for phases confused with eclipses. Image created by LPI staff 12

Phases of the Moon Caused by its position relative to the Earth and the sun. 29.5 days from new moon to new moon. The moon rises 50 minutes later each night.

Phases of the moon

Solar and Lunar Eclipses The total or partial obscuring of one celestial body by another… The obscuration can be either One celestial body blocking the view to the other: Solar eclipse---Moon blocking Earth’s view to the Sun… One celestial body is in the shadow of another: Lunar eclipse---Moon is in the shadow of the Earth… Lunar eclipse image from http://www.mreclipse.com

Solar Eclipses The solar corona is revealed during a total solar eclipse The corona is about one millionth times fainter than the disk of the Sun. Similar to observing stars next to the Sun, the light from the disk must be blocked (by the moon, or by special occulter in the telescope) before we can see the solar corona.

What Causes Eclipse? The Earth and Moon cast shadows. When either passes through the other’s shadow, we have an eclipse. Because the Sun is an extended bright object, there are two different regions of the shadow: Penumbra is partially illuminated Umbra is completely dark Click on the image to start animation

Lunar eclipses Lunar eclipses happens when the Moon passes through the shadow of the Earth Everybody on the night side of Earth can see the lunar eclipse. Lunar eclipses can be partial, penumbral, or total. Lunar eclipses can occur only at full moon. Use the interactive figure to show the conditions for the 3 types of lunar eclipse.

Solar eclipses Solar eclipses occur when the shadow of the Moon falls on the surface of Earth Only people in the shadow can see the eclipse. Solar eclipses can be partial, annular, or total. Solar eclipses can occur only at new moon. Use the interactive figure to show the conditions for the 3 types of solar eclipse.

Eclipse Path When total or ring solar eclipse happens… The diameter of the umbra of lunar shadow is no more than 270 km…you can see the total eclipse only if you are in a very narrow and long eclipse path. The diameter of the penumbra of the lunar shadow is about 7000 km (Earth’s diameter is about 13,000 km). So, the region that partial eclipse can be seen is quite large.

Total Solar Eclipse What’s the difference between a total and ring eclipse? The distance between the Earth and the Sun. You don’t see the Sun at all if you are in the umbra Surface of the Earth Sun Moon You see the partial Sun if you are in the penumbra Click on the Sun to start animation You see the whole Sun outside of the shadow

Distance Between the Moon and Earth Like the Earth’s orbit around the Sun, the orbit of the Moon around the Earth is not a perfect circle. Eccentricity of Earth’s orbit is ~ 0.016 The distance between the Moon and Earth change. This is why we have total and ring eclipses Eccentricity of Lunar orbit is ~ 0.05

How Often Does Eclipse Occur? Do we have one solar and one lunar eclipse every month, since we have a full and a new Moon every month?

How Often Does Eclipse Occur? Do we have one solar and one lunar eclipse every six month, when the nodes line-up with the Earth-Moon line? NO! Because of the precession of the lunar orbit! Nodes: the two points when the Moon crosses the ecliptic plane Only when the nodes are located right between the Earth-Sun line can solar eclipses occur.

Solar Eclipse Forecast Solar eclipses from 2004 to 2030 Knowing the orbit of the Earth and the Moon, we can now calculate the time and path of solar eclipses with great accuracy. Back to Eclipse Path

Apollo Moon Missions 1963-1972 Apollo 11, 12, 14, 15, 16, 17 landed humans on the surface of the moon The six missions that landed on the moon returned a wealth of data and 400 kg of lunar samples. Experiments included soil mechanics, meteoroids, seismic, heat flow, lunar ranging, magnetic fields, and solar wind experiments.

Apollo Moon Landings moon landing.asx