Chapter 1:Why Learn Astronomy?

We Have Studied Astronomy Since Ancient

Times

Astronomy is the oldest science. Every ancient culture studied motions in the sky

Compared to the universe, the Earth is less than a grain

of sand on a beach

Watch YouTube Size Comparison and Journey to the Big Bang WMAP videos

Our Cosmic Address

We believe that superclusters are the largest structures to have formed thus far in the universe. Will something larger form in the far future? Probably not but we can’t say for sure.

Light travels at a finite speed: about 300,000

kilometers/second

Watch One Small Step HD video

Because of the finite speed of light, we can see back in

time

WMAP image of the Cosmic Background Radiation. Light from the edge of the visible

universe.

Play with Look Back Simulator in ClassAction Introductory Concepts

module

Astronomers use the

Scientific Method to

gain an understanding

of the Universe

Astronomers study the “patterns among the stars”

In order to make sense of what we see we need a Cosmological Principal

Mathematics is the language of Astronomy and Physics

Pythagoras569 – 475BC“The underlyingStructure of theUniverse isMathematical”

Isaac Newton 1642 – 1727 Newton invented

calculus to explain his mechanical

universe. The orbits of the planets were like the hands

on a giant clock

Albert Einstein 1879 – 1955According to

Einstein, the Universe is a much stranger place than Newton thought. Newton could never have imagined black holes but Einstein’s theories predict them.

Dealing with numbers large and small

Scientific Notation

4,500,000,000,000,000 = 4.5x1015

0.000000000000000028 = 2.8x10-17

Common Prefixescenti = 0.01 = 10-2 (c)milli = 0.001 = 10-3 (m)nano = 0.000000001 = 10-9 (n)kilo = 1,000 = 103 (k)mega = 1,000,000 = 106 (M)giga = 1,000,000,000 = 109 (G)

Range of numbers we deal with in astronomy

DistancesAround the Earth…meters (m) or kilometer (km) 1 m ≈ 39.37 inches 1 km = 1000 m = 0.621 miles

Around the Solar System…AU 1 AU = Average Earth – Sun distance 1 AU = 1.496x1011 m = 149.6 million km

Beyond the Solar SystemLightyear (ly)

1 ly = distance light travels in 1 year 1 ly = 9.46x1015 m = 9.46 trillion km

Parsec (pc): distance at which an object shows a

parallax of 1 arcsecond: 1pc = 3.26 ly= 30.84 trillion

km

Other UnitsMass…kilograms (kg)

1 kg = 1000 grams1 kg = 2.205 lbs*

*(a pound is not really a mass, it is a force. In the US, we tend to use it like a mass, though)

Time…Years, Days, Hours, Minutesand Seconds

Temperature…°C°C = (°F - 32°) x 5/9

also use Kelvin scale°K = °C + 273°