So.......let the course begin!

What do we see if we watch the sky?

Key points: relative scales from atoms to the Universe; scientific notation

## The Scale of Astronomical Studies

Astronomers need to be familiar with how matter and light behave on a vast range of size scales.

Below is a quick tour of the range of size scales included in the study of astronomy. It starts with the "frothy" organization of galaxies in the Universe, zooms in to the Milky Way, then through star clouds to pick out the sun. As it zooms in further, it identifies the planetary system, to the inner planets, to the earth and moon, and then the earth alone where it comes down in Switzerland to a flowering bush. It continues to zoom through a fly on the bush to the DNA in the eye of the fly. Inside the DNA it travels through the cloud of electrons surrounding a single carbon atom, to the atomic nucleus and finally isolates a single proton with its internal quarks.

 To deal with this immense range of scales, we use scientific notation, where the size of the number is given as a power of ten and its value as a leading decimal number with the parts connected by "x" for "times." For examples, see the two bullets below. This animation expands the magnification about ten times in each transition to show how much the view changes! The frame size goes from 1025 m to 10-15m.  (Adapted by G. Rieke, from http://cern.web.cern.ch/CERN/Microcosm/P10/english/welcome.html with supplements from the Eames Powers of Ten series and others)
• the atomic nucleus is the fundamental unit of matter; a typical atomic nucleus is 0.0000000000001 meters in diameter, which is 1.0 x 10-12 meters in scientific notation.
• the typical distance from one star to the next in the Milky Way galaxy is 37,840,000,000,000,000,000 meters which is 3.784 x 1019 meters in scientific notation.

To relive the "Powers of Ten" movie, go to http://scaleofuniverse.com/. You can select the original, or a more quirky one "The Scale of the Universe." It is curious that the sequence of transitions has a certain similarity between the large and small scales - orbits around the sun, or around the atomic nucleus for example

And here is a far more artistic version from the American Museum of Natural History Caution!! Large file. Do not attempt with low bandwidth connections!!

For practice on scientific notation, or check out:

http://janus.astro.umd.edu/astro/scinote/

How do these scales work out in practical terms?

We can make a model of our surroundings in the form of an orange for the sun at the front of the lecture hall, a grain of salt representing the earth in the front row, and a peanut representing Jupiter in the back row. The next nearest star is represented by another orange -- in Dallas!

 Bringing the monster to life, from "Young Frankenstein," Mel Brooks Star petroglyphs, in "Planetarium Cave," Canyon de Chelly, from Gary Tepfer, http://www.wlotus.com/GaryTepfer/default.htm Click to return to syllabus Click to go to Scientific Method hypertext G. H. Rieke Click to go to Appearance of the Sky