Astronomy, Quiz 1; Chapter 6
The world's largest refracting telescope has a lens of __ meter(s) in diameter
1
Arecibo's angular resolution is about
1 arcminute
Human eye has an angular resolution of ____________; if two dots are separated by less than that, our eyes will not be able to distinguish them individually
1 arcminute
Two most fundamental properties of any telescope:
1) Light collecting area 2) Angular resolution
Images made with invisible light cannot have any natural color because
"Color" is a property only of visible light
Beams of light can interfere with one another because they are waves; this interference limits a telescope's __________
Angular resolution
The smallest angle over which we can tell two dots are distinct
Angular resolution
Long wavelengths of radio signals means that radio telescopes need to be very ______
Big
the fact that lens brings different colors of light into focus at slightly different places
Chromatic aberration
The process of linking two or more individual telescopes to achieve the angular resolution of a much larger telescope
Interferometry
Through _________, radio telescopes can work together to achieve much greater angular resolution
Interferometry
Today, many astronomical images are made from
Invisible light
Radio telescope consisting of 27 smaller dishes, combined area equivalent to 130 meters across or, at times, 40 kilometers
Karl G. Jansky Very Large Array (JVLA)
Picture elements
Pixels
Turbulence tends to limit the angular resolution of ground telescopes to ________________, regardless of their diffraction limit
0.5 arcsecond
The diffraction limit depends on what two criteria:
1) diameter of telescope's primary mirror 2) wavelength of light being observed
Most observations fall into three basic categories:
1) imaging, yields photographs 2) spectroscopy, obtain and study spectra 3) time monitoring, track how an object changes with time
Two reasons that reflector telescopes are mainly used today:
1) light passes through the lens of refracting telescope, so lenses must be made from exceptional material 2) large glass lens are extremely heavy and difficult to stabilize 3) chromatic aberration
Our atmosphere creates 3 other problems that inevitably affect observations:
1) light pollution 2) turbulence in atmosphere 3) fact that most forms of light can't reach Earth's surface
Three types of "cosmic messengers"
1) neutrino, produced by nuclear reactions 2) cosmic rays 3) gravitational waves
Only what kinds of light can be observed from the ground?
1) radio waves 2) visible light 3) the longest wavelengths of UV light 4) small parts of infrared spectrum
Three particularly important telescope sites:
1) summit of Mauna Kea on the Big Island of Hawaii 2) La Palma in Spain's Canary Islands 3) Paranal Observatory site in Chile
Galileo first turned his telescope to the heavens in
1609
A 10-meter telescope has 5 times the diameter of a 2 meter telescope, so its light-collecting area is __ times as great
25, or 5^2
World's largest digital camera
3200 megapixels
Technology that can eliminate turbulence and the blurring associated by making mirrors bounce opposite of blurred stars
Adaptive optics
A point of light in Earth's atmosphere created by a laser
Artificial star
At its most basic, an imaging instrument is simply a
Camera
Offers the best angular resolution of any X-ray telescope yet built; better for making images
Chandra
X ray telescopes
Chandra X-Ray Observatory, NuSTAR mission
Cells within the retina
Cones and rods
Most obvious problems with observing from the ground
Daylight and weather
Technical term for the effects of interference that limit telescope resolution
Diffraction
the angular resolution that a telescope could achieve if it were limited only by the interference of light waves is called its
Diffraction limit
What is one problem of infrared telescopes?
Earth and even the telescope itself emit infrared thermal radiation
Parallel rays of light converge to a point called the
Focus
The place where the image appears in focus is called the
Focus plane
Fermi Space Telescope used to detect what kind of light
Gamma-ray
____________________ observatories use massive detectors to capture photons and determine from whence they came
Gamma-ray
Specially designed mirrors can deflect X rays; X rays merely graze their surface as the rays are directed toward the focal plane
Grazing incidence mirrors
Spectral resolution depends on
How widely the spectrograph spreads out light
Presently, this telescope is the only major space observatory capable of observing ultraviolet observations
Hubble Space Telescope
What is the most famous observatory in space
Hubble Space Telescope
NASA's SOFIA carries a 2.5 meter _____ telescope that looks out through a large hole cut in the body of a 747
Infrared
The atmosphere glows at many ____________ wavelengths
Infrared
How much total light a telescope can collect at a time
Light collecting area
We characterize a telescope's size by the diameter of its
Light collecting area
The results of time monitoring are often shown as __________________: graphs that show how an object's intensity varies with time
Light curves
Our atmosphere scatters bright lights of cities at night, creating ________________
Light pollution
Basic components of the human eye
Pupil, lens, retina
The Arecibo telescope stretches 305 meters (1000 ft) across a natural valley in Puerto Rico and is the world's largest single telescope; it is what kind of telescope?
Radio
The atmosphere does not scatter most __________________, so these telescopes can operate day and night and under cloudy skies
Radio
To which kind of telescope would the Moon be useful (acts as a shield to block out Earth's interference)
Radio
A ______________ telescope uses a curved primary mirror to gather light; this mirror reflects light to a secondary mirror that reflects light to a focus point where eyes and instruments can observe it
Reflecting
Nearly all telescopes used in research today are ________________
Reflectors
A ___________ telescope operates much like an eye, using glass lenses
Refracting telescope
Kind of telescope that Galileo used
Refracting telescopes
A change in direction in which light is travelling
Refraction
The most common kind of telescope in the world
Satellite dish
The information we can glean from a spectrum depends on the
Spectral resolution
Instruments called ________________ use diffraction gratings to separate the various colors of light into spectra, which are then recorded with a detector
Spectrographs
The ever changing motion in the atmosphere, or _____________ bends light in constantly shifting patterns
Turbulence
What causes the twinkling of stars?
Turbulence
Image formed by a lens is
Upside down
What kind of light rays have sufficient energy to penetrate many materials, including ordinary mirrors
X rays
Has largest collecting area of any other X-ray telescope; better for making spectra
XMM-Newton
The ultimate limit of a telescope's resolving power comes from
the properties of light