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 15 th & 16 th 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 PoleNorth Celestial Pole EquatorCelestial Equator South PoleSouth Celestial Pole LongitudeRight Ascension LatitudeDeclination Position of the SunEcliptic

NCP SCP Celestial Equator Ecliptic (path of the Sun) Earth

Declination (latitude) Right Ascension (longitude)

Celestial Coordinates Right Ascension Like longitude East-west position Divides full circle into 24 “hour angles” rather than Thus an object moves one hour per hour Goes from 0 to 24 h Declination Like latitude North-south position Uses degrees (like Earth latitude) Goes from (NCP) through 0 0 (CE) to – 90 0 (SCP)

Sirius: RA 6 hours 45 minutes, Dec – 16 degrees

Can you locate some bright stars? RA (h m)Dec (deg)StarConstellation SiriusCanis Major

Can you locate some bright stars? RA (h m)Dec (deg)StarConstellation SiriusCanis Major VegaLyra AltairAquila DenebCygnus AntaresScorpius 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 HorizonDivides Earth from sky ZenithPoint directly above one’s head MeridianDivides east from west on sky AltitudeAngle of object above horizon (from 0 to 90 degrees) AzimuthAngle of object around horizon (measured east or west from due north, from 0 to 180 degrees)

Alt-Azimuth Coordinates E SN W zenith horizon meridian To NCP

Alt-Azimuth Coordinates E SN W altitude 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 How can we locate Lyra in the night sky? 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)

Vega: RA 18h 36m; Dec + 39 deg

The Summer Triangle: Vega, Deneb, Altair

Vega Fun facts about Vega 5 th 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)

Thanks, and clear skies!