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 - 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!

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 & energyVideo (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

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

Telescope Altitude Adjustment Gauge

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 longVideo (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 reversedVideo (6:00) “Mechanisms of the Seasons”

Classwork Assignment