Astronomy 1020-H Stellar Astronomy Spring_2016 Day-18

Course Announcements Dark Night Observing: Tonight 2/29 & Wed. 3/2 – 7:30pm at the APSU Observatory – Wx Dependent Exam-2 – Fri. 3/4 Chapters 5 & 6 I will collect the L-T books on Fri. Mar. 4 Smartworks Chapters 5 & 6: Due Fri. 3/4 Spring Break Mar (Sat.-Sun.) APSU Research and Creativity Forum April 15, 2016 Abstracts are due: 4:00pm Fri., March 18 Feb. 29 – Last day to drop with an automatic “W” Apr. 1 – Last day to drop a class with W, F, FA March 7 and 8 – Active Shooter Exercise in SSB

 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.

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

 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.

 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).

Concept Quiz—Mountain Telescopes Why do astronomers build telescopes on mountains? A.to be closer to the objects they are observing B.to minimize the effects of the atmosphere C.to observe wavelengths such as X-rays or ultraviolet light

 Spacecraft have visited or flown by all the classical planets.  Flybys and orbiters observe from afar.  Landers, rovers, and atmospheric probes are more direct, and some can return samples.

 Particle colliders probe physics of protons, neutrons, neutrinos, and atomic nuclei.  Can help astronomers understand the early universe and structure formation.

 In a few cases, astronomers capture things other than light: Neutrinos—light subatomic particles that are extremely difficult to detect. Gravitational waves—distortions in spacetime predicted by relativity.

Concept Quiz—Telescopes Pick the incorrect answer: Why build telescopes on the ground when we can launch them into space? A.Ground-based telescopes are useful for studying visible and infrared light. B.Ground-based telescopes get much higher resolution. C.They are far cheaper to build and fix than space-based telescopes.

 Computers are essential for astronomy.  Help in data analysis.  Simulations and models help to investigate complex situations.

 A microwave telescope provided more evidence for the Big Bang, revealing the presence of the cosmic microwave background radiation (CMB).

 Technology and science are symbiotic.  New technological advances lead to new methods of scientific observation and experimentation.  New scientific discoveries spur improvements in instrumentation. PROCESS OF SCIENCE