Lecture 6 Flashcards
Imaging
Taking pictures of astronomical objects (Eg. Planets, stars, galaxies)
Spectroscopy
Breaking light into spectra, i.e. analyzing characteristic electromagnetic emission or absorption features of astronomical objects
Timing
Measuring how light output varies with time ( or more generally, how emission of electromagnetic radiation varies with time)
Imaging
Astronomical detectors usually record only one color of light at a time
Several images must be combined to make full color pictures
Can record forms of light our eyes can’t see
Spectroscopy
A spectrograph separates the different wavelengths of light before they hit the detector
Graphing relative brightness of light at each wavelength shows the details in a spectrum
Timing
A light curve represents a series of brightness measurements made over a period of time
What are the most important properties of a telescope?
Collecting area determines how much light a telescope can gather
Angular resolution is the minimum angular separation a telescope can distinguish
What are the 2 basic designs of telescopes
Refracting telescopes focus light with lenses
Reflecting telescopes focus light with mirrors
The vast majority of professional telescopes are reflectors
What do astronomers do with telescopes
Imaging, Spectroscopy and Timing
how does Earths Atmosphere affect ground based observations
The best ground bases sites for astronomical observing are
Calm
High
Dark
Dry
Light Pollution
Scattering of human made light in the atmosphere is a growing problem for astronomy
Where are the best observing sites
Atop remote mountains in hot, dry climate
Transmission in Atmosphere
Only radio and visible light pass easily through Earths atmosphere
We need telescopes in space to observe other forms
How can we observe invisible light?
A standard satellite dish is essentially a telescope for observing radio waves
Radio telescopes
A radio telescope is like a giant mirror that reflects radio waves to a focus
The Arecibo radio telescope had a diameter of about 300 meters
Infared and Ultraviolet Telescopes
Infared and Ultraviolet light telescopes operate like visible light telescopes but need to be above atmosphere to see all wavelengths
X ray telescopes
X ray telescopes also need to be above the atmosphere
Focusing of X rays requires special mirrors
Mirrors are arranged to focus x ray photons through gazing bounces off the dish
Gamma - Ray Telescopes
Gamma Ray telescopes also need to be in space
Focusing Gamma rays is extremely difficult, and high energy gamma rays are also rare
How can we observe invisible light?
Telescopes for invisible light are usually modified versions of reflecting telescopes
Many of the telescopes used for observing invisible light are in space
What kind of waves can be observed with ground based telescopes
Visible light and Radio waves
