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Telescopes L1 Purpose of this Lab • Telescopes: See Use Understand L1 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 D2 • 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? L1 Sensitivity L1 What is the Purpose of a Telescope? 2. Increase the detail (resolution) we see. Resolution is inversely proportional to Telescope Diameter. = a constant times l/D Diffraction Limit If D increases then 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? L1 Resolution L1 Types of Telescopes L1 Refractor L1 optical Yerkes 40-inch refractor L1 Reflector L1 Hooker 100-inch reflector optical L1 Keck twin 10meter reflector optical/IR L1 Arecibo 300-foot reflector radio L1 Atmospheric Seeing L1 • Seeing degrades resolution • Adaptive optics can recover resolution • Engineering limits telescope size L1 Resolution and Seeing Neptune with the Palomar 200-inch reflector L1 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 500X magnification!” • But sensitivity ALWAYS increases with bigger telescopes. L1 Magnitude Scale • The SMALLER the number the BRIGHTER the star! • Every difference of 5 magnitudes is a 100X difference in BRIGHTNESS. • Every difference of 1 magnitude = 2.5X brightness L1 Magnitude vs. Brightness Mag. Difference 1 Factors of 2.5 2.51 = 2.5 Brightness Diff. 2.5 2 2.52 = 2.5 X 2.5 6.3 3 2.53 = 2.5 X 2.5 X 2.5 16 4 2.54 = 2.5 X 2.5 X 2.5 X 2.5 40 5 2.55 = 2.5 X 2.5 X 2.5 X 2.5 X 2.5 100 6 2.56 = 2.5 X 2.5 X 2.5 X 2.5 X 2.5 X 2.5 250 L1
