Astronomy-the study of stars

Stars• Huge spheres of hot, glowing gas

– Example = sun

• Stars give off energy---how do we know this?

Energy = wavesElectromagnetic spectrum

• Huge spheres of hot, glowing gas– Example = sun

• Stars give off energy---how do we know this?– Visible light = we can see lots of stars in the

sky– Radiant energy from the sun heats the earth– Also, some stars give off radio waves

Telescopes

• Use lenses or mirrors to collect and focus light from distant objects

• Three different types:– Refracting telescope– Reflecting telescope– Radio telescope

Both of these are visible light telescopes

Refracting telescope

• Consists of 2 convex lenses– First lens (objective lens) gathers the light and

focuses it– Second lens (eyepiece lens) magnifies it

Reflecting Telescope

• Uses a concave mirror to gather and focus light

• A smaller mirror inside reflects this image to the eyepiece lens which magnifies it

Radio Telescope

• Detects radio waves given off by objects in space

• Most have curved reflecting surfaces that are several hundred meters in diameter

• The bigger the radio telescope, the more radio waves it can collect

Traits which are only true of reflecting telescopes

Traits which are only true of refracting telescopes

Traits which are only true of radio telescopes

Telescopes: Similarities and Differences

Spectroscopes

• Also called a spectrograph

– Breaks the light from an object into its color spectrum

– Astronomers use this to get information about stars including their chemical compositions and temperatures

Spectroscopes: star’s chemical composition

• What elements is a star made up of?

• Astronomers compare the banding patterns of known elements to those of the stars.

What elements does this star contain?

What makes up the universe?

• On the right side of your paper, list as many things as you can come up with in one minute.

• Stars, galaxies, star systems, nebulae, etc.

• Universe = space and everything in it!

Review: What is a star?

• A star is a huge sphere of hot, glowing gas.

• Can you think of any examples of stars? – The sun is a star!

Stars

• What pieces of equipment can be used to gain information about stars?– Reflecting telescope– Refracting telescope– Radio telescope– SPECTROSCOPE!!

What is a galaxy?

• A galaxy is a cluster of stars.

• Billions of stars make up a galaxy.

Can you think of the name of our galaxy?– Milky Way galaxy

How do we measure distance to stars and other galaxies?

• We have to use a unit called a light year.

• A light year is the distance light can travel in one year….HUGE!

• light year is a unit of distance, not time!!!!

• 1 light year= ~9.5 million million kilometers

Parallax

• Parallax is the apparent change in position of an object when you look at it from different places.

What characteristics classify stars?

• All stars are huge spheres of glowing gas (mostly hydrogen).

• Stars are classified based on 3 main physical characteristics:– Temperature– Brightness– size

LAB: Color vs. Temperature

• You will record the data for your lab in your Cornell notes on the RIGHT side.

Summary of Lab Findings

• On the right side, place the order of star color by increasing temperature

For example:

Coolest colornext colordsfsjsdhfjkhottest color

Temperature of stars

• Color of a star reveals its temperature.

• Remember the color vs. temperature lab?– Red stars = relatively cool stars (still hot

~3200 degrees Celsius)– Yellow- white = medium temperature (~5500

degrees Celsius)– Blue-white stars = hottest stars (>10,000

degrees Celsius)

Brightness of stars

• Brightness = the amount of light stars give off– This depends on its size and temperature– How bright it looks from Earth depends on

distance and actual brightness• Apparent magnitude• Absolute magnitude

Apparent Magnitude

• Brightness as seen from Earth

• Example: the sun looks very bright to us on Earth, but it is not the brightest star– It looks brighter because it is closer to earth

than other stars.

Absolute Magnitude

• Brightness of a star if it were a standard distance from the earth

Review

• What characteristics are used to classify stars?

• Now, we will look at graphs that show these characteristics of stars…they are called HR diagrams

Hertzsprung – Russell Diagram