Astronomy 1020 Stellar Astronomy Spring_2015 Day-2

 Modern astronomy is more than cataloging objects.  How do stars (matter and energy) work?  What is the universe?  How do humans fit in?

 Earth is a small planet,  orbiting a medium- sized star,  in a galaxy of 100 billion stars,  which is just one of billions of galaxies,  in a universe that is 13.7 billion years old.

 The universe is vast.  Billions of galaxies are separated by thousands of trillions of miles.  Astronomers need to be able to talk about great distances.

 Use the travel time of light to measure distances.  We often use times to denote distances.  For example, we may say a friend’s house is two hours away.  Compare distances by the amount of time it takes to travel them.

 Light travels 300,000 km every second.  Universe’s greatest speed.  Light-year: distance light travels in one year.  Light could travel around Earth in 1/7 second.

Light Travel Times  Light takes: 1¼ seconds to arrive from the Moon. 8.3 minutes to arrive from the Sun. 5.5 hours to get to Pluto from the Sun.

 Light takes: 4.2 years to arrive from the nearest star. 100,000 years to cross the galaxy. 2.5 million years to get to the nearest big galaxy. 10 billion years to come from distant galaxies.

 Studying the universe can reveal many things.  For example, except for the hydrogen in water (H 2 O), all the atoms in our body were made in stars.  Stars generate energy by making heavier elements out of light ones.

 Dying stars eject those elements into space in massive explosions.  New stars and planets (and humans) form.  We are stardust, made from the materials provided by earlier generations of stars.

 Test scientific ideas by observation.  Space exploration has expanded our view of planets and the Solar System.  Telescopes, satellites, etc., extend it more.

 Science involves the use of theories, hypotheses, and principles.  A scientific hypothesis s an idea that leads to testable or falsifiable predictions.  The cosmological principle is a very important underlying assumption: “There is nothing special about our place in the universe.”

 Cosmological principle on one level: Our view from the Earth is not special or unique. Distant objects should be like nearby ones, which we can study in detail.  On another level: Matter and energy obey the same physical laws everywhere. We can learn about distant objects by studying nearby ones.

Homework! By Monday (assuming it is clear), go outside and look at the sky. Make a note of your location, look angle & time. Do it again at least 1 or more hours later. A sketch may help. Are there any changes?

How to Attack the course Read the text – preferably BEFORE class. Visualize the concept. Quiz yourself (and others) Try to teach the material to your study group. Focus - Concepts, Relationships, Connections. Don’t psych yourself out over the “math”. Stay current with assignments. If you have questions … Office Hours!!!