2 C1 S2 Stars

Stars Seeing the Universe Section 2

Constellations • Early Greeks and Romans observed patterns in the sky and named them after mythological characters and animals – Today, we divide the sky into 88 constellations – They rotate around Polaris (the North Star) • Polaris is directly above the north pole.

Which is the Brightest? • Brightness is measured in magnitude – Absolute magnitude is the measure of how much light a star gives off • This depends on size and temperature

– Apparent magnitude is how bright the star appears to us on Earth • This depends on size, temperature, and distance from the Earth

Which is the Brightest? • For example – Sirius (Canis Major: The Dog) is a much brighter star than Rigel (Orion: The Hunter) – Sirius appears brighter because it’s actually 100 times closer to the Earth than Rigel – If they were the same distance, Rigel would be much brighter

What is a Parallax? • Try holding your thumb half a foot from your face and look first with your left eye, then your right. – Note how far your thumb switches back and forth

• Now try again with your arm all the way extended – Does your thumb shift more or less?

What is a Parallax? • The apparent shift in position is called a parallax. • Scientists use a star’s parallax to measure its distance from the Earth. – We won’t look at the actual math behind these measurements, its not sixth grade material. – Let’s visualize what all this means

Properties of Stars • The color of a star indicates its temperature – Hot stars are blue-white in color – Cool stars look orange or red – Stars about the same color of the Sun are yellow

More Properties of Stars • How can we know what stars are made of? – Scientists study the star’s light through a tool called a spectroscope – The spectroscope spreads light out like a prism – Elements in the star’s atmosphere show up as dark lines on the spectroscope

Light being bent by a prism

Vega

The Sun

How do Stars Shine? • Last chapter, we said that Einstein established the relationship between mass and energy with his equation E=mc2 – “E” is energy and “m” is mass – In the last century, scientists determined that stars released HUGE amounts of energy by slamming hydrogen atoms together

How do Stars Shine? • This reaction is called fusion. – The basic fusion reaction is 4 hydrogen atoms combine to form 1 helium atom – 1 helium atom has a little less mass than 4 hydrogen atoms…so where did that mass go? • Like Einstein said, it was converted into energy • This energy is what causes stars to shine! • Lets look at a diagram

Don’t worry about words like positron and neutrino. Just look at protons and neutrons

Life Cycle of a Star • This link goes to a webpage that gives us an idea of how stars are born and die – As we look at the animations in class, take notes in the margin on the power point handouts. • • • • • •

Can you define these words? Nebula Red giant/supergiant White dwarf Neutron star Black hole