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Transcript
Why look at different frequencies of light? • Cooler objects are only visible at long wavelengths: radio, microwaves, IR. • Hotter objects are only visible at short wavelengths: UV, X-rays, -rays. Radio Telescopes • Detects cool gases: H+ H H2 • Can detect molecules out in space: • • • • • oxygen O2 carbon dioxide CO2 hydrogen cyanide HCN formaldehyde H2CO Ethanol CH3COOH Advantages / Problems • Operates night or day • Atmosphere doesn’t absorb radio waves • Poorest resolution of any type of light (doesn’t see details well) • Solution is to make antennas (dishes) VERY large Arecibo Radio Telescope, Arecibo, Puerto Rico Puerto Rico Green Bank Telescope Green Bank, W.Va. The dish would hold Fulton Field Radio Interferometry – a Recipe • Take 2 (or more) widely separated radio telescopes… • Electronically blend their signals… • Result is as if you had a telescope with a diameter equal to the distance between the two separate telescopes. • VASTLY improves resolution! Very Large Baseline Array sites across the US. Together these telescopes form a huge interferometer. Infrared (IR) Telescopes • Very similar to visible wavelength telescopes, except for the detector, called a bolometer. • IR scopes detect heat from warm gas or warm objects. “Warm” means not hot enough to glow in visible light. • These scopes must be kept very cold or the heat the scope itself radiates swamps out what they’re looking for. What kinds of objects? • IR telescopes “see” warm gas, molecules & dust. In some cases, they can look through cooler dust to see what’s inside the dust clouds! • Since stars form where there’s lots of dust, these scopes are great for looking inside dusty nebulas where new stars form. We can’t see everything just in visible wavelengths !! ISO – the Infrared Space Observatory European Space Agency (ESA) Orbital Telescopes • Why put a telescope in orbit? • Gets it above the atmosphere with all its dust, ozone, water vapor, and CO2 that absorb so much of what we want to see. • What’s the most famous orbiting telescope? If you said the Hubble Space Telescope or HST, you’re right! HST does detect visible light • It also detects ultraviolet light. • 2.4 meter mirror = 230,400 eyes! • Resolution is 0.0126 arcsecond or 1 / 3,500,000th of a circle. • We’re used to seeing photos like these! X-ray & Gamma Telescopes • “Sees” very hot objects: • Black Holes • Pulsars & Neutron Stars • Supernovas • VERY good resolution – sees fine details NGC 4261 – a huge black hole at the center of a distant galaxy A supernova – an exploding star What’s left after the explosion – a supernova remnant. This one’s called Cassiopeia A. The Crab Nebula in visible light (left) & X-rays (right). At the center of the Crab Nebula – a PULSAR