Key Topics

Astronomy Unit

Big Bang Theory: most widely accepted theory for the origin of our universe.• States that 12-14 billion years ago, the universe was only a few millimeters across.• According to this theory, the contents of the universe expanded explosively into existence about 13.7 billion years ago. • After the big bang, the universe expanded quickly, and continues to expand, and cooled enough for atoms to form. •Gravity pulled the atoms together into gas clouds that eventually became stars, which comprise young galaxies.

History of the Universe

1. Galaxies appear to be moving away from us at speeds proportional to their distance. • This is called Hubble’s Law, named after Edwin

Hubble who discovered this phenomenon in 1929. This supports the expansion of the universe and suggests that it was once compacted.

2. If the universe was initially very hot as the big bang suggests, there should be remnants of this radiation. • In 1965, Radioastronomers Arno Penzias and

Robert Wilson discovered Cosmic Background Radiation, which supports the Big Bang.

3. The abundance of “light elements” Hydrogen and Helium found in the universe is thought to support the Big Bang.

Evidence of Big Bang Theory

Technology provides the basis for many new discoveries related to space and the universe.

• Visual, radio, and x-ray telescopes collect info from across the entire electromagnetic spectrum.

• Computers are used to manage data and complicated computations.

• Space probes send back data and materials from remote parts of the solar system.

• Accelerators provide subatomic particle energies that simulate conditions in the stars and in the early history of the universe before stars formed.

Technology and the Universe

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=kfoMufdG6hOBFM&tbnid=nHkyTUBDjH5jCM:&ved=0CAUQjRw&url=http://www.space.com/10691-oldest-galaxy-discovered-hubble-space-telescope.html&ei=NXmsUpKlNKPhygHj44GIAw&psig=AFQjCNGqbZ2oMIYUyNkTC8NWVkfMEy3Yjw&ust=1387121162866997

A galaxy is a group of billions of individual stars, star systems, star clusters, dust and gas bound together by gravity. There are billions of galaxies in the universe, and they are classified by size and shape. They vary in size from a few thousand to a hundred thousand light years across.

What is a Galaxy?

A spiral galaxy

1.Elliptical Galaxies: round or oval in shape; some of the largest galaxies are elliptical galaxies. They are thought to be the most common type of galaxy in the nearby universe.

3 Types of Galaxies

Elliptical Galaxy M87

2.Spiral Galaxies: disc shaped galaxy that has a bulge in the middle; have spiral arms; makes up more than 50% of galaxies

3 Types of Galaxies (continued)

Spiral Arm: contains gas and dust clouds and mainly hot, young stars

Central bulge is packed with old red and yellow stars, which glow the brightest

3.Irregular Galaxies: cannot be classified as elliptical or spiral; makes up about 3% of galaxies.

3 Types of Galaxies (continued)

Irregular Galaxy

• Our solar system is part of the Milky Way Galaxy, which is a spiral galaxy.

• It has more than 100 billion stars and a diameter of more than 100,000 light years.

• At the center is a bulge of stars from which are spiral arms of gas, dust, and most young stars.

Our Galaxy; The Milky Way

• Hubble’s Law states that galaxies which are farther away have a greater red shift, so the speed at which a galaxy is moving away is proportional to its distance from the Earth.

Hubble’s Law

• The red shift is a phenomenon due to Doppler shifting, so the shift of light from a galaxy to the red end of the spectrum indicates that the galaxy is moving farther away. • This is evidence for the Big Bang

Theory because it tells us that the universe is still expanding.

• http://wosu.pbslearningmedia.org/resource/phy03.sci.phys.fund.hubble2/hubbles-expanding-universe/

Hubble’s Law and the Red Shift

• Early in the formation of the universe, stars coalesced out of clouds of hydrogen and helium and clumped together by gravitational attraction into galaxies.

Stars

• When heated to a sufficiently high temperature by gravitational attraction, stars begin nuclear fusion, which converts matter to energy and fuse lighter elements into heavier ones.

• All of the elements, except for hydrogen and helium, originated from the nuclear fusion reactions of stars.

Stars

• Stars are classified by:• Color : from hottest to coldest: • O (blue), B (blue), A (blue), F (blue to

white), G (white to yellow), K (orange to red), M (red)

• Size• Luminosity: amount of energy released

from the star; measured in Watts• Mass

Classification of Stars

• A star’s mass determines the star’s place on the main sequence and how long it will stay there.

• Patterns of stellar evolution are based on the mass of the star.

• Stars begin to collapse as the core energy dissipates.

• Nuclear reactions outside the core cause expansion of the star, eventually leading to the collapse of the star.

Stars

• A Hertzprung-Russell diagram is used to estimate the sizes of stars and predict how stars will evolve.

• Most stars fall on the main sequence of the H-R diagram, a diagonal band running from the bright hot stars on the upper left to the dim cool stars on the lower right.

Hertzsprung-Russell Diagram

Hertzprung-Russell Diagram