Astronomy Chapter 6 Review

what are the three basic categories of astronomical observation, and how is each conducted?

Imaging which yields photographs or images of astronomical objects. Spectroscopy, in which astronomers obtain and study spectras. and Time Monitoring which tracks how an object changes with time.

two key properties of a telescope and why is it important?

A telescopes light-collecting area tells us how much total light it can collect at one time. for example a "10-meter telescope" has a light collecting area that is 10 meters in diameter. Angular resolution is the smallest angle over which we can tell that two dots- or two stars- are distinct. this allows us to detect starts that we might not be able to find without a telescope.

what is interferometry and how can it improve astronomical observation?

Interferometry is the linking of two or more telescopes together to achieve the angular resolution of a much larger telescope. it works by taking advantage of the wavelike properties of light that cause interference. The procedure relies on precisely timing when radio waves reach each dish and using computers to analyse the resulting interference patterns. they can get a higher angular resolution with a smaller overall diameter than one telescope with a very large diameter.

List three ways in which Earth's atmosphere can hinder astronomical observations. What problem can adaptive optics help with?

Light Pollution is from the city lights at night and hinders the astronomers view of the night sky. Twinkling and Atmospheric Turbulence is what we call it when the air currents are continually moving and mixing around constantly changing the atmosphere's light-bending properties. Lastly, there is the fact that most forms of light cannot even penetrate our atmosphere at all and therefore never make it to ground. Adaptive Optics eliminates much of the blurring and allow telescopes to achieve angular resolution close to their diffraction limit.

what is the Diffraction limit, and how does it depend on a telescope's size and the wavelength of light being observed?

The angular resolution that a telescope could achieve if it were limited only by the interference of light waves is called its diffraction limit. for any particular wavelength of light a larger telescope has a smaller diffraction limit, meaning it can achieve a better (smaller) angular resolution.

How does your eye focus light? What do we mean by the focal plane of a lense?

The pupil controls how much light enters your eye; it dilates in low light and constricts in bright lights. a focal plane is the place where the image appears in focus. with perfect vision the focal place is right on the retina.

how do reflecting telescopes differ from refracting telescopes? which type is more commonly used by professional astronomers and why?

a refracting telescope operates much like an eye, using a transparent glass lense to collect and focus light. A reflecting telescope uses a precise curved primary mirror to gather light. then reflects to a secondary mirror which reflects it to where the eye piece can observe it. astronomers use the reflecting mirror. firstly because light passes through the lense of a refracting telescope, lenses have to be made of a precise high-quality glass where in reflecting telescopes only the reflecting surface has to be precise. secondly, glass lenses are heavy and pose a problem of morphing over time of being help up by only their edges. where as a mirror is placed at the bottom and does not pose a weight threat.

what do we mean when we talk about images made from invisible light, such as x-ray or infrared images? what do the colors in these images mean?

invisible light is light that the human eye cannot see but can be captured by specialized detectors. images made with invisible light cannot have any natural color, because "color" is a property only in visible light. however, we can use color coding to show the different intensities of the light or to show physical properties of the objects in the image.

describe how deeply each portion of the electromagnetic spectrum penetrates Earth's atmosphere. Based on your answer, why are space telescopes so important to our understand of the universe?

only radio waves, visible light, and small parts of the infrared spectrum can be observed from the ground. Therefore the most important reason for putting telescopes into space is to allow up to observe the rest of the electromagnetic spectrum.

what do we mean by spectral resolution? Why is it higher spectral resolution more difficult to achieve?

spectral resolution goes hand in hand with how much detail we can see. the higher the spectral resolution the more detail we can see. higher spectral resolution comes with a price, it depends on how widely the spectrograph spreads out this light that it collects. better detail requires a longer exposure time.

how do telescopes for invisible wavelengths differ from those for visible light? answer for each major wavelength band and give examples of important observatories in those bands.

telescopes for invisible wavelengths require variations on the basic design used for visible-light telescopes. Radio Telescopes do not need angular resolution to decode the waves themselves. all radio waves can be observed from the ground and do not need to be put in space. the largest Radio Telescope is the Arecibo dish in Puerto Rico. Infrared Telescope observes the infrared wavelengths which are close enough to the visible light spectrum to behave quite similarly. the largest one today is NASA's Spitzer Space Telescope that is now up in space to avoid Earths heat rays. Ultraviolet Telescope is similar to both Infrared and visible wavelengths to behave similarly. however the atmosphere absorbs most of the ultraviolet light so they have to be deployed into space. One major Ultraviolet Telescope is the Galaxy Evolution Explorer. x-Ray Telescopes are very difficult for astronomers to use because they tend to penetrate most materials including mirrors. Therefore they have to take different approaches to obtain the information. one major telescope is NASA's Chandra X-Ray Observatory. Gamma-Ray Telescopes are ever more challenging that X-Ray Telescopes they penetrate most materials. They need massive detectors to capture gamma ray photons. one telescope is the Fermi Gamma-Ray Observatory.

how does a camera record light? how are images affected by exposure time? what are pixels?

the light comes through a small opening at the front and then the lense bends the light bringing it to a focus on a detector thats makes a permanent record of the image. exposure is controlled by the shitter of a camera. light reaches the detector only when the shutter is open. Modern detectors that use electronic chips that are physically divided into grids or picture elements, or pixels for short.