Telescopes L 1 Purpose of this Lab Telescopes

Telescopes L 1

Purpose of this Lab • Telescopes: See Use Understand L 1

What is the Purpose of a Telescope? 1. Increase the amount of light we see. Sensitivity is proportional to Collecting Area. S = a constant times p(D/2)2 If D increases, then S increases by D 2 • If your telescope is 3 times bigger than mine, then your telescope can see 32 = 9 times fainter objects than mine. • Can you read a book at night? What’s the faintest star you can see with your naked eye? L 1

Sensitivity L 1

What is the Purpose of a Telescope? 2. Increase the detail (resolution) we see. Resolution is inversely proportional to Telescope Diameter. q = a constant times l/D Diffraction Limit If D increases then q decreases by the same amount. • If your telescope is 3 times bigger than mine then you can see 3 times smaller angles (3 times smaller objects or detail). • Can you read a street sign a block away? Can you see the binary star in the Big Dipper with your naked eye? L 1

Resolution L 1

Types of Telescopes L 1

Refractor L 1

optical Yerkes 40 -inch refractor L 1

Reflector L 1

Hooker 100 -inch reflector optical L 1

Keck twin 10 meter reflector optical/IR L 1

Arecibo 300 -foot reflector radio L 1

Atmospheric Seeing L 1

• Seeing degrades resolution • Adaptive optics can recover resolution • Engineering limits telescope size L 1

Resolution and Seeing Neptune with the Palomar 200 -inch reflector L 1

Seeing and Magnification • Larger than a few inches, a telescope’s resolution stops getting better due to seeing. • Don’t be fooled by advertisements claiming huge magnification increases! – “Amazing 500 X magnification!” • But sensitivity ALWAYS increases with bigger telescopes. L 1

Magnitude Scale • The SMALLER the number the BRIGHTER the star! • Every difference of 5 magnitudes is a 100 X difference in BRIGHTNESS. • Every difference of 1 magnitude = 2. 5 X brightness L 1

Magnitude vs. Brightness Mag. Difference Factors of 2. 5 Brightness Diff. 1 2. 51 = 2. 5 2 2. 52 = 2. 5 X 2. 5 6. 3 3 2. 53 = 2. 5 X 2. 5 16 4 2. 54 = 2. 5 X 2. 5 40 5 2. 55 = 2. 5 X 2. 5 100 6 2. 56 = 2. 5 X 2. 5 250 L 1