Why look at different frequencies of light? Cooler objects are only visible at long wavelengths:...
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Transcript of Why look at different frequencies of light? Cooler objects are only visible at long wavelengths:...
Why look at differentfrequencies 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
GreenBankTelescope
Green Bank,W.Va.
The dishwould holdFulton 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 thesetelescopes 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 invisible wavelengths !!
ISO – theInfraredSpaceObservatory
EuropeanSpaceAgency (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 Telescopeor 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 holeat 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