Unit I - Lesson I “Foundations of Astronomy” 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

Solar System

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 quadrillion km or 100,000 light years in diameter  It would take a beam of light 100,000 years to cross the entire galaxy!

The Milky Way 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 SizeVideo (2:34) “Let’s Talk About Size” 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

Polaris

Polaris is Part of a Triple-Star System – Artist Concept

Constellations Celestial coordinates are used to locate specific stars & constellations on the sphere 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 Right Ascension (RA) – or “longitude” are the “up & down” lines in the sky Declination (dec) – or “latitude” are the “side to side” lines Declination (dec) – or “latitude” are the “side to side” lines

Constellations Azimuth - angle of horizontal deviation from north 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 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) Celestial coordinates uses hours, minutes & seconds (smaller units of degrees)

Constellations 360 o / 24 (hours in a day) = 15 o 360 o / 24 (hours in a day) = 15 o So 15 o = 1 hour So 15 o = 1 hour Altitude - ranges from 0 to 90 degrees, and measures the angle between the horizon; you and the object 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 Ex. an object with 0 degrees altitude is right on the horizon; while an object at 90 degrees altitude is directly overhead

Telescope Altitude Adjustment Gauge

Earth’s Motions Sidereal Day – takes into account that the Earth is also revolving around the Sun as it rotates 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 Solar Day – Earth spins once on it’s axis every 24 hours Sidereal day is only 23 hours & 56 minutes long Sidereal day is only 23 hours & 56 minutes long Video (0:42)Video (0:42) “Sidereal vs. Solar Day” “Sidereal vs. Solar Day Video (0:42)“Sidereal vs. Solar Day

Earth’s Motions  Earth takes 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)Video (6:00) “Mechanisms of the Seasons” “Mechanisms of the Seasons Video (6:00)“Mechanisms of the Seasons

Classwork Assignment