Download Astronomy 170: Aug. 24 10am class

Astronomy 170:
Aug. 24 -- 10am 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
SUPERCLUSTERS
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 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