Telescopes, Observatories, Data Collection Telescopes 1
Astronomy : observational science only input is the light received different telescopes, different wavelengths of light lab experiments with spectroscopy, properties of matter and radiation space probes to measure conditions in our own solar neighborhood use technology to tweak the models, simulations, graphics Telescopes 2
VISIBLE ASTRONOMY (Optical) visible wavelengths - 4000 A - 7000 A detectable with human eye optics : science of controlling the direction of light Light travels in space in a straight line, a light ray - particles of light (photons) moving in a straight line. Change the direction using lenses, mirrors, prisms. Telescopes 3
Refraction Light crosses one boundary to another, it changes direction - it is bent. The amount that light is bent is dependent on what color it is, i.e., what wavelength. Blue is bent more than red - the shorter the wavelength, the more it is bent. Telescopes 4
Reflection Light bounces off a surface and rebounds at the same angle it had when coming in. Reflection does NOT depend on the wavelength of the light. Science of optics uses refraction and reflection to make images. Telescopes 5
image : gather light rays into the same alignment they had when they left the object visual representation of the object lens : smoothly curved surface, rays are bent, and converge to a point a lens brings light rays to a focus Telescopes 6
extended object : something more than a point source of light a lens brings rays from an extended object to a focus where an image is formed - usually upside-down and smaller focal length : distance from lens to image Telescopes 7
Hubble Space Telescope - Deep Field Telescopes 8
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mirror : f-ratio : a polished surface that reflects light - if flat, image is not distorted; if curved, image is distorted smoothly curved mirror will bring all light to a focus important property that describes a lens or mirror f-ratio = focal length diameter Telescopes 10
Large diameter => small f-ratio => brighter the image telescope : instrument to gather light & allow you to examine an image objective : lens or mirror that brings light to a focus eyepiece : allows you to examine the image Telescopes 11
Refracting Telescope objective is a lens (Galileo s telescope) problem: not all the colors in the light come to focus at the same point - chromatic aberration Telescopes 12
Reflecting Telescope objective is a mirror (Newton s telescope) light does not separate into colors, so no problem with color haloes cheaper to make can be made much larger have to figure out how to look at the image Telescopes 13
Reflecting Telescopes Newtonian - small mirror, tilted at 45 deg. to the path of the light Cassegrain - hole in the objective secondary mirror in the light path fold the path of light cheaper to build Telescopes 14
Functions of a Telescope Gather Light light bucket - collect photons, bring them to focus objects seen in a telescope are brighter than they appear to the naked eye Telescopes 15
LGP (Light Gathering Power) LGP is proportional to (diameter) 2 amount of light depends on the area of the objective a mirror with 2 times the diameter will have times the LGP 4 Telescopes 16
Some Comparisons human eye : diameter = 0.5 cm telescope : diameter = 50 cm How do the LGP s compare? The telescope is 50/.05 = 100 times bigger in diameter. The telescope is (100) 2 (=10,000) times better for gathering light. Telescopes 17
Hale Telescope - 5 m (Mt. Palomar) Mayall Telescope - 4 m (Kitt Peak) How do the LGP s compare? Hale is 5/4 times bigger than the Mayall in diameter. LGP is (1.25) 2 = 1.563 times better in gathering light. Telescopes 18
Resolve fine detail resolution : ability to separate things that appear close together into separate images resolution is measured in angular measure example: 10 cm diameter telescope has a resolution of 1.4 arc sec Telescopes 19
If the separation is more than 1.4 arcsec, you ll see them as separate stars with this telescope. If the separation is less than 1.4 arcsec, you ll see them as a big blob with this telescope. Telescopes 20
Resolution is inversely proportional to diameter Resolution 1 diameter Smaller resolution is better for learning about details. 2 X the diameter means resolution is twice as small (i.e. 2 times better) Telescopes 21
Human eye has a resolution of 1 arcmin. Things that affect resolution : seeing : turbulence in the atmosphere distorts and blurs the image measured in arcsec Solution : put telescopes in space! Resolution would be limited by the optics of the telescope NOT by the Earth s atmosphere. Telescopes 22
Magnify the Image (least important) magnification : apparent increase in an object s size compared to naked eye observation MP = focal length of the objective focal length of the eyepiece Telescopes 23
What s next? very light materials remote observing very large mirrors in segments adaptive optics telescopes in space telescopes on the moon? Telescopes 24
Invisible Astronomy wavelengths not seen by the human eye wavelengths that are generated by very different physical processes allow us to discover astronomical objects we wouldn t ordinarily have seen Telescopes 25
Milky Way in Radio Vesta VLA Arecibo Gamma Ray Moon Telescopes 26
Earth s Atmosphere Radiation that has traveled for billions of years to get here is blocked in the last 100 km of the journey by our atmosphere! IR - blocked by water vapor UV and X-ray blocked by the ionosphere, above 100 km Telescopes 27
ground-based (radio, IR) space-based - rockets, balloons, airplanes, satellites, spacecraft RADIO ASTRONOMY Parabolic dish, focuses the EM rays (in radio wavelengths) to a focal point Telescopes 28
Radio Telescopes detector (receiver) is placed at the focal point, translates the radio signal to a voltage which is then measured and recorded computer then generates a map of these intensities can observe day or night, even on cloudy days for the longer wavelengths Telescopes 29
larger than optical telescopes (100 m!!!) drawback is poor resolution resolution also depends on wavelength being observed long wavelengths, poor resolution SOLUTION : interferometers to create effectively larger diameter telescopes Telescopes 30
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Interferometer Two (or more) telescopes act like parts of one big telescope. Telescopes 33
VLA - Very Large Array, Socorro, NM Telescopes 34
VLBA - Very Long Baseline Array radio dishes from Hawaii to the Virgin Islands resolution of 2 x 10-4 arcsec adding radio telescopes on the moon would give a resolution of 10-6 arcsec Telescopes 35
IR Astronomy some wavelengths from the ground need high, dry climate optics are much the same as for optical astronomy detectors must be different, cooled to 2 K advantages: less hindered by interstellar dust cool objects can be detected things not seen in visible can be detected Telescopes 36
Space-Based IR balloons, satellites IRAS - international collaboration mapped the sky - 200,000 IR sources many related to the process of starbirth UV, X-Ray, Gamma Ray - done from space Telescopes 37
IR Astronomy some wavelengths from the ground need high, dry climate optics are much the same as for optical astronomy detectors must be different, cooled to 2 K advantages: less hindered by interstellar dust cool objects can be detected things not seen in visible can be detected Telescopes 38
Space-Based IR balloons, satellites IRAS - international collaboration mapped the sky - 200,000 IR sources many related to the process of starbirth UV, X-Ray, Gamma Ray - done from space Telescopes 39
Hubble Space Telescope (HST) 2.4 meter mirror goal : faint objects with high resolution, 0.1 arcsec resolution 1200 A to 10,000 A most expensive astronomical project to date Telescopes 40
Hubble Space Telescope Telescopes 41
Image Collection images taken by detectors photographic plates CCD s (charge coupled devices) computer visualizations, false-colors intensity maps Telescopes 42
CCD = Charge Coupled Device Each cell is called a pixel. A pixel captures photons and counts them individually. Telescopes 43