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Ast 111

by: Rupak Kadel
Rupak Kadel
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About this Document

astronomy Lesson 1. Constelation and Units of Time
General Astronomy
Christopher Sirola
Class Notes
AST, astronomy, ast111, constellation, time, EARTH, Mars, week




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This 104 page Class Notes was uploaded by Rupak Kadel on Friday September 9, 2016. The Class Notes belongs to AST 111 at University of Southern Mississippi taught by Christopher Sirola in Fall 2016. Since its upload, it has received 32 views.


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Date Created: 09/09/16
Units of Space: Local Coordinates What do we do when we wish to lo▯ate o▯je▯ts i▯ o▯e’s o▯▯ sk▯? Local (Alt-Azimuth) Coordinates zenith meridian To NCP W S N horizon E Local Coordinate T erms Term Meaning Horizon Divides Earth from sky Zenith Poi▯t di▯e▯tl▯ a▯o▯e o▯e’s head Meridian Divides east from west on sky Altitude Angle of object above horizon (from 0 to 90 degrees) Azimuth Angle of object around horizon (measured east or west from due north, from 0 to 180 degrees) Alt-Azimuth Coordinates altitude W S N E azimuth Let’s ▯otate the pi▯tu▯e so No▯th is to our backs & South is in front of us. zenith meridian E S W horizon N Objects rise in the East & set in the West, including the Sun. local meridian E S W N ▯Lo▯al ▯oo▯▯ - not necessarily noon on the clock - occurs when the Sun crosses the local meridian. local meridian E S W N a.▯. = ▯a▯te ▯e▯idia▯▯: Whe▯ the “u▯ is East of (before) the local meridian. p.▯. = ▯post ▯e▯idia▯▯: Whe▯ the “u▯ is West of (after) the local meridian. local meridian E S W N Activity #1 A simple device used to measure angles on the sky is an astrolabe. You need: A protractor (with a hole at its origin); a straw (and tape to hold it); a loop of string; and a weight. Activity #1 altitude Use the astrolabe to sight in an object above the horizon by looking through the straw. Global vs. Local Alt-azimuth is a local system, used at o▯e’s o▯▯ lo▯atio▯ o▯ Ea▯th. What do we do when we wish to compare our observations with others? Constellations The ▯o▯d ▯▯o▯stellatio▯▯ is a ▯o▯▯i▯atio▯ of ▯▯o▯▯ ▯▯▯ith▯, as i▯ g▯oupi▯g▯ a▯d ▯stella▯ ▯sta▯▯. Modern constellations are official groupings of stars. Constellations vs. Asterisms “i▯ila▯l▯, a▯ ▯aste▯is▯▯ An asterism is also a picture made is unofficial of sta▯s. “o ▯hat’s the (as determined difference? by astronomers) Constellations vs. Asterisms The Big Dipper is an asterism; Ursa Major is a constellation. Space in 3 dimensions. What we see as a flat sky (Celestial Sphere) is actually a projection. Each star has its own distance from us as well as its angular coordinates. Constellation T rivia • There are 88 official constellations that cover all areas of the sky (set by the International Astronomical Union in 1929) • Most northern hemisphere constellation names taken from ancient Greeks • Many southern hemisphere th th constellations named by 15 & 16 century European sailors Units of Space: Celestial Coordinates Recall coordinates used on Earth: • Longitude measures east-west • Latitude measures north-south • Poles & equator define system The Sky is nicknamed the Celestial Sphere On Earth In the Sky North Pole North Celestial Pole Equator Celestial Equator South Pole South Celestial Pole Longitude Right Ascension Latitude Declination Path of the Sun Ecliptic NCP Ecliptic (path of the Sun) Celestial Equator The Celestial SCP Earth Sphere Declination (latitude) The Celestial Sphere Right Ascension (longitude) Celestial Coordinate T erms Right Ascension Declination • Like longitude • Like latitude • East-west position • North-south position • Divides full circle • Uses degrees i▯to ▯▯ ▯hou▯ a▯gles▯ rather than 3600 (like Earth latitude) • Goes from +90 (NCP) • Thus an object moves through 0 (CE) one hour per hour to – 90 (SCP) • Goes from 0 to 24 h Units for hour angles 60 arcminutes per degree 1º 1'' 360º for a 60 arcseconds complete per arcminute circle 1' Sirius: RA 6 hours 45 minutes, Dec – 16 degrees Sirius: RA 6 hours 45 minutes, Dec – 16 degrees Coordinates of well-known stars RA (h m) Dec (deg) Star Constellation 2 32 + 89 Polaris Ursa Minor 3 5 + 40 Algol Perseus 5 14 - 8 Rigel Orion 5 55 + 7 Betelgeuse Orion 4 36 + 17 Aldebaran Taurus 3 24 + 50 Mirfak Perseus Activity #2: Retrograde Motion Let’s look at the ▯et▯og▯ade ▯otio▯ of Ma▯s by plotting its position on the sky over time. • We need to use global coordinates • Right Ascension (celestial longitude) will be on the horizontal axis, increasing to the left • Declination (celestial latitude) will be on the vertical axis, increasing up Activity #2: Retrograde Motion 20 Here is an example of how to scale your graph. The dashed line is the 10 ecliptic. Let’s plot a sa▯ple poi▯t: 0 12h 11h 10h 9h Activity #2: Retrograde Motion 20 RA = 8.7 h Dec = +19.6 10 0 12h 11h 10h 9h Activity #2: Retrograde Motion The finished plot should 20 look something like this: 10 0 12h 11h 10h 9h Activity #2: Retrograde Motion Sketch a curve in order 20 of time. 10 Did Mars appear to move backwards for a while? 0 12h 11h 10h 9h Units of Time Many (not all) of our basic units of time have astronomical origins. Astronomical clock from Prague Units of Time: The Day Imagine it is local noon on the Earth. The Sun is at the local meridian and behind it are background stars. Earth Sun Note the picture is not to scale. Specifically, the stars are actually very far to the right. Background stars The Day The Earth has 2 basic motions: 1. It rotates on its axis 2. It orbits the Sun The Day Let’s follo▯ its ▯otio▯s th▯ough ¼ of a turn at a time. The Ea▯th ▯ill spi▯… … ▯ut ▯oti▯e ▯hat happe▯s as it does. The Day The Day The Day The Day The Day The Day Because the Earth rotates and orbits at the same time, a full spin does not bring it back into alignment with the Sun. The Day The Earth needs to orbit and rotate a bit more in order to align with the Sun again. The Day When the Earth has made a complete spin with respect to the stars, we call that a sidereal day. A sidereal day lasts 23 hours, 56 minutes, 3.92 seconds The Day A complete spin that brings the Sun back to the local meridian is called a solar day. A solar day lasts our familiar 24 hours. The Day Note the apparent position of the Sun has shifted to the East (by slightly less than 1 degree). ~ 1° The Day In fact, the degree symbol ( ° ) originally stood for the Sun. ~ 1° Compare the number of days per year to the number of degrees in a full circle. Units of Time: the Month The orbit (and phases) of the Moon behave similarly. Moon Earth Sun Again, the figure is not to scale. Background stars The Month A ▯▯e▯▯ Moo▯ o▯▯u▯s when the Moon is between the Earth and Sun. The red oval represents the Moo▯’s o▯▯it a▯out the Ea▯th. The Month Let’s ▯at▯h the Moo▯ orbit the Earth as the Earth orbits the Sun. We ▯ill depi▯t the Moo▯’s appearance from Earth here: The Month Note the Moon is not visible du▯i▯g its ▯▯e▯▯ phase. Each step lasts ~ 3 ½ days. New The Month New The Month Waxing Crescent The Month First Quarter The Month Waxing Gibbous The Month Full The Month Waning Gibbous The Month Third (last) Quarter The Month Waning Crescent The Month New The Month Note again that the Earth had to move an extra distance to return to its starting point. The Month The Moo▯’s o▯▯ital pe▯iod with respect to the stars is called its sidereal period. The Moo▯’s side▯eal pe▯iod is about 27 1/3 days long. The Month The Moo▯’s o▯▯ital pe▯iod with respect to the Sun is called its synodic period. The Moo▯’s s▯▯odi▯ pe▯iod is about 29 ½ days long. The Month The phases of the Moon track its synodic (solar) period. Units of Time: The Calendar Nut, goddessn of the sky. Our calendar hails from the Egyptians, who noted 360 days + 5 festival days at the end of the year . The Calendar However , this is too short. So after a few centuries, the Egyptian calendar was out of whack with the seasons. The Calendar When Julius Caesar took over the Roman Republic, he adopted the Egyptian calendar, but made a correction. A ▯leap da▯▯ ▯as added e▯e▯▯ fourth year to keep the calendar in line with the seasons. The Calendar But ¼ of a day is slightly too long. The seasons were seriously out of whack again by the 1500s. Pope Gregory XIII’s ast▯o▯o▯e▯s made one final alteration: Subtract 3 leap days every 4 centuries. This is the calendar we use today. Units of Time: The Seasons The Ea▯th’s ▯otatio▯al a▯is is tilted ▯▯ ▯▯ ½ degrees relative to the plane of its orbit. The Seasons This means different parts of the Earth are facing the Sun in different seasons. Spring Summer Winter Autumn (Seasons are cited for the Northern Hemisphere) The Seasons Summer happens when that side (north or south) tilts toward the Sun; winter when that side tilts away. incoming sunlight The Seasons Spring Equinox: March21 Summer Solstice: June 21 Autumnal Equinox: Sept. 21 Winter Solstice: Dec. 21 Spring Summer Winter Autumn E▯ui▯o▯ = ▯E▯ual Night▯ “olsti▯e = ▯“u▯ “ta▯d “till▯ Units of Time: The Week The origins of the Day, Month, and Year a▯e ▯ell k▯o▯▯… ▯ut ▯hat a▯out the Week? • What is a week? • Why 7 days long? • Who came up with it? • Where do the names of the days come from? The Week One possibility is that the week ultimately comes from ancient Babylonians. 1 Quarter Full 3 Quarter New They observed holy days at each successive major phase of the Moon. The Week They counted 7-day weeks from the New Moon, then reset at the next New Moon. 7 days 14 days 21 days 29-30 days The fi▯al ▯▯eek▯ ▯ould last 8-9 days. The Week This ▯o▯thl▯ ▯▯▯le ▯as ▯alled ▯sappatu▯ . 7 days 14 days 21 days 29-30 days Ou▯ ▯o▯d ▯▯eek▯ ▯o▯es f▯o▯ a▯ old E▯glish ▯o▯d fo▯ ▯▯ha▯ge▯ . Co▯pa▯e the Ge▯▯a▯ ▯woche▯ ▯▯eek▯ ▯ith ▯wechsel▯ ▯▯ha▯ge▯. The Week Babylonian astronomers also recognized seven objects that move relative to the stars. The Week The▯ ▯a▯e to ▯e ▯alled ▯pla▯ets, afte▯ the a▯▯ie▯t G▯eek ▯o▯d fo▯ ▯▯a▯de▯e▯s▯. The Week Our names of the days come mostly from old Germanic/Nordic deities. The Week Sunday is named after the Sun, of course. Mani & Sol The Norse goddess of the Sun was Sol. The Week And Monday is named for the Moon. The Norse god Mani & Sol of the Moon was Mani. The Week Tuesday is named for Tiw or Ty, a Norse god of war & bravery. Tyr His planet was Mars. The Week Wednesday is named for Woden or Odin, the chief of the Odin riding his Norse gods. 8-legged horse, Sleipnir His planet was Mercury. The Week Thursday is named for Thor , the Norse god of thunder . His planet Thor was Jupiter. The Week Thor has been a character in comics and now in movies. Chris Hemsworth as Thor The Week Friday is named for Frigga or Freya, a Norse goddess of Frigga weaving love & beauty. the clouds Her planet was Venus. The Week Saturday is the only non-Nordic day of the week. Saturn was an elder god in the Greco-Roman Saturn tradition. The Week Go back some 26 centuries. Judah had been conquered and its population exiled to Bablyon. Map of Neo-Babylonian Empire c. 600 BCE. The Week The Jewish people found themselves in a land with a 7-day week. They already had a similar Map of Neo-Babylonian Empire tradition: c. 600 BCE. The Week In Genesis, the world is created in six days, with the 7 set aside as a day of rest. Do you recall the designation given 1 Day of creation th (Nuremberg Chronicle, to the 7 day? 1493) The Week The Babylonian word ▯sappatu▯ a▯d the ▯o▯d ▯sabbath▯ sha▯e the same linguistic origin. At right – reconstruction of a Torah scroll, at a synagogue in Cologne, Germany. Units of Time (sort of): Eclipses The Moon cuts between the Earth & Sun once every month – so ▯h▯ do▯’t ▯e ha▯e a monthly solar eclipse? Eclipses Likewise, the Moon moves behind the Ea▯th o▯▯e pe▯ ▯o▯th, ▯et ▯e do▯’t see a monthly lunar eclipse either. Eclipses The pla▯e of the Moo▯’s o▯▯it is tilted by 5° ▯elati▯e to the Ea▯th’s o▯▯it. This means the Moon is usually above or below the Earth. Eclipse terms Solar eclipse: When the Sun is covered Lunar eclipse: When the Moon is covered Solar eclipse Lunar eclipse Eclipse terms Total: All of object is covered Annular: Most of object is covered Partial: Some of object is covered Total Annular (ring) Partial Eclipses A lunar eclipse is visible from Earth one to two times per year and can last for hours. What is the phase of the Moon during a lunar eclipse? Eclipses Solar eclipses only occur about once every other year and last up to a maximum of just 7 minutes. What is the phase during a solar eclipse? Eclipses The Moo▯’s o▯▯it is ▯ot pe▯fe▯tl▯ circula, so sometimes it is closer & sometimes further away. When the Moon is far enough away, we can have an annular solar eclipse. A total solar eclipse will next hit the United States on August 21, 2017. Unfortunately, it will miss Mississippi. The thin blue line shows the umbral part of the eclipse; the rest is the penumbral part. The umbra is the darkest part of the shadow; the penumbra the lighter part of the shadow. Penumbral Umbral Penumbral Here is the edge of the eclipse for St. Louis.


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