Astronomy 1020-H Stellar Astronomy Spring_2015 Day-21

Blizzard of 2015 – Part - 4

Course Announcements Exam-2: Fri. 3/20 Chapters 5 & 6  I will collect the L-T books at this time. Drop “Proper Motion of a Star” lab Smartworks Chapters 6: Due Mon. 3/23 Apr. 2 – Last day to drop a class. Midterm grades are delayed until Thursday  Based on Exam-1 and labs TONIGHT: Dark Sky Observing Session: 8:30pm at the Observatory. Map is on apsu.edu/astronomy

 Resolution = smallest details that can be separated.  The longer the focal length, the better the separation of two objects or features.  Diffraction, or blurring of an image, sets the best possible resolution.  The diffraction limit depends on the ratio of wavelength-to-telescope aperture.

 The ultimate resolution of a telescope is set by the diffraction limit.  The angle subtended by the smallest resolution, θ, is determined by the ratio of the wavelength of light being studied to the aperture diameter.  1 arcsecond = 1/3,600 of a degree.  Human eye: MATH TOOLS 6.2

Concept Quiz—Bigger Telescopes Why do astronomers want to build bigger telescopes? A.to eliminate the effects of astronomical seeing B.to search for life on Mars C.to observe fainter or more distant objects

 Earth’s atmosphere degrades images.  Astronomical seeing = limit on resolution due to the atmosphere.  Space-based telescopes do not have this problem.

 Adaptive optics can help correct for this atmospheric distortion.  Earth-based image quality can compete with the Hubble Space Telescope in the visible.

 The eye is a refracting telescope.  It collects light and focuses an image.  The faintest we can see is limited by: Integration time: the time over which the eye can add up photons. Quantum efficiency: the likelihood that a photon falling on the retina will produce a response.

 Photography opened the door to modern astronomy.  Captured images on photographic plates.  Increased integration time comes with longer exposures.  Expensive, slow, and messy.

 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.

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