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Astronomy. Unit I - Lesson I “Foundations of Astronomy ”. S.W.B.A.T. (Students Will Be Able To...). Identify our place in space Understand relative sizes of objects in space and discuss constellations Explain the celestial sphere and how objects are located in space
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Astronomy Unit I - Lesson I “Foundations of Astronomy”
S.W.B.A.T. (Students Will Be Able To...) • Identify our place in space • Understand relative sizes of objects in space and discuss constellations • Explain the celestial sphere and how objects are located in space • Discuss how time is measured; precession & the seasons
Our Place in Space • Earth: (small) 15 thousand km (12,000 miles) in diameter • Sun: 15 million km in diameter • Solar System: about 6 billion km in diameter
Our Place in Space • Light year – distance that light travels in one year or about 6 trillion miles (10 trillion km) • Local Stellar Neighborhood- 10 light years in diameter or about 60 trillion miles (90 trillion km)
Our Place in Space • Milky Way Galaxy- 1000 quadrillion km or 100,000 light years in diameter • It would take a beam of light 100,000 years to cross the entire galaxy!
Our Place in Space • Local Group-10 million light years in diameter • Includes 35 galaxies with the Milky Way & Andromeda the largest members
Our Place in Space • Astronomy – study of the universe • Universe - billions of galaxies (100?) • Includes everything that exists - all space, time, matter & energy • Video (2:34) “Let’s Talk About Size”
Hubble Space Telescope (HST) Deep-Field Camera Photo – Every Dot or “Smudge” is a Galaxy!
Constellations • Patterns of stars in the night sky • Named after mythological beings, heroes or animals • 88 constellations (mostly Greek) are recognized in the Western world • Different cultures grouped stars differently
Constellations • Ecliptic – plane in which the Sun & planets travel • Zodiac – 12 major constellations in the ecliptic
Constellations • Astrology (not a science) uses relative positions of stars and planets to attempt to predict the future • Astronomy & astrology were once the same in the distant past
Constellations • Celestial Sphere – model of stars & constellations that rotate around an unmoving Earth • Polaris (or the “North Star”) does not move • All other stars move around Polaris in circles due to Earth’s rotation
Constellations • Celestial coordinates are used to locate specific stars & constellations on the sphere • Right Ascension (RA) – or “longitude” are the “up & down” lines in the sky • Declination (dec) – or “latitude” are the “side to side” lines
Constellations • Azimuth - angle of horizontal deviation from north • Ex. exact North = 0°, exact East = 90°, exact South = 180°, exact West = 270°, exact North = 360° (or 0°)when using a compass • Celestial coordinates uses hours, minutes & seconds (smaller units of degrees)
Constellations • 360o / 24 (hours in a day) = 15o • So 15o = 1 hour • Altitude - ranges from 0 to 90 degrees, and measures the angle between the horizon; you and the object • Ex. an object with 0 degrees altitude is right on the horizon; while an object at 90 degrees altitude is directly overhead
Earth’s Motions • Sidereal Day – takes into account that the Earth is also revolving around the Sun as it rotates • Solar Day – Earth spins once on it’s axis every 24 hours • Sidereal day is only 23 hours & 56 minutes long • Video (0:42)“Sidereal vs. Solar Day”
Earth’s Motions • Earth takes 365.24 days to revolve around the Sun • Solstices – farthest north & south that the Sun appears in the sky • Equinoxes – when the Sun appears directly over the equator (equal day & night)
Earth’s Motions • Earth’s 23.5 degree tilt along with its orbit around the Sun is the cause of seasons
Earth’s Motions • Precession – Earth gyrates like a spinning top (cycle of 26,000 years) • Caused by gravitational forces from the Sun & Moon • In 11,000 years the seasons will be reversed • Video (6:00)“Mechanisms of the Seasons”
