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Day Time Person Mon 10:00 – 11:00 PM Michelle Krok Mon 11:00 – 12:00 PM Jessica Fielder Tues 9:00 – 10:00AM Joey Fedrow Tues 2:00 – 3:00 PM Abby Fuller Thurs 12:00 – 1:00 PM Vanessa Bell Thurs 10:00 – 11:00 AM Joey Fedrow (in TH413) Thurs 9:50 – 10:40 AM Abby Fuller Thurs 1:00 – 2:00 PM Abby Fuller Thurs 1:00 – 2:00 PM Michelle Krok Fri 12:00 – 1:00 PM Jessica Fielder Fri 4:00 – 5:00 PM Chandra Vanajakshi Help Sessions in TH 411


Reading Chapter 1: The Scale of the Cosmos Chapter 2: The Sky


Overview The Birth of Astronomy Stars & Constellations Distances to Stars The Speed of Light

Ancient Observers: 

Ancient Observers Ancient humans observed the sky They noticed that the Sun rises every day in the eastern half of the sky and sets in the western half. The Moon also rises in the east and sets in the west The stars also rise in the east and set in the west. When they asked themselves “Why?”, astronomy was born.

Earth rotates on its axis once per day: 

Earth rotates on its axis once per day Today we understand that the Sun rises and sets due to the rotation of the Earth. The Earth rotates toward the East making the Sun appear to move West until it sets. The same is true for the Moon and Stars. Viewed from the North the Earth moves counter-clockwise.


Constellations In Ancient Times, people saw patterns in the stars. They named these constellations for things that were important to their culture. Different cultures saw different patterns Later, astronomers defined these constellations precisely, and still use them to identify parts of the sky. Note: The stars in a constellation are not near each other in space.


Centaurus, the Centaur & Scorpius, the Scorpion


Chinese Star chart (Actual photograph) Chart showing Greek hero Perseus


Orion, The Hunter (Actual photograph)


Orion (star chart) Stars were given names by ancient people They are also classified using Greek letters: a - Alpha, the first Greek letter, designates the brightest star in a constellation.

Ursa Major: The Great Bear (a.k.a. The Big Dipper): 

Ursa Major: The Great Bear (a.k.a. The Big Dipper)


The North Star is called Polaris, because it is at the North Celestial Pole. It is also called a Ursae Minoris. It is visible every night because it is above the North Pole of Earth. It is not a very bright star. Two stars in the big dipper point to Polaris, and can be used to find which way is North!

Rising and Setting Stars: 

Rising and Setting Stars The Earth’s eastward rotation causes stars to appear to move westward. Stars near the North Celestial Pole move in small circles Stars far from the pole move in long arcs Polaris, the North Star, moves the least of any.


The stars in a constellation are not close in space In fact, the stars slowly move through space. Many years from now, the constellations will look different!

Distances to Stars: 

Distances to Stars Stars were once thought to be fixed in a dome above the Earth. We now know that the stars are scattered through space at great distances. The nearest stars are located about 10 trillion miles away. (10,000,000,000,000 miles) Astronomers measure such distances using a unit: the light year

Light Years: 

Light Years Light can travel very fast: 3.0 x 108 m/s That’s 186,000 miles per second! Even at this speed, light takes a long time to travel between the stars The distance light can travel in 1 year is called Light Year. (1.y.) One Light Year = 1 x 1016 meters

Light Years: 

Light Years Light-Year is a unit of distance A light-second is the distance light travel in one second. The Sun is 8 light minutes away The nearest other stars are 3 light years away The nearest galaxy is 2 million light years away

Looking back in Time: 

Looking back in Time Although light travels fast, it does not move instantaneously For example it takes light from the star Rigel (in Orion) 800 years to reach us. So we see Rigel as it was 800 years ago. We see the Andromeda Galaxy as it was 2 million years ago.

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