ASTRO SOLAR SYSTEM
ASTRO SOLAR SYSTEM ASTR 1010
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This 5 page Class Notes was uploaded by Bernie Pagac on Saturday September 12, 2015. The Class Notes belongs to ASTR 1010 at University of Georgia taught by Magnani in Fall. Since its upload, it has received 27 views. For similar materials see /class/202361/astr-1010-university-of-georgia in Astronomy at University of Georgia.
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Date Created: 09/12/15
Group 2 Jeremy Brandt Chris Bragg Sean Brunson Gabrielle Bolton Savannah Boyd Juliet Campbell M Broullire Chapter 1 and 2 Notes Motion The motion of bodies in the solar system is periodic and can be predicted Can be used to tell time seasons day Important to understand astrology vs astronomy 0 astro star logy study of o nomy system of laws governing a body of knowledge Astrology is NOT a science Astronomy is a science A revolution around Earth s axis day Lunar cycle month Earth around the Sunyear Newtonian Mechanicstheory of motion Galaxies 73 of the matter in the universeDARK ENERGY 23dark matter 4normal stuff Galaxy a bunch of stars a few hundred billion stars speed of light3x10quot8 meterssec Alpha Centauriclosest star besides the sun AC B Proxima closest one Week 2 Notes for 12312 Lunar Motion It takes around a month for the moon to go around the earth but there s a bit of a complication with that The reference point determines how long it takes for the moon to orbit A solar month is 295 days but a sidereal month is 273 days The earth moves around the sun at the same time that the moon is going around the earth By the time the moon gets lined up with a star again from one orbit to the next the moon has not gone around completely with respect to the sun Sidereal Month is the time it takes the moon to return to the same alignment with a star It takes a little bit longer for a Solar Month because the earth has moved around the sun So a month is about 30 days to keep in line with the Solar Month The Moon keeps the same face pointed towards the earth 7 in other words it revolves on its axis in the same amount of time it takes to go around the earth So a lunar day a lunar year rotation revolution Something happened to the moon to force it to have such a strange rotation revolution ratio It is not a coincidence 7 it is a phenomenon known as TIDAL LOCKING a gravitational effect The moon spun faster in earlier times but the earth slowed it down over time so that the same face is now permanently pointing towards the earth So we ve never seen the dark side of the moon from earth But it is not always dark 7 we just can t see it when it s in light which is half the time It is more correct to call it the far side of the moon The geometry of the situation dictates the repetition of this pattern This repetitive pattern can be used to tell time The phase of the moon as well as its place in the sky can be used to tell time Lunar Motion Highlights Takes the moon around 30 days to circle the Earth o Solar month295 days 0 The sun doesn t line up like other stars because it isn t far away enough for it to have the effect of it converging in the distance Sidereal month 273 days 0 Stars as a reference o The moon always faces the moonwith the same side o Moon revolves in the same time it takes it to rotate around the earth o Tidal locking The moon spins around on its axis at the same rate as it takes it to go around the Earth o The Dark Side of the Moon though more accurately far side of the moon o can tell time by the location of the moon and its phase Eclipses are important when talking about the moon A LUNAR ECLIPSE is when the moon is covered by the earth s shadow Earth is between Moon and Sun A SOLAR ECLIPSE is when a bit of the earth is covered by the moon s shadow Moon is between Earth and Sun The earth s show easily covers the whole moon during a lunar eclipse But the moon is smaller than the earth so the moon s shadow doesn t block out the entire earth during a solar eclipse The full shadow of the moon is called the UMBRA which is totally dark because at this one point the moon totally covers the sun Surrounding the umbra is the PENUMBRA which is only a partial eclipse When the moon completely covers the sun you can see a CORONA around the edge of the moon and this is the only time when this is Visible During a total lunar eclipse the moon looks reddish Clearly a Lunar Eclipse covers a Full Moon For a Solar Eclipse you need a New Moon These happen this way because of the position of the moon during these times So why are there only 2 solar or lunar eclipses per year The problem is that the moon is tilted about 5 degrees from the Ecliptic Plane the plane of the earth sun orbit Most of the Full and New Moons occur either above or below the Ecliptic You only get total eclipses when the Full or New Moon crosses the Ecliptic The line of intersection of these 2 planes has to point towards the Sun This intersection is called the LINE OF NODES But the line precesses in 346 days a little less than a year which is why you don t get eclipses at exactly the same times each year Lunar Eclipse Highlights Lunar Eclipse When the moon is covered by the earth s shadow so the earth is between the moon and sun Has to be a full moon Solar Eclipse a bit of earth is covered by the moon s shadow The moon is between the earth and sun Only covers a small area on earth Umbra full shadow Penumbra partial shadow in a complete solar eclipse is the only time the corona can be Viewed Eclipses occur only a couple times a year because the moon sun and earth are not always on the same plane Notes for 12512 Predicting Eclipses Figure out the 2X per year when the Line of Nodes is pointing towards the sun The orbital plane of the moon precesses which makes it hard to determine The ECLIPSE YEAR is the precessional period of the orbital plane of the EarthMoon system which ends up being 3466 days With this knowledge we can predict eclipses With there being 2 eclipses per year you get one every 1733 days The lunar cycle is 295 days If you start with Day 0 you can figure out when these 2 sync up 7 it takes 183 years to get the same con guration This is called the SAROS CYCLE The Calendar Gregorian vs Iulian 7 based on the Roman model Romans and Babylonians used the First Point of Aries to mark the beginning of the year But it didn t work every year 7 after 4 years it took an extra day to get back to the point So the average approximation for the year is 36525 days One way to deal with this is the leap year but this was seldom done Some societies added an extra day or month called INTERCALATION The Romans changed their policy of monthly intercalation because it was politically controlled In other words they were non astronomical reasons for intercalation Because of this misapplication of the rules the Romans got off by about 3 months Julius Caesar in 46 BC standardized the calendar with an astronomer named Sosigenes of Alexandria Thus they added 3 extra months to the calendar bringing the vernal equinox back to March 25th and introduced the Leap Year so that it wouldn t be politically decided This is the advent of the Julian Calendar and it was used in the West for 15 centuries But the year is actually 365242199 days long It was a close estimate but not close enough over longer periods of time By the 16th century the vernal equinox had shifted to March 11th because of this discrepancy Pope Gregory III decided to drop 10 days and bring the vernal equinox back to March 21st But the calendar had to be tweaked 7 so he changed the leap year Every end of century 1600 2000 etc divisible by 400 is a leap year and only these end of century years are leap years It makes the average year 3652425 days which is much closer It will eventually get out of sync too but it will take much longer This is the Gregorian Calendar which we still use today England and the American colonies didn t use this system until 1752 And now to the Mayan Calendar They had 2 basic calendars 7 the divine almanac 260 days long for religions purposes and the solar calendar 365 days They also had a combination of these 2 which was called the Calendar Round system it had a pattern than repeats every 52 years But the one everybody s talking about is the Long Count It is a continual number of days for more than 5000 years Every day for 5200 years has a different name This system doesn t have to use leap years at all 7 it is a running count of days which makes it easy to determine how long ago something happened It begins counting in August of 3 1 14 BC When you run through all of the cycle with each date named it runs out on Dec 21st 2012 A new cycle begins the next day According to the Mayan calendar we are in the 5th such cycle so the 6th will begin on Dec 22nd 2012 Highlights Before the Julian Calendar there were many calendars then the Iulian gave way to the Gregorian Calendar The year is not exactly 365 days it is closer to 36525 so using the stars to chart things it gets off Intercalate adding an extra day or month Leap Year Adding one day every four years Iulian Caesar consulted an astronomer named Sosigenes ofAlexandria in 46 BC found a way to sync it back up and get rid of intercalate This brought the vernal equinox back to March 25 and introduced the leap year The year however is actually 365242199 days long Pope GregoryXlH decided to drop 10 days and bring the Vernal equinox to March 21st He also institute a tweak to the leap year system by saying every century that is divisible by 400 would be a leap year Mayans 2 basic calendars Divine Almanac 260 days Solar Calendar 365 days Two additions combination of Calendar Round System Long Count It had five boxes which helped create unique names for each day for millions of days Notes for 12712 The RETROGRADE motion of the outer planets Mars Jupiter Saturn is a problem in the GEOCENTRIC earth centered model of the solar system The inner planets Mercury and Venus always stayed near the sun 7 Venus was never above the horizon at sunset So a model has to account for all this Some of the ancients invented EPICYCLES 7 orbits on top of orbits 7 to account for the planetary motion Ptolemy in the 2nd century AD perfected this idea This was the main model until the 15th century despite its inability to predict the positions of the planets in the future Who solved the problem The Copernican Revolution in the 1450s brought a HELIOCENTRIC sun centered model Copernicus resurrected this model from the ancient Greek guy Aristarchus 2nd 3rd centuries BC But the Greeks couldn t measure parallax so they didn t have the evidence to support heliocentrism That s why they never believed this model The problem with Copernicus model is that he used perfect circles for orbits since people
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