The ABCs of Stargazing How would you describe to a friend the size of a sky object, its distance from a particular star, its brightness, or its location on the celestial dome? The ABCs of stargazing allow you to do just that! "A" is for angular size and distance Be sure to remember these handy references when discussing size or distance in the sky: • The moon spans 1/2º. It would take 360 "full moons" to reach from horizon to horizon! • The apparent width of the tip of your index finger on your extended arm is 2º. • The width of the bowl of the Big Dipper is 5º and the bowl's length is 10º. • Your clenched fist on your fully extended arm is 10º from side to side. • Your outstretched hand on your extended arm is 20º from the tip of the pinky to the tip of the thumb. Your fist Your index The Big Dipper 10º finder 2º 10º 5º Width of Moon's apparent size 3rd the Full relative to your Your hand Six of the seven stars Moon 1/2º clenched fist 20º of the Big Dipper are of the 2nd magnitude. "B" is for brightness Skywatchers use the "magnitude" scale to Mag. Object describe an object's brightness. Don't be -26 Sun (never look at the sun!) confused by the reverse nature of the scale: -12 Full moon The brighter the object, the smaller the -4 Venus magnitude. Objects with negative -2.5 Jupiter at its brightest magnitudes are very bright, indeed! -1.5 Sirius, the brightest star in the night 0Arcturus, Vega, Capella, Saturn Polaris, the North Star, always has an azimuth +1 Pollux, Regulus, Altair of 0º and has an altitude above the northern +2 Six stars of the Big Dipper, North Star horizon matching the latitude of the observer. +6 The faintest star seen by unaided eyes Zenith: North Star: Altitude = 90º Alt = Your Star: "C" is for coordinates Alt = 50º latitude Stargazers often use the simple, but Az = 0º Az = 150º descriptive altitude-azimuth (alt-az) system to locate objects in the sky. Horizon: Altitude = 0º E = 90º Azimuth coordinate: Altitude coordinate: North is 0º Horizon is 0º N = 0º East is 90º Zenith is 90º S = 180º South is 180º West is 270º The Astronomical League, W = 270º www.astroleague.org/outreach Azimuth How do you find celestial objects? Finding celestial targets the modern way Computerized "GoTo" telescopes ... the quick and easy method: 1 Level the telescope mount 5 Center on first guide star 2 Point the tube towards north 6 Center on second guide star 3 Indicate the date and time 7 Enter the target's designation 4 Indicate observing location 8 The scope automatically slews to it Finding celestial treasures the old fashioned way 1 Learn the stars Cassiopeia and constellations There is no subsitute for sitting under the stars with a map and red flashlight. Use a star map that plots all stars visible to the unaided eye. Start by finding well-known star patterns such as the Big Dipper, or the constellation of Orion or Cassiopeia. Continue by identifying neighboring star patterns. Target — NGC 7789 7789 2 Finderscope: little scope, big view Why a finderscope? β Cas Gives a wide field of view, about 5º, Must be aligned with the main telescope, Only the bright planets, brighter nebulae and star clusters are visible. Finderscope view, note the inverted image Simply... Point the finder at a suitable guide star, or Triangulate to the object by using nearby recognizable stars. The Big Dipper 3 Star Hopping: finding the faintest of objects... Eyepiece view Before hopping begins: of M108 β Must have a detailed star map. + Must know the field of view of the M108 eyepiece. As an example, find galaxy M108: Begin hopping at a reference star, in this case Beta ( β ) Ursa Majoris in the Big Dipper. Match the stars on the map with those in the eyepiece. Hope among the stars in each subsequent field of view until the correct field is reached. Look closely to see the dim galaxy M108. Star hopping to M108 from Beta Ursa Majoris The Astronomical League www.astroleague.org/outreach Is that a planet or a star? Three tell tale visual characteristics a planet: 1 A planet shines with a steady light, unless it is very close to the horizon. It doesn’t “twinkle,” while a star does. 2 A planet is always located near the ecliptic. Is that a planet or a star? Three tell tale visual characteristics3 A planet slowly a shiftsplanet: its position nightly with respect to the background stars. 1 A planet shines with a steady light, unless it is very close to the horizon. It doesn’t “twinkle,” while a star does. Sun appears in Leo next to its bright Sun appears in Virgo next to its star Regulus on August 23. 2 A planet Isis always that located a near planet the ecliptic. brightor stara Spica star? on October 17. Leo Three Is tellthat tale visual a planetcharacteristics or a planet: a star? Sun on 3 A planet slowly shiftsIs itsthat position a planet nightly with or respect a star?Sun to on the Virgo Mars on Cancer Is that a planet or a star? Oct. 17 Aug. 23 Celestial Sphere 1 Abackground planet shines stars. with a steady light, unless it isLibra very close to Oct. 17 Mars on Three tell tale visualThree tell characteristics taleThree visual tell characteristics tale visual a planet:characteristics of a planet: a planet: Ecliptic the horizon. It doesn’t “twinkle,” while a star does. Aug. 23 A planet shines with1. 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Abackground planet slowly stars. shifts itsOct. position 17 nightly with respectsystem to projectedthe background onto stars. Oct. 17 against the starry backdrop. Libra Ecliptic Mars on the celestial sphere.Sun appears in Leo next to its bright Earth Aug. Earth 23 In this case, Mars moves in A planet slowly shifts its position nightlySun with appears respectin Virgo next to itsto thestar Regulus on August 23. 3 bright star SpicaSun onappears October 17. in Leo next to its bright Aug. 23 Oct. 17 front of the stars of Cancer, Sun appears in Virgo next to its Leo background stars. Celestial Sphere star Regulus on August 23. then towards Leo. Sun on Sun on bright star Spica on October 17. Virgo Mars on Cancer The ecliptic denotes Oct. 17 MarsLeo Aug. 23 Celestial Sphere Libra Ecliptic Oct. 17 Mars on the plane of the solar The SUN Ecliptic: TheSun onapparentShifting position path of ofa planetAug. the 23 sun across the celestial sphere Sun on Sun appears in Leo next to its brightMars on Cancer system projected onto Virgo against the starry backdrop. Sun appears in VirgoOct. 17 next to its Aug. 23 Celestial Sphere Libra star Regulus on August 23. Oct. 17 Mars on brightthe star celestial Spica onsphere. October 17.The ecliptic EarthEcliptic denotes Earth In Marsthis case, Mars moves in the plane of the solar SUN Shifting position ofAug. a planet 23 system Aug.projected 23 onto Oct. 17 Leo front ofagainst the thestars starry of backdrop. Cancer, Celestial Sphere Mercury the celestial sphere. Earth Sun Earthon then towardsIn this case, Leo. MarsThe moves inInner Planets: Mercury and Venus Sun on Aug. 23 Oct. 17 Mars onfront of the stars of Cancer, Cancer Virgo Celestial Sphere Aug. 23 Celestial Sphere The eclipticOct. 17 denotes • Either low above western horizonMars in Oct. 17then towards Leo. Libra The Ecliptic: The apparent path of the sun across the celestial sphereWhenMars on Mercury or Venus move between the Earth and the plane of the solar The Ecliptic Ecliptic: The SUN apparent path of the sunShifting across position the celestial of a planetsphere the evening, or theAug. sun23 or when they orbit on the sun’s far side, they system projected onto • Low above the eastern horizon inagainst the the starry backdrop. the celestial sphere. In this case, Mars movesappear in near it in our day sky and can’t be seen. Mercury Mercury Earth Earth The Inner Planets: Mercury and Venus morning.Aug. 23The Oct. Inner 17 Planets: frontMercury of the starsand ofVenus Cancer, • Either low above western horizon in When Mercury or Venus move between the Earth and Celestial Sphere The ecliptic denotes Mars • Either low above western horizonthe evening,in • A or challenge to spot. the sun or whenthen they towards orbit on the Leo. sun’s far side, they the plane of the solar • Low above the eastern SUN horizon When in the Mercury or VenusShifting move between position the of Eartha planet and the evening, or appear near it in our day sky and can’t be seen.