Astronomy 170: Aug am class Turn in HW 1 in the front of the room. If you didn’t get HW 1 on Monday, turn it in on Friday. If you didn’t get the telescope lab on Monday, pick it up from Johanna. If you weren’t in class on Monday and need all 3 handouts, get them from Johanna. Turn in HW 1 on Friday. If you didn’t get the honors section instructions, get them from Megan. We increased the enrollment limit for the honors section, Section 3. If you are in Section 2 and want honors credit for this class, you must fill out a change of section form and have Prof. Bechtold sign it.

Back to our COSMIC ADDRESS Steward Observatory, The University of Arizona Tucson, Arizona United States, North America Earth Solar System Milky Way Galaxy: The Sun is one star of many in the Milky Way The Milky Way as seen from Earth

Spiral Galaxy

Our Milky Way, Plus many “dwarf” satellite galaxies

The LOCAL GROUP

The Andromeda Galaxy The other big spiral galaxy in the Local Group About 2.5 million Light years from The Milky Way

The Local Group is on the edge of the VIRGO CLUSTER OF GALAXIES

A photograph of the center of the VIRGO CLUSTER OF GALAXIES

SUPER- CLUSTERS

OUR COSMIC ADDRESS Steward Observatory, The University of Arizona Tucson, Arizona United States, North America Earth Solar System Milky Way Galaxy Local Group of Galaxies Virgo Cluster of Galaxies Local Supercluster of Galaxies The UNIVERSE Summary

Patterns in the Sky: Descriptive Astronomy Astronomy: From the Greek astronomos astron = star nomos = a system of laws Astronomy: From the Greek astronomos astron = star nomos = a system of laws Astronomy is one of the oldest sciences The earliest humans studied the night sky and the motion of the stars and planets

Constellations There are about 6000 stars visible to the naked eye on a clear, moonless night at a dark site People like to see patterns: Constellations are patterns in the stars that look like people, everyday objects, animals Earliest records of constellations date to 3000 BC Modern astronomers have divided the sky into 88 constellations

Example: Orion, the Hunter

The Big Dipper; Polaris (the North Star)

Constellations are just apparent patterns on the sky The stars in a particular constellation may or may not be physically near each other in space Most often the stars in a constellation are at very different distances from Earth From a different star in the Milky Way, constellations would be different.

The Celestial Sphere

Why define constellations? Story-telling mneumonics Religious and ritual meanings Navigational aids Phoenicians, Pacific Islanders used constellations to sail great distances Watch constellations move as Earth rotates  define time, calendars

Motion of Stars in the Sky Key Facts and Concepts: The Earth ROTATES on its axis once every 24 hours The Earth REVOLVES around the Sun once a year The Earth’s rotation is counterclockwise looking down on the North Pole and thus the Sun and stars appear to RISE in the East and SET in the West.

The orbital path of the Earth around the Sun is called the ECLIPTIC. The Earth’s axis of rotation is tilted 23 ½ degrees with respect to the ecliptic plane.

The orbit of the Earth around the Sun is not a circle; it is an ellipse

Longitude and Latitude Longitude and latitude define your position on Earth. The zero of latitude is the Equator The zero of longitude is the prime meridian: line which passes through the old Greenwich observatory outside London, England. Tucson: Latitude 32 degrees North, Longitude: 110 degrees west