Understanding Motions in the Sky: Earth, Moon, Sun, and Telescopes, Study notes of Astronomy

Download Understanding Motions in the Sky: Earth, Moon, Sun, and Telescopes and more Study notes Astronomy in PDF only on Docsity! 1 AST 1002 Planets, Stars and Galaxies Section 1 -- MW 3:35-4:50 pm; Section 2 -- MW 5:15-6:30 pm class website – has syllabus, schedule, etc. http://www.physics.fsu.edu/users/Lind/AST1002/default.htm Today’s Lecture: purpose & goals “Motions in the Sky1: Earth, Moon, & Sun” Review üUnderstand that the Moon Revolves Around the Earth -- leads to the phases of the Moon üUnderstand that the Earth and Moon cast shadows from the Sun -- leads to Eclipses üUnderstand that the Earth orbits the Sun in a tilted orbit -- leads to the Seasons Summary Prof. David Lind, FSU Physics telescope with large aperture telescope with small aperture telescope with medium aperture Ai Review: Three Powers of a Telescope n A telescope is a device to “see far as if near” n To “see far as if near” a telescope must have: the ability to detect very faint objects: n called Light-Gathering Power. n Dependent on the diameter of the telescope aperture – the bigger the better! n “light pollution” the ability to separate the images of two objects very close together: n called the Angular Resolution. n Dependent on the diameter of the telescope aperture – again the bigger the better! n “seeing” the ability to visibly expand the size of images: n called Magnification. n Dependent only on the curvature of the telescope optics (focal length). LGP2/LGP1 = A2/A1 = (D2/D1)2 α(arcsec) = 2.0x10-3 x λ(Å)/D(cm) M = fo/fe n Atoms and Starlight – n Astronomers are forced to be observers n we must extract as much information as possible from the starlight. n how light interacts with matter. n The star’s temperature n “blackbody” or Planck radiation is emitted by all warm objects n Wien’s law and the Stefan- Boltzmann law (next page) n The star’s composition n light interacts with the electron energy levels in atoms. n quantum model of atoms n The relative motion of the star and the observer n Doppler effect Review: Light – “the Starry Messenger” λ1→2 = E2 – E1 hc 2 Temperature and Radiation Examples: Wien’s Law: T(K) = 2,900,000/λmax(nm) T(K) = 2,900,000 /480 = 6040 2If one star has a surface temperature of 6000K, and a second star with the same surface area has a temperature of 2000K, how much brighter will the first star be? Stefan-Boltzmann Law: L = 4πR2 . σT4 use ratios to solve: 1If a star emits radiation most strongly at a wavelength of 480 nm, what is the surface temperature of that star? K L1/L2 = 4πR12 .σT14/ 4πR22 .σT24 = (R1/R2)2 . (T1/T2)4 = 1/12 . (6000/2000)4 = (3/1)4 = 81 Reminder – Classroom etiquette n Be prepared when you come to class: n Read the course material before coming to class n Have with you pencil, paper, calculator; there may be a quiz! n Turn off your cell-phone when you come into the classroom: n Simple courtesy! It’s disruptive of the lecture and the other student’s ability to learn. n I expect you here the full period of the class time: n Class starts at either 3:35pm or 5:15pm – please be in your seats by that time. n Class ends at either 4:50pm or 6:30pm – I expect the courtesy of you staying until I am finished with the lecture; I work very hard to finish a few minutes early so you have passing time to the next class, but will be happy to give pop-attendance quizzes every time someone is rude and leaves early. Preview – Motions in the Heavens n The Universe has many kinds of motion n The spinning of the Earth causes the rising and setting of the Sun and stars n The revolution of the Earth around the Sun determines the year n The tilt of the Earth determines the seasons n The spinning, revolution and tilt determine the part of the sky which is visible n You want/need to understand these motions n Today, we will focus first on the motions of the Earth, Moon, and Sun and see how they behave together. 5 Path of the Moon Definitions: Siderial Month (27.32 days) – “with respect ot the stars” Synodic Month (29.53 days) – “with respect to the Sun” (determines length of phases) § Interesting Note: The most massive object, and thus the one that all the other objects orbit around, is the Sun, not the Earth. “Dark Side” of the Moon n The Moon doesn’t have a “dark side” n Everywhere on the Moon, the Sun rises and sets once per month n It does have a side which always faces away from us n During a New Moon, this far side is the side completely illuminated Eclipses n Eclipses occur when the Sun, the Earth and the Moon all lie along a straight line n They must line up in all 3 dimensions + in time n If the Moon and Sun followed the same path around the Earth (the ecliptic), we would see eclipses every month, but the Moon’s orbit is tilted 5o to the ecliptic, so there are only two times a year when the paths overlap (“eclipse seasons”). 6 Shadows n Umbra n dark cone of complete shadow n Penumbra n lighter area of partial shadow Solar Eclipse n The Moon is between the Sun and the Earth (New Moon) n as seen from the Earth, the Moon blocks the Sun either partially (annular or partial eclipse) or fully (total eclipse) n A truly amazing sight (can see and study the sun’s atmosphere) Solar Eclipse (cont.) n The Sun and the Moon have the same apparent size in the sky (~½ o wide) à “small angle formula” n Sun is 400 times larger than the Moon, but 400 times farther away (ratio the same!!) n Earth to Moon distance varies (elliptical orbit) so sometimes the Moon won’t totally block the Sun n area of total eclipse is small n 0 to 175 km wide n time of total eclipse is short n 0 to 7 minutes n shadow moves across Earth at 1500 km/hr n partial eclipse is visible 3000 km on either side n Earth is the only place in the Solar System where solar eclipses occur like this. 7 Recent & Upcoming Solar Eclipses South Pacific, Mexico, Eastern USA4.5April 8, 2024 … Pacific Ocean, USA, Atlantic Ocean2.7Aug. 21, 2017 … South Pacific Ocean5.3July11, 2010 India, China, South Pacific6.6July 22, 2009 Arctic Ocean, Siberia, China2.4Aug. 1, 2008 Africa, Asia Minor, Russia4.1Mar. 29, 2006 South Pacific Ocean0.7April 8, 2005 Antarctica2.0Nov. 23, 2003 South Africa, Australia2.1Dec. 4, 2002 Where VisibleDuration of Totality (minutes) Date Solar Eclipse – Ground tracks Lunar Eclipse n The Earth is between the Sun and the Moon (Full Moon) n The Earth’s shadow is much larger and lunar eclipses are visible from anywhere on the night side of Earth n So, lunar eclipses are much more common n Total eclipses every 2-3 years, partials more often. n Totality lasts up to 1 hour 40 minutes