AS101 LESSON 1

Astronomy is a global effort

Studied worldwide through international cooperation and shared data

Scientific method

Observe, test ideas, revise using evidence

Scientific notation

Writing very large or small numbers using powers of 10

Astronomical Unit (AU)

Average distance from Earth to Sun

1 AU

About 150 million km

Light-year

Distance light travels in one year

Why use AU and light-years

Space distances are too large for km units

Universe

Everything that exists: matter, energy, space, and time

Age of universe

About 13.8 billion years

Big Bang

Event that began the universe

Solar system

Sun and all objects orbiting it

Galaxy

Large collection of stars, gas, and dust held by gravity

Milky Way Galaxy

Galaxy containing our solar system

Local Group

Cluster of nearby galaxies including Milky Way

Supercluster

Group of galaxy clusters

Cosmic Calendar

Universe history compressed into one calendar year

Big Bang on Cosmic Calendar

January 1 at midnight

Solar system formed on Cosmic Calendar

Mid-August

Primitive life on Earth on Cosmic Calendar

End of September

Dinosaurs on Cosmic Calendar

Late December

Recorded human history on Cosmic Calendar

Final seconds of December 31

Constellation

Recognizable pattern of stars in sky

Why constellations are not real groups

Stars are at different distances from Earth

How many stars visible naked eye

Up to about 3,000 on dark clear night

Celestial sphere

Imaginary sphere surrounding Earth used to map sky

Zenith

Point directly overhead

Horizon

Boundary between Earth and sky

Daily sky motion appears

East to west because Earth rotates west to east

Night sky changes with seasons

Earth orbits the Sun