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Download Basic Patterns and Motions in the Sky
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Daniel Fischbach Physics 202-004 – Astronomy 6/17/17 Created on: 1/21/05 Topic: Basic Patterns and Motions in the Sky Latitude – Angle North of South of the equator (+90º to –90º) Longitude – Angle around the Earth running from 180º East to 180º West (not parallel to one another) North and South (Terrestrial) Poles have undefined longitudes Terrestrial Equator – 0º latitude Horizon – boundary between Earth and sky (gigantic circle surrounding you) Celestial Sphere – Imaginary sphere that you are at the center at and everything in the Universe is “painted” on it Horizon Coordinates (on the Celestial Sphere): o Altitude – Angle above or below the horizon Above: + (you can see it) Middle: 0º (The horizon itself) Below: – (you can’t see it) o Azimuth – Angle around the celestial sphere: North: 0º/360º azimuth East: 90º azimuth South: 180º azimuth West: 270º azimuth These 4 direction can be labeled on the horizon as North, East, South, and West Points o Zenith: Altitude: +90º (undefined azimuth) o Nadir: Altitude: –90º (undefined azimuth) Professional astronomers almost never use horizon coordinates Horizon coordinates only apply to your current location Everything in the sky does not have a fixed set of horizon coordinates because the Earth is rotating The Sun (and everything else) rises in the East and sets in the West Meridian – A giant circle that starts at the North Point, goes through the Zenith, goes through the South Point, goes through the Nadir, and goes back to the North Point Rising – Crosses horizon at the East (0º altitude) – Example: Sunrise Culmination/Transiting – Crosses the meridian – Examples: Noon and Midnight Setting – Crosses horizon at the West (0º altitude) – Example: Sunset AM – Anti Meridian PM – Post Meridian We should not be using horizon coordinates Equatorial coordinates: o Right ascension – Like longitude on the Earth but on the Celestial Sphere (not parallel to one another) – Measured in hours – 15º is an hour o Declination – Like latitude on the Earth but on the Celestial Sphere o Celestial Equator – Equator on the Celestial Sphere (at 0º Declination) North Celestial Pole: Declination: +90º (undefined right ascension) South Celestial Pole: Declination: –90º (undefined right ascension) 841167377 Instructor: Libarid A. Maljian Page 1 of 10 Daniel Fischbach Physics 202-004 – Astronomy 6/17/17 North and South Celestial Poles are located where the North and South Terrestrial Poles are located You can only find true North via the North Star (a compass only finds magnetic North) You can find out the latitude of your location (and the cardinal directions) via the altitude of the North Star Circumpolar stars – Stars that run around the North Star (and the South Star if there were one) Circumpolar constellations: o The Big Dipper – 7 stars (part of Ursa Major, “The Big Bear”, both below) o Light pollution – A glow around the atmosphere that prevents us from seeing faint stars o The North Star is not the brightest star 841167377 Instructor: Libarid A. Maljian Page 2 of 10 Daniel Fischbach Physics 202-004 – Astronomy 6/17/17 841167377 Instructor: Libarid A. Maljian Page 3 of 10 Daniel Fischbach Physics 202-004 – Astronomy 6/17/17 Instructor: Libarid A. Maljian Page 4 of 10 o Cygnus the sawn 841167377 Daniel Fischbach Physics 202-004 – Astronomy 6/17/17 Instructor: Libarid A. Maljian Page 5 of 10 o Northern Cross 841167377 Daniel Fischbach Physics 202-004 – Astronomy 6/17/17 Instructor: Libarid A. Maljian Page 6 of 10 Summer Constellations o Orion o Taurus 841167377 Daniel Fischbach Physics 202-004 – Astronomy 6/17/17 o The Pleiades o Canis Major – Sirius is the brightest star in the entire sky (besides the Sun) o Canis Minor 841167377 Instructor: Libarid A. Maljian Page 7 of 10 Daniel Fischbach Physics 202-004 – Astronomy 6/17/17 o Gemini – The Twins and Cancer – The Crab 841167377 Instructor: Libarid A. Maljian Page 8 of 10 Daniel Fischbach Physics 202-004 – Astronomy 6/17/17 Instructor: Libarid A. Maljian Page 9 of 10 o Leo – The Lion 841167377 Daniel Fischbach Physics 202-004 – Astronomy 6/17/17 o Virgo – The Virgin The Ecliptic – The imaginary path followed by the Sun around the celestial sphere. Astrological signs (zodiac constellations) pass through these All of the Zodiac constellations are one month off 841167377 Instructor: Libarid A. Maljian Page 10 of 10