Astronomy 1010 Planetary Astronomy Fall_2015 Day-23

Course Announcements SW-chapter 6 posted: due Fri. Oct. 23 Exam-2 will be returned on Friday 1 st Quarter Observing night: Tuesday, Oct. 20; 7:30pm

Useful Information for Next Lab Lenses & Telescopes In Class. Equipment required. Print the instructions BEFORE you come to class!

Lab This Week Lenses and Telescopes

 Electronic detectors record photons on pixels.  Photons create a signal in the array.  CCDs = charge-coupled devices (such as digital cameras).

 The electronically recorded images can greatly exceed photographs in quality.  CCD = astronomer’s detector of choice.

Red Green Blue

Red Green Blue

Color separation is useful in a prism so that we can obtain a spectrum of light Since it is meant to be separated we don’t call it an aberration. Instead, it is called dispersion

 Spectrographs disperse the incoming light into its component wavelengths.  Lets astronomers study the spectrum of an object’s light.

A diffraction grating works on interference of light waves Diffraction is much more efficient at separating light into its colors than dispersion

Unfortunately, diffraction also leads to problems Look closely enough at stars and they aren’t just points of light but rings, too

The best spectrographs use diffraction gratings

The spectrograph/CCD produces a black & white spectrum

Multitasking Saves Time

Spectrum But visible light is only one type of electromagnetic radiation (light) emitted by stars Astronomers are truly interested in the entire spectrum of Light!

 The atmosphere does not transmit all light.  Nearly all X-ray, ultraviolet, and infrared wavelengths are blocked.  Satellites are needed for these wavelengths.

Consider This Class as Seen in Different Wavelengths of Light!

Orion in Infrared!

HST Views of Orion Nebula showing stars hidden in clouds

Observations at other wavelengths are revealing previously invisible sights UV Ordinary visible Infrared Map of Orion region

 Radio telescopes are large, steerable parabolic dishes with antennas.  Allow astronomers to study radio waves.  Wavelengths of a centimeter to about 10 meters.  Radio waves can pass through gas and dust.

Radio wavelength observations are possible from Earth’s surface

Observing with Radio Waves Long Wavelength…poor resolution

Under the dish at Arecibo

The Very Large Array (VLA)

 Single radio telescopes have poor resolution due to the long wavelengths.  Interferometric arrays combine the signals from many telescopes, increasing resolution.

 Two electromagnetic waves in the same location will produce interference.  The waves will either enhance or detract from each other, resulting in constructive or destructive interference.  This can result in spectral dispersion. CONNECTIONS 6.2

 Airborne observatories: raise the telescope above clouds and water vapor (infrared astronomy).  Satellites in orbit: detect wavelengths that the atmosphere blocks (ultraviolet and X-rays).  Can produce very sharp images (e.g., the Hubble Space Telescope).

Astronomers use different instruments to look at light of different wavelengths - sometimes, we even have to go above Earth’s atmosphere. That Darned Atmosphere