Chapter 6 Flashcards
We collect and measure what from astronomical sources
through the use of a what?
electromagnetic radiation, telescopes
a telescope is a what collecting what of light as they what?
light bucket, photons, rain down
The most important functions of a
telescope are (1) to collect the what from an astronomical source and (2) to focus all the light into a what or an what?
faint light, point, image
Telescopes that collect visible radiation use a what or what to gather the light.
lens, mirror
We can compare their light-gathering power by comparing the what, or what, of the opening through which light travels or reflects.
apertures (diameters)
The light gathering power of a telescope is proportional to its what squared.
diameter
optical telescopes-those designed to collect what.
visible light
Telescopes can form images in one of two ways: using lenses
(what) or mirrors (what).
refracting, reflecting
When light passes through a lens, the light beam bends (or what)
and gets focused at a point.
refracts
A telescope that uses lenses to focus an image is called a what
telescope.
refracting
when light passes through a lens, the different wavelengths
of light bend by different amounts, causing the image to be
blurred. This is known as what?
chromatic aberration
which telescope is used more?
reflecting telescopes
about how large can a reflecting telescope be built?
40 m in diameter
The best observatory sites are on what, far from the what and
what of cities?
mountains, lights, pollution
what poses a challenge for clear viewing of a telescope?
earths atmosphere
Even on a clear night, the atmosphere filters out a certain amount of starlight, especially in the what, where the absorption is due primarily to what. Astronomers therefore prefer what, generally found at what altitudes?
infrared, water vapor, dry sites, high
Observatories are best located at least how many miles from the nearest large city.
100 miles
what refers to the precision of detail present in an image: that is, the smallest features that can
be distinguished.
resolution
One factor that determines how good the resolution will be is the what of the telescope.
size
The resolution of an image is measured in units of what on the sky, typically in units of what.
angle, arc seconds
One arc second is what degree, and there are 360 degrees in a full circle
1/3600 degree
Many astronomical objects emit what
radio waves
the quality of resolution depends upon the what of the what that the telescope is gathering.
wavelength, radiation
the what the wave is, the harder it is to obtain fine detail
longer
To overcome this difficulty, radio astronomers have learned to sharpen their images by linking two or more radio telescopes together electronically. Two or more telescopes linked together in this way are called an
what
interferometer
what is a technical term for the way that multiple waves interact with each other when they arrive
in our instruments, and this interaction allows us to coax more detail out of our observations.
interference
Astronomers can link several telescopes together into an what.
interferometer array
Radio telescopes can also perform what
radar imaging
With infrared observations, astronomers can detect what parts of cosmic objects, such as the dust
clouds around star nurseries and the remnants of dying stars, that visible-light images don’t reveal.
cooler
the what was the most successful space telescope
the Hubble telescope (2.4 m)
when was the Hubble space telescope launched
1990
what telescope is next to the Hubble in success?
James webb telescope (6 m)
