Astro101 Navigating the Night Sky

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Information about Astro101 Navigating the Night Sky

Published on August 21, 2007

Author: Abbott


Astro 101:Navigating the Night Sky:  Astro 101: Navigating the Night Sky presented by Paul Winalski 20 April 2007 Topics for this Evening:  Topics for this Evening Celestial Coordinates Star Nomenclature Orientating One’s Self to the Sky Star-hopping Reading Star Charts The Universe’s Four Dimensions:  The Universe’s Four Dimensions At 90-degree angles to each other Distance (forward/backward) Azimuth (left/right) Altitude (up/down) Time (past/future) Coordinate Systems:  Coordinate Systems Two basic kinds Measure from a point of reference (origin) Cartesian: linear measure in all dimensions Example: two blocks forward, left three blocks, up ten stories, two hours from now Not useful for the sky (objects too far away) Polar Distance and Time by linear measure Altitude and Azimuth by angular measure Polar Altazimuth Concepts:  Polar Altazimuth Concepts Angles measured in degrees (º) of arc 360º in entire circle, or ± 180º from origin 60 minutes of arc (60') per degree 60 seconds of arc (60') per minute Zenith (direction overhead; +90º altitude) Nadir (direction underneath; -90º altitude) Horizon (great circle at 0º altitude) Azimuth measured starting 0º due north, east positive, west negative Polar Altazimuth Coordinates:  Polar Altazimuth Coordinates Zenith Horizon Azimuth Altitude Distance Motion of the Earth:  Motion of the Earth Rotation: once around the N/S polar axis every 24 hours Revolution about the Sun: once every 365.25 days Precession (wobbling of polar axis): in 47º circle once every 25,800 years Nutation (a shorter period wobbling): not very significant to us Relativity:  Relativity Newtonian Relativity Observation: only CHANGE in momentum (motion in a linear direction) can be detected Conclusion: position and motion are relative to the observer (frame of reference) Einsteinian Relativity Observation: the speed of light in a vacuum is the same for all observers Conclusion: passage of time is relative to the observer Invoking Relativity:  Invoking Relativity Our motion rotational speed: 800 mph average revolutionary speed: 66,622 mph Nearly constant motion; change in direction insignificantly small (at our scale) Thus we seem to be standing still By Newtonian Relativity, it’s valid to say that the sky moves around us The Celestial Sphere:  The Celestial Sphere We are on the Earth’s surface Earth’s radius (4000 mi) is insignificant compared to stellar distances (25 trillion miles to nearest star) So we can simplify: move our origin to the center of the Earth ignore distance and deal only in altitude/azimuth Equatorial Coordinate System:  Equatorial Coordinate System Polar coordinate system, equivalent to geographic coordinate system Celestial poles aligned with geographic poles of the Earth’s rotation Independent of local latitude/longitude (unlike altazimuth coordinates) Important Celestial Great Circles:  Important Celestial Great Circles Horizon: at 0º local altitude Meridian: intersecting local zenith and equatorial poles Celestial Equator: at 90º to meridian Ecliptic: intersecting plane of Earth’s orbit about the Sun (at 23.5º angle to equator) Galactic Equator: intersecting center plane of Milky Way galaxy’s spiral arms Equinoxes:  Equinoxes Intersection points between equator and ecliptic Vernal Equinox ('first point of Aries'): position of Sun passing from Southern to Northern Hemisphere (our first day of Spring) Autumnal Equinox: position of Sun passing from Northern to Southern Hemisphere (our first day of Fall) Declination and Right Ascension:  Declination and Right Ascension Declination (Dec): 'latitude' angle north (positive) or south (negative) from celestial equator; divided into degrees, minutes, seconds of arc Right Ascension (RA): 'longitude' angle measured along equator east from vernal equinox divided into 24 hours (15º of arc each) each hour into 60 minutes (15' of arc each) each minute into 60 seconds (15' of arc each) Ecliptic Coordinate System:  Ecliptic Coordinate System Used in many sky atlases from the 1600s Polar coordinates Ecliptic is 0° latitude Poles are North and South Ecliptic Poles Longitude measured 0-360° from classical First Point of Aries Independent of Precession (but not nutation) No significant advantage over Equatorial System Galactic Coordinate System:  Galactic Coordinate System Polar coordinates 0° Latitude is galactic equator (mid line of Milky Way) Poles are North and South Galactic Poles Longitude measured 0-360° from galactic center Galactic Equator and Poles:  Galactic Equator and Poles Equator Poles Local Measure:Position Angle and Separation:  Local Measure: Position Angle and Separation Origin is primary object Degrees / Minutes / Seconds of arc Position angle measured eastward from North Separation likewise measured as an angle Example: Double Star Albireo N Separation=34.3' Position Angle=54° Local Measure Yardsticks:  Local Measure Yardsticks Across top of 'bowl' of Big Dipper: 10° Across bottom of 'bowl' of Dipper: 8° Across end of 'bowl' of Big Dipper: 5° Across end of 'bowl' of Little Dipper: 3º Diameter of Moon: 0.5º (30') Telrad: 4°, 2°, ½º Rigel QuikFinder: 2°, ½º Learn field width of your finder and eyepieces More Local Measure YardsticksDistance with Arm Outstretched:  More Local Measure Yardsticks Distance with Arm Outstretched Width of index finger: 2° Across clenched fist: 10° From end of thumb to end of pinky with hand stretched wide: 30º Motion of Sky Objects:  Motion of Sky Objects Daily rotation: 360º of arc (24 hours of right ascension) about the celestial poles per day; 15º of arc per hour Culmination: when an object crosses the meridian Sidereal Time: current right ascension coordinate of the meridian Annual revolution: 360º of arc in 365.25 days, about 4 minutes of right ascension per day Therefore: Sidereal day is 4 minutes shorter than the chronological day Precession:  Precession Wobble of the Earth’s axis Poles move in a 47º circle over 25,800 year period Changes orientation of equatorial coordinate system Pole star changes (Thuban  Polaris  Vega) Vernal equinox ('first point of Aries') is now in Pisces; moving westward into Aquarius Tropics of Cancer/Capricorn are really Gemini/Sagittarius today Star charts change orientation or Epoch (1920 vs. 1950 vs. 2000) over time Slide23:  Proper Motion:  Proper Motion Motion of close stars relative to distant background stars Very slow except for a few close stars (Proxima Centauri, Barnard’s Star) Only significant over centuries and millennia The Sky Looks Confusing...:  The Sky Looks Confusing... Constellations:  Constellations Patterns of bright stars in the sky IAU-designated boundaries, marking out specific sky regions Named in Latin, mostly from ancient times There are 88 of them in all 53 are visible from our latitude About 20 or so are worth learning Bringing Some Order to Chaos...:  Bringing Some Order to Chaos... Star Nomenclature:  Star Nomenclature Proper (individual) Names Bayer Letters Flamsteed Numbers Variable Star Designations Double Star Lists and Catalogues Professional Catalogues Proper Names:  Proper Names Different in different languages English names generally based on Greek, Latin, Arabic Only the brightest stars have proper names in common use Multiple stars have suffix A, B, C, etc. applied to components in order of apparent brightness Bayer LettersUranometria, 1603:  Bayer Letters Uranometria, 1603 Greek lower case letter α - ω followed by genitive of Latin constellation name (e.g., α Centauri), allowing for 24 designations Usually assigned in order of apparent brightness, but not always If more needed, lowercase Roman (a - z) and then uppercase Roman (A - Q) [these are not in use anymore] The Greek Lowercase Alphabet:  The Greek Lowercase Alphabet α Alpha β Beta γ Gamma δ Delta ε Epsilon ζ Zeta η Eta θ Theta ι Iota κ Kappa λ Lambda μ Mu ν Nu ξ Xi ο Omicron π Pi ρ Rho σ Sigma τ Tau υ Upsilon φ Phi χ Chi ψ Psi ω Omega Flamsteed Numbers:  Flamsteed Numbers Number + genitive of constellation name (e.g., 66 Geminorum) Assigned to stars from west to east Greek Bayer letters usually take precedence Argelander Variable Star Letters:  Argelander Variable Star Letters Upper case Roman Letters + genitive of constellation (e.g., R Leporis) Assigned in order of discovery of variability R - Z, RR - RZ, SS - SZ, TT - TZ, UU - UZ, VV - VZ, WW - WZ, XX - XZ, YY, YZ, ZZ Then AA - AZ, BB - BZ, etc. through QZ (but J never used) then V335, V336, ... Usually not assigned to stars with Bayer Greek letters Double Star Lists and Catalogues:  Double Star Lists and Catalogues F.G.W. Struve (Σ, Σ I, Σ II) Otto Struve (OΣ, OΣΣ) John Herschel (h) J. Dunlop (Δ) S.W. Burnham (β) T.J.J. See (λ) The Many Names of a Star:  The Many Names of a Star Proper name: Castor (A, B, C) Bayer: α Geminorum (Alpha Geminorum) Flamsteed: 66 Geminorum Variable (Castor C): YY Geminorum Multiple Star: Σ1110 (Struve 1110) Professional: GI 278, HR 2891, FKS 287, BD +32 1581/2, HD 60178/60179, SAO 60198, ADS 6175, HIP 36850, etc. The Magnitude System:  The Magnitude System Originally established by Hipparchus andamp; Ptolemy Magnitude = 'rank' or 'importance' 1st magnitude = brightest stars 6th magnitude = barely visible naked eye 5 magnitudes = 100x brightness Each order of magnitude = 2.512x brightness (fifth root of 100) The 21 First Magnitude Stars:  The 21 First Magnitude Stars Sirius (Canis Major), -1.42 Canopus (Carina), -0.72 Alpha Centauri (Centaurus), -0.27 Arcturus (Boötes), -0.06 Vega (Lyra), 0.04 Capella (Auriga), 0.06 Rigel (Orion), 0.14 Procyon (Canis Minor), 0.35 Achernar (Eridanus), 0.53 Hadar (Centaurus), 0.66 Betelgeuse (Orion), 0.70 Altair (Aquila), 0.77 Aldebaran (Taurus), 0.86 Acrux (Crux), 0.87 Antares (Scorpius), 0.92 Spica (Virgo), 1.00 Pollux (Gemini), 1.16 Fomalhaut (Piscis Austrinus), 1.17 Deneb (Cygnus), 1.26 Beta Crucis (Crux), 1.28 Regulus (Leo), 1.36 Polaris: The North Star:  Polaris: The North Star 2nd (1.99) magnitude star α Ursae Minoris ¾ degree of arc from celestial north pole Barely moves with time of day or season Its altitude = your geographic latitude Useful for aligning equatorial mounts A double star (Σ93) A cepheid variable star NH Constellations (53):  NH Constellations (53) Andromeda Aquarius Aquila Aries Auriga Boötes Camelopardalis Cancer Canes Venatici Canis Major Canis Minor Capricornus Cassiopeia Cepheus Cetus Coma Berenices Corona Borealis Corvus Crater Cygnus Delphinus Draco Equuleus Eridanus Gemini Hercules Hydra Lacerta Leo Leo Minor Lepus Libra Lynx Lyra Monoceros Ophiuchus Orion Pegasus Perseus Pisces Piscis Austrinus Puppis Sagitta Sagittarius Scorpius Scutum Serpens Taurus Triangulum Ursa Major Ursa Minor Virgo Vulpecula The Important Ones (24):  The Important Ones (24) Andromeda Aquila Auriga Boötes Canis Major Canis Minor Capricornus Cassiopeia Cepheus Cygnus Gemini Hercules Leo Lyra Ophiuchus Orion Pegasus Perseus Sagittarius Scorpius Taurus Ursa Major Ursa Minor Virgo The Zodiac:Where the Moon and Planets Are:  The Zodiac: Where the Moon and Planets Are Pisces Aries Taurus Gemini Cancer Leo Virgo Libra Scorpius Sagittarius Capricornus Aquarius Circumpolar Constellations:  Circumpolar Constellations Always above the horizon (though often very low) Everything with declination higher than 90º minus your latitude (90 - 43 = 47ºN for us) For us: Ursa Minor, Ursa Major, Cassiopeia, Cepheus, Camelopardalis, Draco, Lynx The Spring Sky:  The Spring Sky Constellations (12): Ursa Major, Ursa Minor, Cepheus, Cassiopeia, Perseus, Auriga, Taurus, Gemini, Orion, Canis Major, Canis Minor, Leo, Boötes Stars (11): Capella, Aldebaran, Betelgeuse, Rigel, Sirius, Adhara, Procyon, Regulus, Arcturus, Castor, Pollux Asterisms, etc.: Pleiades, Hyades Slide44:  21 March 2007 10:00 PM The Summer Sky:  The Summer Sky Constellations (15): Cepheus, Ursa Minor, Ursa Major, Cygnus, Leo, Boötes, Hercules, Corona Borealis, Lyra, Aquila, Ophiuchus, Virgo, Scorpius, Hydra, Corvus Stars (9): Deneb, Vega, Altair, Arcturus, Regulus, Spica, Antares, Castor, Pollux Asterisms, etc.: 'Keystone' of Hercules; 'Summer Triangle' Slide46:  21 June 2007 9:00 PM The Autumn Sky:  The Autumn Sky Constellations (19): Ursa Major, Ursa Minor, Cassiopeia, Cepheus, Boötes, Hercules, Corona Borealis, Lyra, Cygnus, Aquila, Delphinus, Ophiuchus, Sagittarius, Capricornus, Aquarius, Piscis Austrinus, Pisces, Pegasus, Andromeda Stars (5): Arcturus, Vega, Deneb, Altair, Fomalhaut Asterisms, etc.: 'Summer Triangle', 'Keystone' of Hercules, 'Great Square' of Pegasus, 'Teapot' of Sagittarius, 'Water Jar' of Aquarius, 'Circlet' of Pisces Slide48:  21 September 2007 9:00 PM The Winter Sky:  The Winter Sky Constellations (16): Ursa Major, Ursa Minor, Cepheus, Cassiopeia, Perseus, Andromeda, Pegasus, Cetus, Pisces, Auriga, Aries, Taurus, Orion, Canis Minor, Canis Major, Gemini Stars (9): Vega, Deneb, Aldebaran, Betelgeuse, Rigel, Sirius, Procyon, Castor, Pollux Asterisms, etc.: 'Great Square' of Pegasus, 'Circlet' of Pisces, Pleiades, Hyades Slide50:  21 December 2007 9:00 PM Star Hopping:  Star Hopping Finding objects without artificial aid Use the major guideposts to orient the sky Follow pointers to zero in on the destination Star Hop to M31, M32, M110:  Star Hop to M31, M32, M110 Find the Great Square of Pegasus Northeast corner is Alpha Andromedae Count two stars along each 'string' of Andromeda Follow 'pointers' north the same distance, and there you are Slide53:  Telescopic Star Hop:NGC 2261 (Hubble’s Variable Nebula):  Telescopic Star Hop: NGC 2261 (Hubble’s Variable Nebula) Locate Gemini Go to 'foot of Pollux': ξ (Xi) Geminorum Move south to NGC 2264 ('Christmas Tree' Cluster) South to double star Σ953 (Struve 953) Southwest to Hubble’s Variable Nebula Slide55:  Slide56:  Slide57:  2º View Solar System Guideposts:  Solar System Guideposts 5 Naked-eye Major Planets Mercury, Venus, Mars, Jupiter, Saturn Very bright (1st magnitude or brighter) Earth’s Moon (magnitude -12.6 when full!) They move relative to the stars Your geographic position may be significant Orbital Motion of Planets and Moon:  Orbital Motion of Planets and Moon Orbital planes all very near Ecliptic Direct motion: west to east Retrograde motion: east to west (when we 'pass' an outer planet in our orbit) Mercury and Venus shuttle back and forth across the Sun’s position Significant Planetary Positions:  Significant Planetary Positions Conjunction: both objects at same RA Opposition: objects 12 hours apart in RA Quadrature: objects 6 hours apart in RA Transit: smaller object passes across larger object’s disk Occultation: larger object hides smaller one Eclipse: shadow of one object hides another Solar Conjunction:  Solar Conjunction Culmination at local Noon Inner planets do it twice: Superior Conjunction: opposite side of Sun Inferior Conjunction: same side of Sun For our Moon, is called New Moon Planet/Moon not visible near conjunction Solar Opposition:  Solar Opposition Midnight culmination Not possible for inner planets; closest they get is Greatest Elongation Eastern (furthest away from Sun at evening twilight) Western (furthest away from Sun at morning twilight) For our Moon, is called Full Moon Outer planets at their brightest (because at their closest) Generally best time to observe outer planets Slide63:  Sun Earth Greatest Eastern Elongation Inferior Conjunction Superior Conjunction Opposition Conjunction Eastern Quadrature Observing Resources:  Observing Resources Planisphere Sky and Telescope magazine Celestial Atlases (Sky Atlas 2000.0) Software (The Sky, Sky Tools) Web Sites Heavens Above ( CalSKY ( Using a Sky Atlas:  Using a Sky Atlas Very much like reading a map Useful for plotting difficult star hops - online star atlas prints finder charts at many angular diameters charts oriented for your latitude/longitude/time of night planetary/moon positions and motions plotted Questions?:  Questions?

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