Untitled Document-2 PDF - Astronomy Notes

LEC 4 The Moon → earth blocks the sun, lunar eclipse → moon blocks the sun, solar eclipse → the orbit of the moon is tipped 5 deg, which is why lunar ec- happens → New Moon a really thin crescent when the moon is in the direction of the sun the only time a solar eclipse ca...

LEC 4 The Moon → earth blocks the sun, lunar eclipse → moon blocks the sun, solar eclipse → the orbit of the moon is tipped 5 deg, which is why lunar ec- happens → New Moon a really thin crescent when the moon is in the direction of the sun the only time a solar eclipse can happen unlit side faces the earth rises with the sun and sets with the sun not generally visible → Waxing Crescent 3-4 days after the new moon rises around 3 hrs after the sun sets around 3 hrs after the sun easiest to see right after sunset → Waxing quarter 1 week after the new moon moon is lit from the side rises around 6 hrs after the sun sets around 6 hrs after the sun easiest to see night before midnight → Waxing Gibbous 10-11 days after the new moon kisses around 9 hrs after the new moon sets 9 hrs after the sun → Full Moon two weeks after the new moon the only time lunar eclipse can happen rises 12 hrs after the sun rises sets 12 hrs after the sun sets  visible most of the night → Waning Gibbous 10-11 days before the next new moon rises around 3 hrs before the sun rises sets around 3 hrs after the sun sets → Waning Quarter a week before the next new moon rises 6hrs before the sun rise sets around 6hrs after sun sets Rises around midnight, and is up the rest of the night and morning → Waning Cecsent 2-4 days before the next new moon Rises 3 hrs before sun rises Sets 3 hrs after sun sets Easiest to see before sunrise → Solar Eclipse when the moon blocks light from the sun happens when the new moon crosses the ecliptic plane bc the moons orbit is tipped relative to the ecliptic plane, this happens rarely it only casts a shadow on the small part of the earth → Lunar Eclipse When the moon enters the Earth’s shadow happens when a full moon crosses the ecliptic plane can be seen from anywhere on earth more common that a solar eclipse (The earth is larger than the moon, so has a larger shadow) → Problem with my model / simulation size of the sun and the orbits are very much not to scale The tilt of the moons orbital plane is wrong The moons rotation axis should be tipped a little to orbital axis the orbit should be perturbed ellipses, not circles the position of the sun and the earth should be effected by everything else on the solar system orbits should not be centred on the sun and on the earth  orbits should change speed, depending on distance from the object being orbited the orbital plane of the moon should precess around every 18. years LEC 5 Astronomy before Copernicus → observations sun, moon, and stars rise and set everyday the earth feels fixed the stars don't seem to change everything falls to earth The planets experience “retrograde motions” → Conclusion the earth is the centre of the universe everything revolves in circles around it the planets move in circles within circles → assumptions the heavens are perfect and incorruptible ‘circles are perfect The Geocentric Universe In this model: → the earth is the centre if the universe → The celestial objects revolve around earth A different idea → Nicolaus Copernicus catholic/ canon scholar he was also a diplomat Economist translator → a different idea  the sun is the centre of the universe planets orbit the sun in circles the moon orbits the earth Apparent Retrograde motion → earth orbits faster than mars → as earth passes mars, the position of mars on the sky, compared to background stars, changed → this can explain the motion of the planets on the sky Tycho Brahe (1546-1601) danish nobleman had his own island and observatory was exiled over politics Made extremely precise measurements of the motion of mars observed a super nova used parallax to constrain distance from his data current models clearly had problems Johannes Kepler 1571-1630 worked from Tyco brakes data was concerned with the inaccuracy of the current models for the theological reasons discovers a fix for Copernicus model → Keplers first law: (the orbit of each planet about the sun is an eclipse with the sun at one focus) → Keplers second law: (A planet moves faster in the part of its orbit nearer the sun and slower when the further from the sun, sweeping out equal areas in equal times) → Keplers third law: (more distant planets orbit the sun at slower average speeds, obeying a precise mathematical relationships)