Unit Tools of Astronomers Telescopes make faraway objects seem closer.

Two types of telescopes Refracting telescopes use lenses to gather light. Reflecting telescopes use mirrors to gather light.

Unit

Other types of telescopes Radio telescopes – (on Earth) produces images by picking up radio waves from space Infrared telescopes – (on satellites) produces images by looking at infrared waves X-ray telescopes – (on satellites) detect high energy radiation from space

Key Question: How does a telescope work?

Magnification – measure of the number of times the image being viewed is enlarged. Magnification is equal to the focal length of the objective lens divided by the focal length of the eyepiece.

Parallax is the apparent change in position of an object when you look at it from different directions. To use parallax, astronomers determine the position of a star in the sky relative to other stars that are too far away to show movement. Using geometry, they can determine the distance of the star from Earth. Parallax is used for distances less than 1000 light years.

The apparent brightness of an object depends on how far away it is and how much light it actually gives off (its absolute brightness). The mathematical relationship between these variables is known as the inverse square law and is used to determine the distance to stars and galaxies over 1000 light years. The inverse square law shows how the apparent brightness of an object decreases as you move away from it.

Comparing parallax and inverse square law ParallaxInverse Square Law How far?For measuring distances less than 1000 light years For measuring distances more than 1000 light years How do they do it? Uses the stars relative position to background stars Uses the apparent brightness of stars

Unit The Inverse Square Law

Unit The Inverse Square Law

What does it mean? The Inverse Square law states: Doubling the distance between the light and the subject results in one quarter of the light hitting the subject.

Astronomers infer values for absolute brightness using a source of light called a standard candle. A standard candle is an object, such as a star, whose absolute brightness is known.

A second type of standard candle is called a Cepheid star. This type of star was discovered by Henrietta Leavitt ( ), an American, in the early 1900s. Leavitt discovered that there is a relationship between the pulsing of Cepheid star and its absolute brightness.

1. This type of telescope uses mirrors to gather light. A. Reflecting B. Refracting C. Radio D. infrared

2. This type of telescope uses lenses to gather light. A. Reflecting B. Refracting C. Radio D. infrared

3. This is the measure of the # of times the image being viewed is enlarged A. 100x B. Parallax C. Magnification D. enlargement

4. What form of math do astronomers use when using parallax to determine how far away a star is? A. Algebra B. Calculus C. Geometry D. Physics

5. As the distance of an object increases the apparent brightness _________. A. Increases B. Decreases C. Stays the same D. disappears

6. According to Inverse Square Law, if you double the distance TWICE between an object only ___ of the light will be able to be seen at that distance A. ½ B. ¼ C. 1/8 D. 1/16

7. When a star’s absolute brightness is known it is called: A. A bright sparkle B. A super giant C. A brown dwarf D. A standard candle

8. _____ uses the stars relative position to other stars to determine their distance away from earth. A. Inverse square law B. Standard candle C. Cepheid star D. parallax

9. ____ brightness means at the same distance one object may appear brighter than another object because of the actual light amount. A. Apparent B. Absolute C. Awesome D. Total

10. Leavitt discovered that there is a relationship between the pulsing of a ______ and it’s absolute brightness. A. Quasar B. Brown dwarf C. Standard candle D. Cepheid star