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Faces of the Moon

Last week we discussed our mission’s starting point and one of our biggest challenges; getting off the surface of our planet. This phase of the mission is accomplished by using large powerful rockets to ‘blast off’ the Earth. We also discussed the Scientific Method and how we use it to help us answer important questions and find solutions to our challenges through experimentation. This week we will look at our journey’s end – our Moon. A Turbulent History for the surFACE of the Moon Although there are several theories, the exact origin of the Moon remains a mystery. Lunar rocks and meteorites reveal the Moon, Earth, and probably the rest of the planets in our solar system were formed about 4.5 billion years ago. Scientists believe (hypothesize) that its surface was once covered with a molten magma ocean several hundred miles deep, and it was once much closer to the Earth than it is today. In fact, the Moon is steadily moving farther away from the Earth at a rate of about 1.5 inches per year. The Moon’s terrain is ‘scarred’ with many thousands of large, medium and small holes called ‘craters’. These craters were caused by meteorites impacting the surface of the Moon. The ‘cratering’ rate billions of years ago was about one thousand times the current rate. Occasional large impacts, involving meteorites a few kilometers wide, created major craters, throwing out bright rays of pulverized debris across the surface. Smaller meteorite impacts churned the upper soils, producing its basaltic dust (called regolith) and rock surface. Ancient observers of the Moon believed that the dark features on its surface were oceans, giving way to the name ‘Maria’, which is Latin for ‘Seas’. The Maria formed when molten rock erupted onto the surface and solidified a few billion years ago. It is also believed that Comet impacts have deposited water on the Moon and that water exists in the form of ice in the very dark and cold areas at the poles. In fact, NASA’s recent missions to the Moon (Lunar Reconnaissance Orbiter “LRO” and LCROSS) have reported finding water ice at the poles. Many of the lunar lander missions also conducted scientific experiments to help scientists determine the origin of the Moon. Moreover, the Apollo astronauts brought back lunar rocks to help determine the geological and chemical composition of the lunar soil. We will use all the data and information learned from our historic exploration of the lunar surface to help design our mission. Here is a short video about how NASA is counting the craters on the Moon to help learn about the early history of our solar system: How many craters do you think there are on the surface of the Moon? Let’s now look at another example of using the Scientific Method we learned last week to help us answer more questions. Here is an experiment that you can perform at home (with adult supervision, of course) to help you better understand how large, medium and small craters are formed on the Moon: We have now learned a little bit about the lunar terrain that we will have to travel across to win the GLXP. There are many craters and rocks to avoid or it’s going to be a very bumpy ride. We will have to take this into consideration as we design our rovers. Face of the Moon We see the same face of the Moon (the ‘near side’) all the time because the Moon rotates once on its axis in very nearly the same time that it takes to travel once around the Earth. Although we cannot see the ‘far side’ of the moon, the side of the Moon that faces away from the Earth, it is half the time in light and half in darkness, just like how it is on Earth. Therefore, there really is no actual ‘dark side’ of the Moon. The Moon shows us its different ‘phases’ as it moves along its elliptical (or eccentric) orbit around the Earth at an average speed of ~3,700 km/hr (~ 2300 mph). It takes about 29.5 days for the Moon to go from one phase to the next same phase. During this period of time the Moon completes 8 major phases which is known as a lunar month. The phases of the Moon depend on how much of the sunlit surface can be seen at any one time (we will learn about these phases next in the blog). Let’s look at a few of the basic properties of the Moon relative the Earth: • Distance from Earth = ~238,857 miles (384,403 km) • Diameter = ~2,163 miles (3,480 km) (~ 27% of Earth) • Mass = 7.36 x 10^22 kg (~1.2% that of Earth) • Gravitational Acceleration = ~1/6 that of Earth • Orbital Period (1 orbit around the Earth) = 27.3 days • Temperature Range = ~225˚F to -245˚F Wow, that temperature range is really extreme. So, we are going to have to make sure that our rovers can survive in both the 'really hot' sunlight and 'really cold' darkness. ‘Phaces’ of the Moon Each lunar month our Moon passes through several different stages. Although this cycle is a continuous process, there are eight distinct, traditionally recognized stages, called phases. These phases are named after how much of the Moon we can see and whether the amount visible is increasing or decreasing each day. The phases designate both the degree to which the Moon is illuminated (sunlit) and the geometric appearance of the illuminated part. These phases of the Moon, in the sequence of their occurrence (starting from New Moon), are described below. As mentioned above, it takes our Moon about 29.5 days to completely cycle through all 8 phases. Occasionally (about 2.8 years), there are two Full moons in the same month. This is referred to as a ‘Blue Moon’. Hence, the origin of the saying “once in a Blue Moon” used colloquially to mean "a rare event". Here is the description of each of the 8 Phases of the Moon: 1. New Moon: In this phase the Moon is roughly in the same direction as the Sun, its illuminated half is facing away from the Earth, and therefore the part that faces us is dark because the side of the moon facing the Earth is not illuminated. Additionally, the Moon and the Sun rise and set at about the same time. Consequently, the moon is up throughout the day, and down throughout the night. For these reasons we cannot see the moon during this phase. 2. Waxing Crescent: As the Moon moves around the Earth, we get to see more and more of the illuminated half, and we say the Moon is "waxing" because each night a little bit more is visible for a little bit longer. At first we get a sliver of it, which grows as days go by. This lunar sliver can be seen each evening a few minutes just after sunset. 3. First Quarter: A week after the New Moon, when the Moon has completed about a quarter of its turn around the Earth, we can see half of the illuminated part; that is, a quarter of the Moon. During first quarter, 1/2 of the moon’s disk is visible for the first half of the evening, and then goes down, leaving the sky very dark. This is why it is also referred to as a Half Moon. 4. Waxing Gibbous: During the next week, we keep seeing more and more of the illuminated part of the Moon, and it is now called Waxing Gibbous (gibbous means "humped or bulging"). When most of the Moon is visible, more than half but less than fully illuminated, we say it is a Gibbous Moon. Observers can see all but a little sliver of the moon. During this phase, the Moon remains in the sky most of the night. 5. Full Moon: Two weeks after the New Moon, the moon is now halfway through its revolution, and now the illuminated half coincides with the one facing the Earth, so that we can see a full disk. When we can observe the entire face of the moon, we call it a Full Moon. At this time the Moon rises at the time the Sun sets, and it sets when the Sun rises. If the Moon happens to align exactly with the Earth and Sun, then we get a lunar eclipse. 6. Waning Gibbous: From this point on, until it becomes new again, the illuminated part of the Moon that we can see decreases, and we say it’s “waning”. The first week after the Full Moon, is called Waning Gibbous. Like the Waxing Gibbous Moon, during this phase we can see all but a sliver of the Moon. The difference is that instead of seeing more of the Moon each night, we begin to see less and less of the Moon each night. This is what the word "waning" means. 7. Last Quarter: Three weeks after the New Moon, we again can see half of the illuminated part which is called Last Quarter. During a Last Quarter Moon we can see exactly 1/2 of the Moon's sunlit surface just like the First Quarter Moon. 8. Waning Crescent: Finally, during the fourth week, observers on Earth can only see a small sliver of the Moon, and only just before morning. We call this a Waning Crescent Moon because each night less of the Moon is visible for less time. A short while after four weeks (29.5 days, more precisely) the illuminated half of the Moon again faces away from us, and we come back to the beginning of the cycle: a New Moon. Here is a short video explaining the geometry of the 8 Phases of the Moon: As with the other properties of the Moon we discussed above (terrain, temperature, etc.), we will also have to plan our mission taking into consideration the different phases of the Moon; that is the time that our rovers are in sunlight or darkness. Finally, here is a catchy tune to help you remember the Phases of the Moon: Hope you enjoyed the blog, Mystical Moon
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