Lecture 29 – An advertisement: two astronomy courses next semester

• 29:52 ,“Characteristics and Origins of the Solar System, 1:30 – 2:20 MWF

• 143:070:001, Honors Seminar in Natural Sciences, “Life in the Universe: Scientific Bases for Speculation”, 2:30-3:45 TTh

Why study the solar system next semester?

Jupiter, Saturn, and Venus will all be

in the evening sky

Astronomical Events this Month

• Venus in the western sky after sunset

• Total eclipse of the Moon, November 8 (Saturday night) 5:32 PM 7:06 7:31 9:04

• Leonid meteor shower, November 18, before dawn

Last word on massive stellar evolution: it happens fast and

ends violently

Eta Carinae: Watch the skies! Watch the skies!

Next topic: Structure of the Milky Way Galaxy

What is the size, shape, and nature of the system of stars in which we live?

You can learn a lot by looking at the sky and thinking

From this picture, let’s figure out the shape of the Milky Way. Characteristics to go on are:

• Sprinkling of stars everywhere

• Thick band of light across the sky (the Milky Way)

• Band brightest in the direction of Sagittarius

• Band faintest in the direction of Taurus-Auriga

What’s the answer?

The Answer

How far is it to the galactic center?

How could we know?

Hint provided by globular star clusters. Great summertime objects, few in winter

How globulars indicate the distance to the galactic center

Globular Clusters are Distant

It must be a long way to the galactic center

Globular cluster Distance (light years)

M13 (Hercules) 21,000

M15 (Aquarius) 34,000

M92 (Hercules) 26,000

M4 (Scorpius) 14,000

M5 (Serpens) 26,000