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Constellations In the Sky. Constellation: the pattern of stars seen in the sky, and refer to a specific region in the sky Ancient Astronomers named constellations: Mythological beings Heroes (Orion) Animals (Leo, Scorpio, etc .).
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Constellations In the Sky • Constellation:the pattern of stars seen in the sky, and refer to a specific region in the sky • Ancient Astronomers named constellations: • Mythological beings • Heroes (Orion) • Animals (Leo, Scorpio, etc.) • The stars that make up any constellation are not actually close together in space • They are bright enough to be observed with the naked eye • They happen to lie in the same direction in the sky as seen from Earth • Roughly 88 constellations in all • Most are visible from North America at some time during the year
Uses for Constellation • Navigation: Polaris (Located in Little Dipper): • Help indicate the direction of north and latitude • Constellations: • Help astronomers to specify large areas of the sky (geologists and continents) • Primitive calendars predicting/planning harvest and planting seasons. • Ancient cultures knew when certain stars appeared on the horizon before daybreak, it would be the beginning of spring http://my.execpc.com/60/B3/culp/astronomy/Winter/Bears.html
The Celestial Sphere • Celestial Sphere: surrounds the Earth, is a canopy of stars resembling an astronomical painting on a heavenly ceiling • APPARENT MOTION of stars is due to Earth’s rotation—the stars are not actually moving • Star Trails: show how all stars appear to move in circles around a point very close to the star Polaris http://www.perthnow.com.au/stunning-photographs-of-star-trails-over-outback-australia/story-e6frg4nl-1226411728115 http://www.bluemoon.bz/astrology/sun-ingress/libra/
The Celestial Sphere Celestial Poles: The points where Earth’s axis intersects the celestial sphere Celestial Equator: Midway between the north and south celestial poles Ecliptic – the apparent simple path the Sun takes as it circles the celestial sphere http://www.herongyang.com/astrology_horoscope/celestial_sphere.jpg
Milky Way • Only a whitish band can be seen on a clear night • Stretches all the way around the Celestial Sphere • Only see part at given time • Varies in width and has dark fissures running through • Band of light relationship to the Milky Way Galaxy • It traces the galactic plane as it appears from our location in the outskirts of the galaxy
The Dome of the Sky • Remember we only see ½ the celestial sphere at one time • (the ground beneath us blocks the rest of the view) • Local Sky- the sky as seen from wherever you happen to be standing • Horizon- the boundary between Earth and sky • Zenith- point directly over you head • Meridian- the imaginary ½ circle stretching from your horizon due south, through your zenith, to your horizon due north. • You can find the direction of any object by using the Azimuth and Altitude • Circumpolar-Stars never rise or set but make daily counterclockwise circles around the north celestial pole • Angular Size- is the angle it appears to span in your field of vie • Angular Distance- the angel that appears to separate them • Precise measurements: • Arcminutes- subdivide each degree into 60 • Arcseconds- subdivide each arcminute into 60
Zodiac • Zodiac-the constellations along the ecliptic • Why Do We See Different Constellations During the Year? • If observed through the year, the constellations shift gradually to the west. This is caused by Earth’s orbit around our Sun. In the summer, viewers are looking in a different direction in space at night than they are during the winter. • How many: • There are 13 astronomical zodiac constellations: Capricornus, Aquarius, Pisces, Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius, Sagittarius, and Ophiuchus. The annual cycle of the zodiac was used by ancient cultures to determine the time of year. • Why Don’t the Constellations Line Up with the Astrological Dates? • Were identified and connected to the calendar about 2500 years ago. • Earth’s seasons has shifted (Earth wobbles a little like a top) , making its axes point in different directions at different times. • Through time, then, the seasons have shifted with respect to the background of the zodiac constellations. • Five thousand years ago, our Sun passed through Taurus during the spring equinox; today it is in Pisces at the start of spring.
