Presentation on theme: "Earth -Moon Scale and Orbit"— Presentation transcript:
1Earth -Moon Scale and Orbit This powerpoint compiled by the Education Staff at the Lunar and Planetary InstituteImage fromEight days after its final encounter with the Earth, the Galileo spacecraft looked back and captured this remarkable view of the Earth and Moon. The image was taken from a distance of about 6.2 million km (3.9 million miles). The picture was made with images taken through the violet, red, and 1.0-micron infrared filters. The Moon is in the foreground, moving from left to right. The brightly-colored Earth contrasts strongly with the Moon, which reflects only about one-third as much sunlight as the Earth. Contrast and color have been computer-enhanced for both objects to improve visibility. Antarctica is visible through clouds (bottom). The Moon's far side is seen; the shadowy indentation in the dawn terminator is the south pole Aitken Basin, one of the largest and oldest lunar impact features.By the Lunar and Planetary InstituteFor use in teacher workshops
2Earth’s Moon What’s the Moon like? What do people see when they look at the Moon?
3High resolution versions of this image are available atEarly observers thought the dark plains on the Moon were seas and lakes and gave them names like Mare Tranquillitatis (Sea of Tranquillity, where Apollo 11 landed). We retain those traditional names even though, of course, we know they are not seas.In the 1600's, the Italian astronomer Giovanni Riccioli began the custom of naming craters on the Moon for great astronomers. A large crater was later named for Riccioli himself. There's almost a perverse, inverse relationship between the size of a crater and the astronomer's contribution to lunar studies. Great as Plato, Tycho, and Copernicus are, they did not advance our understanding of the Moon much, but they have some of the largest and most conspicuous craters named for them. (By the time telescopes were powerful enough to allow serious research on the Moon, all the good craters were taken!)
4How Big is the Moon?First View of Earth from Moon Date: The world's first view of Earth taken by a spacecraft from the vicinity of the Moon. The photo was transmitted to Earth by the United States Lunar Orbiter I and received at the NASA tracking station at Robledo De Chavela near Madrid, Spain. This crescent of the Earth was photographed August 23, 1966 at 16:35 GMT when the spacecraft was on its 16th orbit and just about to pass behind the Moon. Image Credit: NASA
5Moon Size ~ 1/4 width of Earth Radius of 1080 miles Gravity ~1/6 of Earth’sEarth’s radius = 6378 kilometers or 3963 milesMoon’s radius = 1738 kilometers or 1080 milesEarth image from
6Relative Size and Distance of Earth and Moon? FromThis is what Earthrise looked like from lunar orbit during the Apollo 11 mission. One of the reasons for studying the Moon is to understand more about the origin and geologic history of the Earth. The Moon provides information about how Earth formed, about its initial state, and about its bombardment history. This information has been erased from Earth by billions of years of mountain building, plate motions, volcanism, weathering, and erosion. (AS )Relative Size and Distance of Earth and Moon?
7Earth and Moon to ScaleFromThis 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 atennis ball,23.5 feet away
8Moon Stats No light of its own!! The Moon produces no visible light of its ownIt shines only by reflected sunlightSurface is very dark, only ~7% reflective
9Moon Rotation Spins on axis (rotates) once every 27.3 days Tilted ~1.5 degrees(Earth = 23.5)Moon’s orbit around the Earth is elliptical:~0.15% out of circular.Its orbit is tilted by 5º from the Ecliptic.Mean Distance: 384,400 kmPerigee (Closest Approach): 363,300 kmApogee (Maximum Distance): 405,500 kmAppears ~11% larger at Perigee than at Apogee
10Moon’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: NASA360,000 km ,000 km224,000 miles ,000 miles
11The 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 sideThe Near SideThe NEAR sideThere is NO DARK SIDEThere 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 EarthFar Side: hemisphere facing away from the EarthThe 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.]
12And the Backside! The FAR side FromNo 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.
13Moon StatsMoon’s orbit around Earth is inclined about 5 degrees to Earth’s plane of orbit around the SunEcliptic planeMoon’s orbital planeMoonEarthSunMoon’s orbit around the Earth is elliptical:~0.15% out of circular.Tilted by 5º from the Ecliptic.Mean Distance: 384,400 kmPerigee (Closest Approach): 363,300 kmApogee (Maximum Distance): 405,500 kmAppears ~11% larger at Perigee than at ApogeeUnderstanding 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