Basic Instrumentation

Transcription

1 Basic Instrumentation Lecture 4: Telescopes & light Professor Kenny L. Tapp Astronomers rely on instruments that collect, magnify, and/or disperse light. The amount of light that can be collected is determined by the aperture of the instrument. A combination of lenses or mirrors focus light onto a detector. Detectors include photographic plates, photo-sensitive resistors. Telescopes have changed our understanding of the universe 27 Shapley observes dense star clusters... Location of the Sun in the Galaxy? Harlow Shapley Henrietta Leavitt Mount Wilson 60-inch Reflector Telescope (completed in 1914) Courtesy of Gale Gant Globular Cluster M13 Courtesy of Glenn Spiegelman 20 Galaxy image credit: Hugo, Gaul, Block (KPNO Visitor Program), NOAO, AURA, NSF - Globular cluster locations simulated If the Sun and planets were at the center, globular clusters would be evenly distributed around us. What did Shapley discover? 21

2 Location of the Sun in the Galaxy established! Galaxy image credit: Hugo, Gaul, Block (KPNO Visitor Program), NOAO, AURA, NSF - Globular cluster locations simulated Globular clusters are distributed to one side of us. The Solar System is nearer the edge of the Galaxy! Earth at Night Telescopes: Key Concepts (1) Telescopes use either a lens or a mirror to gather light. (2) The main purposes of a telescope are to gather light and resolve detail. (3) Radio and microwave telescopes use a reflecting dish to focus waves. (4) Telescopes in orbit avoid the distorting effects of the atmosphere. (5) Ultraviolet, X-ray, gamma ray, and most infrared light is visible only from orbit. Light-Collecting Area Refracting Telescope The size of a telescope is usually described by the diameter of the primary mirror. The light-collecting area is proportional to the square of the diameter. A 10-m telescope has 100 times the light-collecting power of a 1-m telescope Can detect much fainter objects.

3 The world s largest refracting telescope: Yerkes Observatory, Wisconsin 1 meter diameter Completed 1897 Reflecting Telescope One of the world s largest reflecting telescopes (2x8.4 m): NGC 891 LBT LBT First First Light LightImage 2005 October 12 LBC-B camera NGC 891 LBC Blue Image

4 Hubble Space Telescope (launched 1990) Hubble Telescope Diameter of mirror = 2.4 meters Angular resolution = 0.05 arcseconds Solar Prominence (flare of plasma) Image Resolution Comparison Taking the temperature of stars! Betelgeuse: a reddish star (cooler). Rigel: a bluish stars (hotter). Light: Key Concepts (1) A hot, opaque object produces a continuous spectrum of light. One way to make objects emit light, is to heat them up. (2) Visible light is just one form of electromagnetic radiation. (3) Light can be though of as a wave or as a particle. (4) Light forms a spectrum from short to long wavelengths.

5 Wave Motion Wave Motion Parts Crest Trough Measurements of a wave Wave height the distance between a trough and a crest Wavelength the horizontal distance between successive crests (or troughs) Wave period the time interval for one full wave to pass a fixed position Wave Motion Small wavelength Large frequency Visible light occupies only a tiny sliver of the full spectrum. Large wavelength Small frequency ENERGY As a car or train horn approaches you and then passes by, the pitch of the sound first rises and then falls. This is called the Doppler effect.

6 End of Lecture 4