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Summer Constellations. Dr. Christopher Sirola Department of Physics & Astronomy University of Southern Mississippi. Contents. Introduction to Constellations Coordinate Systems Locating Objects A Few Stories A Few Objects. Introduction to Constellations.
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Summer Constellations Dr. Christopher Sirola Department of Physics & Astronomy University of Southern Mississippi
Contents Introduction to Constellations Coordinate Systems Locating Objects A Few Stories A Few Objects
Introduction to Constellations The word “constellation” is a combination of “con” (“with”, as in grouping) and “stella” (star). Modern constellations are official groupings of stars.
Constellations vs. Asterisms Similarly, an “asterism” is also a picture made of stars. So what’s the difference? An asterism is unofficial (as determined by astronomers)
Constellations vs. Asterisms The Big Dipper is an asterism; Ursa Major is a constellation.
Constellation Trivia There are 88 official constellations There is no part of the sky not covered by modern constellations Most northern hemisphere constellation names taken from ancient Greeks Many southern hemisphere constellations named by 15th & 16th century European sailors
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 EarthIn the Sky North Pole North Celestial Pole Equator Celestial Equator South Pole South Celestial Pole Longitude Right Ascension Latitude Declination Position of the Sun Ecliptic
Ecliptic (path of the Sun) Celestial Equator NCP Earth SCP
Declination (latitude) Right Ascension (longitude)
Declination Like latitude North-south position Uses degrees (like Earth latitude) Goes from +900 (NCP) through 00 (CE) to – 900 (SCP) Celestial Coordinates Right Ascension Like longitude East-west position Divides full circle into 24 “hour angles” rather than 3600 Thus an object moves one hour per hour Goes from 0 to 24h
Can you locate some bright stars? RA (h m)Dec (deg)StarConstellation 6 45 - 16 Sirius Canis Major 18 36 + 39 19 51 + 9 20 41 + 45 16 21 - 25 14 16 + 19
Can you locate some bright stars? RA (h m)Dec (deg)StarConstellation 6 45 - 16 Sirius Canis Major 18 36 + 39 Vega Lyra 19 51 + 9 Altair Aquila 20 41 + 45 Deneb Cygnus 16 21 - 25 Antares Scorpius 14 16 + 19 ArcturusBoötes
Global vs. Local The Celestial Sphere is a global system, used by everyone everywhere on Earth. What do we use when we wish to find objects in one’s own sky?
Local Coordinates TermMeaning Horizon Divides Earth from sky Zenith Point directly above one’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)
zenith Alt-Azimuth Coordinates meridian To NCP E W S N horizon
Alt-Azimuth Coordinates altitude E W S N azimuth
Stories Why do constellations exist? Sometimes look like pictures Help people find their way in the sky Cosmological significance Stories of heroes Historical stories
Example: Lyra the Harp Lyra is a harp, a stringed instrument held in one hand & plucked by the fingers of the other hand. Why would it be in the sky?
Example: Lyra the Harp In oral societies like ancient Greece, traveling musicians spread stories & shared culture. A Greek musician would sing or recite poetry (like Homer’s Iliad) to music.
Lyra the Harp Orpheus was the son of Apollo and the muse Calliope Orpheus was regarded as the best musician ever Orpheus was wedded to a lady named Eurydice in an outdoors ceremony Eurydice was bitten by a snake & died from the poison
Lyra the Harp Orpheus travels to the underworld to plead for Eurydice’s life before the throne of Hades
Lyra the Harp Hades allows Eurydice to leave, provided Orpheus doesn’t look for her until they are completely back in the world of the living.
Lyra the Harp Orpheus looked back just before the exit; Eurydice vanished.
Lyra the Harp Years later, Orpheus falls afoul of a local king The king throws Orpheus into a pit of snakes without his harp
Lyra the Harp Orpheus charms the snakes with his voice alone… … except for the deaf snake… Orpheus’ harp had been thrown into a nearby stream The music leaked out as the babbling of brooks
Lyra the Harp Vega is very bright Look for Vega near the zenith around midnight during the summer Vega is white in color Vega is near a parallelogram of medium-bright stars (forming the strings of the harp) How can we locate Lyra in the night sky?
Vega Fun facts about Vega 5th brightest star in night sky Original zero point for astronomical magnitude (brightness) system Normal (“Main Sequence”) star like the Sun, except a little bigger & brighter (Type A0 V) Was the North Star about 13,000 years ago (and will be so again in another 13,000 years!)
Other Summer Constellations • Cygnus (the swan) • Aquila (the eagle) • Hercules • Corona Borealis (the crown) • Bootes (the hunter) • Scorpius (the scorpion) • Sagittarius (the archer) • Ophiuchus (the doctor) Would you like to hear about any of these? (if time allows)
