The Moon

1. The Moon Stacy McCormack HST2006 “Discovering the Universe by Looking at the Sky”

2. Questions about the moon • Where did the moon come from? • Why does the moon have “pimples” (craters)? • Why doesn’t the moon crash into the Earth? • Why do we sometimes only see slices of the moon? • Do we only see one side of the moon? • Why can we sometimes see the moon during the day? • What would happen to the Earth if the moon were gone? • What are lunar eclipses?

3. Where did the moon come from? • The Giant Impactor Theory (sometimes called The Ejected Ring Theory) • The basic idea is this: about 4.45 billion years ago, a young planet Earth -- a mere 50 million years old at the time and not the solid object we know today-- experienced the largest impact event of its history. Another planetary body with roughly the mass of Mars had formed nearby with an orbit that placed it on a collision course with Earth. When young Earth and this object collided, the energy involved was 100 million times larger than the much later event believed to have wiped out the dinosaurs! The early giant collision destroyed the object, likely vaporized the upper layers of Earth's mantle, and ejected large amounts of debris into Earth orbit. Our Moon formed then from this debris. • http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question38.html

4. What artists believe the formation of our moon looked like

5. Why does the moon have “pimples” (craters)? • What has created those strange round "craters"? ("Krater" is Greek for a bowl or wide-mouthed goblet.) They reminded some observers of volcanic craters on Earth. Others suggested that they were formed by the impact of large meteorites, but this was countered by the argument that most meteorites probably arrived at a slanting angle, and were expected to leave not a round ring but an elongated oval. • We now know that the impact explanation was right. The craters are round because at the enormous velocities with which meteorites arrive, the impact resembles a local explosion, and the signature of the impact is determined by the energy released rather than by the momentum transmitted. • http://www-spof.gsfc.nasa.gov/stargaze/Smoon2.htm

6. Do we see these “pimples” on Earth? • We do see evidence of these craters on Earth too: Part of the evidence has come from the nicely rounded impact remnants found on Earth, Manicougan lake in Canada, in northern Quebec (picture on left), which is about 100 km (60 miles) wide and 214 million years old. After the impact, the central land rose again to the level of its surroundings, pushed by fluid pressure of the material below it, which acts like a fluid and tries to establish equilibrium between the different loads which it supports. • Picture on right: Barringer Meteor Crater, Arizona. http://www.solarviews.com/eng/tercrate.htm

7. More examples of craters on Earth 1 2 • http://www.solarviews.com/eng/tercrate.htm • 1-Chicxulub, Yucatan Peninsula, Mexico • 2-Aorounga, Chad, Africa • 3-Wolfe Creek, Australia • 4-Roter Kamm, South West Africa/Namibia • 5-Mistastin Lake, Newfoundland and Labrador, Canada • 6-Clearwater Lakes, Quebec, Canada • 7-Deep Bay, Saskatchewan, Canada • 8-Bosumtwi, Ghana • 9-Gosses Bluff, Northern Territory, Australia • 10-Kara-Kul, Tajikistan 4 3 6 5 7 8 9 10

8. Do we see craters within our solar system? • Other solid bodies of our solar system also display round craters. We especially see these craters on the large ice-covered moons of Jupiter. Those moons display "palimpsest" craters which are merely surface markings because as time passed, the walls which originally existed sagged back onto the flat surface. • http://www.solarviews.com/cap/jup/eurgal2.htm • http://www.solarviews.com/cap/jup/callist1.htm

9. Why doesn’t the moon crash into the Earth? • http://www.chaosscience.org.uk/pub/public_html//article.php?story=20040629175315124 • Ok-if the moon is a great big enormous lump of rock, and it is up in the sky, why doesn't it fall down? • There was a very clever man about 400 years ago named Sir Isaac Newton who was thinking about this sort of problem. The first question he asked was “What do we mean by fall down?” If falling down means that everything falls in the same direction, and the world is round, things on the bottom of the Earth wouldn't stay there very long. So obviously falling down means something a bit different! What happens is that everything falls towards the center of the earth. Isaac started thinking about a cannon: he knew that the faster you fired a cannon ball, the further it went. • Next Isaac thought “What would happen if we had a really big cannon?” A really, really, really, reeeeaaally big cannon, and put it on top of a mountain-how far could you get it to go? • If you can make the cannonball go fast enough it keeps falling all the time but it never falls quite fast enough to actually hit the ground. This is called an orbit, and it is how astronauts, satellites, and the moon don't crash into the earth. • So the moon is actually falling down all the time, it just always misses the earth and always will. • Check out the flash activities on web page given at top!!!

10. Why do we sometimes only see slices of the moon? • http://images.google.ch/imgres?imgurl=http://aa.usno.navy.mil/graphics/Moon_phases_small.jpg&imgrefurl=http://aa.usno.navy.mil/faq/docs/moon_phases.html&h=473&w=315&sz=14&tbnid=HIqdmO0Z33WwfM:&tbnh=126&tbnw=83&prev=/images%3Fq%3Dphases%2Bof%2Bthe%2Bmoon&start=3&sa=X&oi=images&ct=image&cd=3 • From any location on the Earth, the Moon appears to be a circular disk which, at any specific time, is illuminated to some degree by direct sunlight. Like the Earth, the Moon is a sphere which is always half illuminated by the Sun, but as the Moon orbits the Earth we get to see more or less of the illuminated half. During each lunar orbit (a lunar month), we see the Moon's appearance change from not illuminated through partially illuminated to fully illuminated, then back through partially illuminated to not illuminated again. Although this cycle is a continuous process, there are eight distinct, traditionally recognized stages, called phases. The phases designate both the degree to which the Moon is illuminated and the geometric appearance of the illuminated part.

11. New Moon - The Moon's unilluminated side is facing the Earth. The Moon is not visible (except during a solar eclipse). Waxing Crescent - The Moon appears to be partly but less than one-half illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is increasing. First Quarter - One-half of the Moon appears to be illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is increasing. Waxing Gibbous - The Moon appears to be more than one-half but not fully illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is increasing.

12. Full Moon - The Moon's illuminated side is facing the Earth. The Moon appears to be completely illuminated by direct sunlight. Waning Gibbous - The Moon appears to be more than one-half but not fully illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is decreasing. Last Quarter - One-half of the Moon appears to be illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is decreasing. Waning Crescent - The Moon appears to be partly but less than one-half illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is decreasing. Following waning crescent is the New Moon, beginning a repetition of the complete phase cycle of 29.5 days average duration.

13. Do we always see the same side of the moon? • http://starryskies.com/The_sky/events/lunar-2003/eclipse9.html • Relative to the Earth, the Moon makes one rotation every 29.5 days. That happens to also be the time it takes for the Moon to complete one revolution around the Earth. This might seem like a coincidence, but it's not. • In the past, the Moon used to rotate much faster than it does now. But over millions of years, the effect of the Earth's gravity has slowed down the Moon's rotation until it became gravitationally locked to the Earth. This is why we always see the same side of the Moon. • It would seem logical to say that at any one time we can see 50% of the Moon's face. If the Moon were flat, that would be correct, but we know the Moon is a sphere. And the spherical shape of the Moon hides the area close to the perimeter and we can, at any one time, actually see only 41% of the Moon's face. • Even though the same side of the Moon's faces us, we do see a bit more than half of the Moon's face. Over time, because of “librations” we can see up to a total of 59% of the Moon's surface. • “Librations” are irregular motions of the Moon in its elliptical orbit around the Earth.

14. Why can we sometimes see the moon during the day? • http://content.scholastic.com/browse/article.jsp?id=4850 • The reason that you don't see the stars during the day is that the sky is too bright. But if you had a telescope and pointed it at a bright star you could still see it during the day! The stars are still there, just hard to see. The moon is bright enough that we can see it during the day or night. It orbits Earth once every 29.5 days. So during some of that time, it is easiest to see during the day and sometimes during the night. • http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970314b2.html • It might be useful to think of the sun as a large light bulb, and the moon as a large mirror. There are situations where we can't see the light bulb, but we can see the light from the bulb reflected in the mirror. This is the situation when the moon is out at night. We can't see the sun directly because the earth is blocking our view of it, but we can see its light reflected from the moon. However, there are also situations where we can see both the light bulb and the mirror, and this is what is happening when we see the moon during the day. You can explore this for yourself with a light and a hand mirror. Depending on which way you face (away from the light or sideways to the light) you can see either just the mirror, or both the light and the mirror.

15. What would happen to the Earth if the moon were gone? http://www.exitmundi.nl/moon.htm Well, not too many people know this, but the moon is what keeps our planet stable. Without it, we would find ourselves on a hostile rollercoaster world. Our planet would go berserk. For one thing, the moon tugs at the oceans. This gives us the tides. No moon, and the floods would immediately be about 2,5 times lower -- some minor tidal motion would remain, because the Sun pulls at the oceans, too. The consequences would be dramatic. Some areas would dry up, while others would become inundated with water. There would be all kinds of changes to nature. All over the world, people would face droughts, famines, diseases and wars. And to cheer you up a little more: that’s not the worst part.

16. Crucially, the moon also stabilizes the axis around which the Earth rotates. You could compare the Earth-moon system to an athlete swinging a hammer around. Take a good look at the picture on the right. Now, ask yourself: what would happen if the rope suddenly snapped? You get the idea: the athlete would fall over. Exactly the same thing would happen to the Earth if you took away the moon. Right now, our planet rotates at an axis that is tilted about 23 degrees. It has always roughly been that way. But without the moon, the Earth’s rotational axis would slowly drift off, because of the pull of the other planets -- especially Venus and Jupiter. So…one moment you’re in Africa; the next, you’re on the North Pole! Swing It Out: The moon and the Earth are locked into a twin system, much like an athlete about to hurl a hammer.

17. In the long run, this would cause massive, unpredictable and abrupt climate shifts. The Earth would heat up, freeze up, and heat up again. One moment, your nose freezes off in a massive Ice Age. The next moment, you find yourself sweating your eyeballs out, in a period of soaring heat. Even worse, our planet could tip over and ‘lie on its back’ for some millions of years (or longer). One half of the globe would be in constant sunlight, while the other half would be plunged into everlasting darkness -- and in cold.We’d have a two-sided planet. And to be honest, you probably don’t want to live on either side. The southern half would become a barren, waterless, roasted desert world. The northern half would be an equally barren, dry, ultra cold ice world. So…where do you go and where do you live?

18. Ok, so you let’s say you decide to live in between the sunny and the icy side. There, you might find a small zone with good old days and nights, and mild temperatures. But there’s a downside: the region will be harassed by HUGE, everlasting storms. With temperature differences like that, there would be massive flows of air between north and south.  And actually, that’s not even the biggest concern. Chances are the massive, abrupt climate shifts will at some point kill our world altogether. With the moon gone, our world could become a lifeless, dead planet in the end. The sweeping climate shifts could at some point disrupt the Earth’s atmosphere for good. This is probably what happened to Mars (once watery and friendly, but now as dead as a doornail). Mars indeed tilts like a drunken athlete: it tips over to about 60 degrees!  And that’s not everything. When the moon gets smashed up or knocked off course by a super big asteroid, it’ll probably rain debris on Earth for many years. For years, we’d have to wear hard hats - only to find that hard hats don’t help against big, incoming chunks of moon rock falling down on our world.

19. What are lunar eclipses? • http://science.nasa.gov/headlines/y2003/04nov_lunareclipse2.htm • Step outside on a sunny day, look down and examine your shadow. It's dark in the middle, pale and fuzzy around the edges, and it always points away from the sun. • Although we seldom see it, Earth has a shadow, too, much like your own: dark inside, pale outside, pointing away from the sun. Far away. Earth's shadow stretches almost a million miles into space, far enough to reach the moon. A lunar eclipse is when the moon passes into the Earth’s shadow. • The totally eclipsed moon won't be totally dark--and that's what makes totality delightful. Earth's atmosphere bends sunlight into our planet's shadow and onto the moon. This sunlight is reddened as it travels a great distance through our dusty atmosphere, and so the moon looks red. Sunsets on Earth look red for the same reason.

20. The Planets Stacy McCormack HST2006 “Discovering the Universe by Looking at the Sky”

21. Questions about the Planets • Why do the planets move around the sun? • What keeps the planets from crashing into each other? • What are some of the interesting points about each planet? • Is it summer when we are closer to the sun? • Is Pluto really a planet?

22. Why do the planets move around the sun? First of all, saying the planets go around the Sun is just another way of saying the planets are in orbit around the Sun. A planet orbiting the Sun is like the moon or a NASA satellite orbiting Earth. Now why does a planet orbit the Sun and not the Sun orbit the planet? The lighter object orbits the heavier one, and the Sun is, by far, the heaviest object in the solar system. The Sun is 1000 times heavier than the largest planet, Jupiter (which also happens to be my favorite planet), and it is more than 300,000 times heavier than Earth (another planet I am very fond of). In the same way, the moon and satellites we launch orbit Earth because they are so much lighter than our planet.

23. Isaac Newton realized that the reason the planets orbit the Sun is related to why objects fall to Earth when we drop them. The Sun's gravity pulls on the planets, just as Earth's gravity pulls down anything that is not held up by some other force and keeps you and me on the ground. Heavier objects (really, more massive ones) produce a bigger pull than lighter ones, so as the heavyweight in our solar system, the Sun exerts the strongest pull. Now if the Sun is pulling the planets, why don't they just fall in and burn up? Well, in addition to falling toward the Sun, the planets are moving sideways. This is the same as if you have a weight on the end of a string. If you swing it around, you are constantly pulling it toward your hand, just as the gravity of the Sun pulls the planet in, but the motion sideways keeps the ball swinging around. Without that sideways motion, it would fall to the center; and without the pull toward the center, it would go flying off in a straight line, which is, of course, exactly what happens if you let go of the string. http://spaceplace.nasa.gov/en/kids/phonedrmarc/2002_july.shtml

24. What keeps the planets from crashing into each other? The planets seem to be on a circular path around the sun, but they are not. Their path's are described as ellipses. An ellipse can be described as a stretched circle with two center points. The Sun is always at one of the center points in a orbit's path. Since the Sun is at one center point, when a planet nears that focal point it travels faster. As it goes further away from the Sun, the planet travels slower. The reason for this change in  velocity has to due with the Sun's gravitational pull. Now all planetary ellipses are not the same. Some are more curved than others, and some are longer than others. Scientists use eccentricity to describe each planet's orbital path shape.

25. All planets in our solar system move around the sun at their own speeds. They each move at different speeds because the Sun's gravity affects each planet at different distances. As mentioned before, when the a planet is closer to the Sun it travels faster than when it is further away. The closer to the Sun the stronger the gravity becomes resulting in more speed an object needs to escape its gravity. However, the planets work in a way that they don't have enough speed to escape the Sun's gravity, but enough not to be pulled in by the Sun's gravity. This state of equilibrium is what keeps the planets in orbit around the Sun. Is there a possibility that planets will crash into each other? The answer is no. Our solar system was designed to be stable. There are many forces (such as gravity and velocity) that are acting on the planets to keep them stable. The planets move at their own pace and in their own paths. The only two planets that do cross paths are Neptune and Pluto and they have no chance of meeting. http://library.thinkquest.org/C001245/OrbitPc.html

26. What are some of the interesting points about each planet? Mercury -Due to Mercury's rotation and highly elliptical orbit, the Sun appears to rise briefly, set, and rise again before it travels westward across the sky. At sunset, the Sun appears to set, rise again briefly, and then set again. The surface temperature on the side of Mercury closest to the Sun reaches 427 degrees Celsius, a temperature hot enough to melt tin. On the side facing away from the Sun, or the night side, the temperature drops to -183 degrees Celsius. http://starchild.gsfc.nasa.gov/docs/StarChild/solar_system_level2/planets.html

27. Venus - The daytime temperature is so hot it could melt lead (484 degrees Celsius). The dense atmosphere is composed of carbon dioxide and sulfuric acid which acts as a greenhouse and traps the heat. Earth - Earth is the only inner planet in our solar system that has liquid water on its surface. Seventy percent of the surface is covered by oceans where photosynthesis takes place. This makes the ocean the principal life habitat on Earth.

28. Mars - The Martian atmosphere is composed of over 95% carbon dioxide. At the Martian poles are polar ice caps which shrink in size during the Martian spring and summer. From data gathered by the Viking 1 and 2 probes, we know that the Martian surface is covered by various rocks and a soil which is rich in an iron-laden clay. The presence of iron explains the planet's reddish-orange appearance.

29. Jupiter - Jupiter is so large that all of the other planets in the solar system could fit inside of it! Clouds in the atmosphere move in alternating bands from east to west or west to east. Lightning, more powerful than any that has been experienced on Earth, has been noted in Jupiter's atmosphere. Also in Jupiter's atmosphere are oval features which are thought to be circular winds. The most prominent of these is the Great Red Spot, a hurricane-like storm that has been seen in Jupiter's southern hemisphere since Jupiter was first discovered. Jupiter has at least thirty-eight natural satellites.

30. Saturn - Saturn has the lowest density of any planet in our solar system. Its density is so low that it would float if it was placed in water! Saturn has an extensive ring system which is formed by a thousand individual rings. The rings appear to contain water ice and dust. The thickness of the rings ranges from 10 to 100 meters and the rings vary in brightness. There are gapsbetween some rings, while other rings appear to be braided together. Astronomers believe the rings developed from particles that resulted from the break-up of naturally occurring satellites.

31. Uranus - Uranus is unique in our solar system because it is tilted 98 degrees. When viewed from Earth, it appears to rotate on its side! At different times throughout its orbit, we can actually view one of the planet's poles head-on. This planet has a system of rings which was not discovered until 1977. The ring system contains eleven dark rings composed of varying sized particles. Satellites embedded in the rings create gaps between the rings. Uranus has 21 known natural satellites (and may have at least 27), both within the rings and outside of the rings.

32. Neptune - Neptune has a mantle of liquid hydrogen while the atmosphere is a combination of ammonia, helium, and methane. In the upper atmosphere, methane freezes and forms an ice cloud which casts a shadow on the clouds below. Neptune has bands in its atmosphere where wind speeds may reach 2000 kilometers per hour! It also has a ring system consisting of four rings; two thin and two thick. The rings are composed of dark particles which vary in size. Neptune has at least eight natural satellites, four of which orbit within the rings.

33. Pluto - Pluto has more in common with Triton, Neptune's largest moon, than it does with any of the other eight planets in our solar system. Pluto is actually smaller than Triton. Pluto has one natural satellite, Charon, which is half the size of Pluto. Because Pluto and Charon are comparable in size, many scientists consider them to be a double planet. Studies have detected methane frost on Pluto and water frost on Charon. Like Triton, Neptune's satellite, Pluto has an atmosphere of nitrogen and methane. Pluto's atmosphere appears to extend out to include Charon, which suggests that they may share an atmosphere. Through the Hubble Space Telescope, Charon appears to be more blue in color than Pluto. During the time in its orbit when Pluto is farthest from the Sun, its atmosphere condenses and falls to the surface as frost.

34. Is it summer when we are closer to the sun? • http://www.scienceu.com/observatory/articles/seasons/seasons.html The Sun is our main source of heat, and since these changes are the same every year, it surely has something to do with the movement of the Earth around the Sun. If we get closer to a fire, we get hotter. Could it be then that the Earth gets closer to the Sun during Summer, and farther during Winter? This idea seems at first to have some merit, until we remember that the seasons get reversed when we cross the equator: when it is Summer in the northern hemisphere, it is Winter in the southern one, and vice versa. And surely Argentina is at the same distance from the Sun as the USA! Besides that, the Earth's orbit is an ellipse, not a circle, so at some times the Earth is closer to the Sun than at others; but this ellipse is very nearly a circle, and the relatively small differences in distance to the Sun cannot account for the changes in temperature. And to make things worse, the Earth is actually closer to the Sun during the northern hemisphere Winter!

35. What causes this? The Earth rotates around an imaginary line passing through the poles, called the axis. This line forms an angle (called the tilt) of 23.4° with the perpendicular to the orbit of the Earth around the Sun. As the Earth moves around the Sun, this axis stays always pointing in the same direction. This means that during part of the year the northern part of the Earth will lean more directly against the sun and during other parts the southern part will. What has this to do with temperature? Well, when the northern hemisphere is leaning away from the sun, the rays coming from it hit this part of the Earth at a smaller angle than on other parts of the world. This means that the same amount of light is distributed over a larger surface, and therefore these places receive less heat than the others. The southern hemisphere is experiencing Summer, the northern hemisphere Winter. In half a year, the situation reverses, and it is now Winter in the southern hemisphere since that part of the earth is now leaning away from the sun. The seasons are then the result of this tilt of the Earth's axis. If the tilt of the Earth's axis was 0° there would be no difference in how the rays from the sun hit its different regions, and there would be no seasons.

36. Is Pluto really a planet? http://science.nasa.gov/newhome/headlines/ast17feb99_1.htm Pluto is 6 times smaller than Earth, and even smaller than seven of the solar system's moons (the Moon, Io, Europa, Ganymede, Callisto, Titan and Triton). Pluto's own moon, Charon, is larger in proportion to its planet than any other satellite in the solar system. Some astronomers consider the pair to be a double planet. Pluto's elliptical orbit is also unusual. It is the only planetary orbit which crosses that of another planet (Neptune), and it is tilted 17 degrees with respect to the plane of the solar system. Astronomers once thought that Pluto may have been a satellite of Neptune's that was ejected to follow a tilted elliptical path around the sun. However, careful simulations of the orbits and dynamics of Pluto and Neptune indicate that this is an unlikely scenario. Pluto's composition is unknown, but its density (about 2 gm/cm3) indicates that it is probably a mixture of rock and ice. All the other rocky planets -- Mercury, Venus, Earth and Mars -- are located in the inner solar system, close to the Sun. Except for Pluto, all of the outer planets -- Jupiter, Saturn, Uranus and Neptune -- are gaseous giants. Once again, Pluto is a misfit.

37. Despite its well-known peculiarities, Pluto's official status as a planet was never in jeopardy until 1992 when David Jewitt and J. Luu discovered a curious object called 1992 QB1. QB1 is a small icy body, similar in size to an asteroid, orbiting 1.5 times further from the sun than Neptune. QB1 was the first hint that there might be more than just Pluto in the distant reaches of the solar system. Since then nearly 100 objects like QB1 have been found. This swarm of Pluto-like objects beyond Neptune is known as the Kuiper Belt. Astronomers estimate that there are at least 35,000 Kuiper Belt objects greater than 100 km in diameter, which is several hundred times the number (and mass) of similar sized objects in the main asteroid belt. So, is Pluto really a planet or is it more like a dormant comet, simply the largest known member of the Kuiper Belt? That's the question that astronomers have recently been debating. Other than its relatively large size, Pluto is practically indistinguishable from the Kuiper Belt objects (KBOs) and short period comets. David Jewitt and his colleagues at the Institute for Astronomy are leaders in the search for new members of the Kuiper Belt. They have discovered over 40 KBO's in recent years, some of which are comparable in size to Pluto. "We've already found objects 1/3rd the diameter of Pluto," says David Jewitt," even though we have examined only a tiny fraction of the sky. An example is 1996 TO66, which is 800 km diameter. It would be incredible in its own right if Pluto proved to be the only 2000 km object. I think we'll have Pluto II, Pluto III....within a few years."

38. Dr. Jewitt raises the interesting possibility that Kuiper Belt objects might one day be discovered that are even larger than our ninth planet. If that happens, what does it mean for Pluto? Should it be stripped of planetary status and reclassified as a member of the Kuiper Belt? Or should newly discovered "Plutos" be classified as planets as well? These are difficult questions that await the astronomical community. For now, however, Pluto's status as a planet seems secure. In a press release dated Feb. 3, 1999 the International Astronomical Union stated that "No proposal to change the status of Pluto as the ninth planet in the solar system has been made by any Division, Commission or Working Group of the IAU responsible for solar system science. Lately, a substantial number of smaller objects have been discovered in the outer solar system, beyond Neptune, with orbits and possibly other properties similar to those of Pluto. It has been proposed to assign Pluto a number in a technical catalogue or list of such Trans-Neptunian Objects (TNOs) so that observations and computations concerning these objects can be conveniently collated. This process was explicitly designed to not change Pluto's status as a planet."