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p226 1. The distance to the moon is most accurately measured by laserranging; using reflectors placed on the moon during the Apollo program to reflect laser beams fired from earth. 2. Mercury is seldom seen with the naked eye because it is so close to sun that is usually hidden in the sun’s glare. 3. Early astronomers probably thought Mercury was two planets because of the speed with which it appeared on either side of the sun. 4. The average molecular speed of atmospheric gases exceeds the escape speed of both the moon and Mercury, thus neither can hold an atmosphere. 5. Lunar maria appear smoother, flatter and darker than surrounding lunar highlands, and from a great distance bear a resemblance to bodies of water. 6. Mercury and the moon look very similar, they each are small & have essentially no atmosphere. Differences: Mercury has warmer sun side than the moon, it doesn’t appear to have maria-like features, and it does have scarps. 7. Synchronous orbit means moon rotates once per orbit; Earth’s gravity deformed the moon slightly, and continues pulling on that deformity. The moon is said to be “tidally locked” to the earth (as are most moons in the solar system). 8. 3:2 orbit spin resonance means Mercury rotates two full times during every three orbits; Mercury could not establish a synchronous orbit (as the moon did) because Mercury’s orbit is too elliptical. 9. A scarp is a “wrinkle” (but if you were there it would look like a cliff!) in the surface of Mercury, caused when the planet’s warm surface cooled and shrank. Scarps cut across craters, which means scarps formed AFTER the craters had formed. 10. Meteorite impacts are the only real sources of “erosion” on the moon; with no atmosphere or running water most surface features are there forever unless disturbed by an asteroid impact. 11. As of the publication date of this book, ice evidence is circumstantial: Lunar Prospector detected large amounts of hydrogen at the lunar poles in 1998. Today we have found craters that reflect light in dramatically different way than other craters do. Also, when we have crashed satellites onto craters and the impact plumes: ice is apparent. 12. The maria have FAR fewer craters, and these craters generally are smaller than those in the highlands. Since large craters are rare, for the highlands to have many of them indicates great age. 13. The moon and Mercury have no atmosphere to moderate daily temperature ranges the way earth does. (Earth ranges from 180 K to about 330 K = -90˚C to 60˚C) 14. Both moon & Mercury have been geologically dead for several billion years. The moon has a small iron core while mercury’s core is believed to be mostly iron. 15. The impact theory of Moon Origin is currently in vogue among astronomers and astrogeologists: A Mars-sized object collided with earth when earth was young; the material that was torn loose from the impact (literally) gravitated back together to form the moon. 16. The moon orbits the earth so lunar observers would see the earth go through phases; crescent, quarter, gibbous, full and new. 17. The best part of the moon to observe with a telescope or binoculars is the terminator line. The long shadows in this area highlight the varied texture of the moon’s craters, maria and highlands. If you were standing on the moon’s terminator (or the terminator of ANY body, by definition) the sun would appear on the horizon. On earth, you are on the terminator twice daily, at dawn and at dusk. 18. Were I to establish an observatory on the moon, I would want the least solar glare, so I would chose the bottom of a polar crater, where the sun never reaches. Any other location would have the sun in the sky for 14 earth days at a time, but of course the bottom of a polar crater on the moon is one of the coldest places in the entire solar system! 19. At midnight in the night sky, the sun is under your feet, on the other side of the earth! Mercury never gets more than 28˚ away from the sun (a bit more than pinky-tip to thumb-tip on a fully spread hand), so there’s no way you could ever see it high overhead in the night sky. 20. The lava that came to the surface to form the smooth maria did so on the near side because the crust on the near side was much thinner.