ASTRONOMY 5



ASTRONOMY 5

Lecture 1 Summary

INTRODUCTION TO COSMOLOGY

1) The Universe:

• Intergalactic space is big, dark, and empty.

• In it are galaxies, about 100,000 light years across and 5 million light years apart.

• Galaxies are big piles of stars (100 billion or so) and many rotate slowly, like giant pinwheels.

• Our Milky Way is such a galaxy. We live in its “suburbs.”

• Galaxies stretch away in space as far as giant telescopes can see.

2) The whole space filled with galaxies is getting bigger. The galaxies are flying apart rapidly…the Universe is EXPANDING.

3) Units of time are different from units of distance…some examples:

Time: Year The Universe is 10-20 billion years old.

Distance: Light year The distance light travels in one year.

6 trillion miles = 1016 meters.

Nearest star is 4 light years away.

Distance: Parsec Approx. 3 light years.

20 trillion miles = 3 x 1016 meters.

The parsec is the astronomer’s favorite way of expressing distance. We will use both light years and parsecs.

4) Powers of 10: Count the zeroes

1,000,000,000,000 Trillion 1012 Exponent = the

1,000,000,000 Billion 109 number of zeroes

1,000,000 Million 106 up here

1,000 Thousand 103

100 Hundred 102

10 Ten 101

1 One 100 Exponent = 0!

.1 = 1/10 Tenth 10-1

.01 = 1/100 Hundredth 10-2

.001 = 1/1000 Thousandth 10-3

1/1,000,000 Millionth 10-6 Exponent = -1 times

1/1,000,000,000 Billionth 10-9 the number of zeroes

1/1,000,000,000,000 Trillionth 10-12 in fraction down here

To multiply powers of ten, add the exponents. To divide powers of ten, subtract the exponents.

General example: 3000 x 0.04 = 3 x 103 x 4 x 10-2 = 12 x 101 = 1.2 x 102

5) Solar System model: A one trillionth-scale model of the Solar System fits nicely into a living room, with the Sun as a 100 watt light bulb. The nearest star is another such light bulb 25 miles away. The Galaxy is 100 billion such light bulbs spread out into a disk within the orbit of the Moon, with a thickness equal to the Earth’s diameter (to visualize 100 billion: a big shopping bag holds about 1 million grains orf rice. 100 billion rice grains therefore takes100,000 shopping bags---if stacked side by side these would make a line 25 miles long). The edge of the visible Universe in this model is 1/30th the distance to the nearest star.

Scary thought: the world population is 6.5 billion, which is 6500 shopping bags

of rice. We have big numbers in our own backyard!

6) Another model: If the Sun is an orange in New York, the nearest star is another orange in Chicago. The Galaxy fits into the space between the Earth and the Sun.

7) Still a third model: If the Sun and its nearest neighbor star are 2 mm apart, the Galaxy is the size of a football field.

The Galaxy is very empty…and the space between the galaxies is even emptier.

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download