Chapter 6 Mastering Astronomy

Which technology can allow a single ground-based telescope to achieve images as sharp as those from the Hubble Space Telescope?

adaptive optics

To achieve the same angular resolution as a visible-light telescope, a radio telescope would need to be

in space

The twinkling of stars is caused by

motion of air in our atmosphere

How does your eye focus light? How is a glass lens similar? What do we mean by focal plane of a lens?

By bending light to a focus point on the retina; by bending parallel rays of light to a focus point of the lens; focal plane is where the image appears in focus.

How does a camera record light? How are images affected by exposure time? What are pixels?

Camera has a small opening for light to enter, like the pupil of the eye, lens bends the light, bringing it to a focus on a detector that makes a permanent record of the image. Longer exposure= more detail. Pixels- electronic chips that are physically divided into grids of picture elements, used in modern detectors.

I have a reflecting telescope in which the secondary mirror is bigger than the primary mirror.

False

I wanted to see faint details in the Andromeda Galaxy, so I photographed it with a very short exposure time.

False

Thanks to adaptive optics, telescopes on the ground can now make ultraviolet images of the cosmos.

False

What do we mean when we speak of images made from invisible light, such as x ray or infared images? What do the colors in these images mean?

Images made with invisible light cannot have any natural color because color is a property only of visible light. We can use color-coding to interpret them. Sometimes color can respond to different energy levels or according to light intensity or to physical properties of objects in the images.

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

Imaging: yields photographs of astronomical objects. Spectroscopy: astronomers obtain and study spectra. Time monitoring: tracks how a distant object's brightness changes with time.

What is interferometry can how can it improve astronomical observations?

Interferometry: linking of two or more individual telescopes to achieve angular resolution of a much larger telescope; works by taking advantage of wave-like properties of light that cause interference.

What are the 2 key properties of a telescope, and why is each important?

Light-collecting area: determines how much light it gathers. angular resolution: determines how much detail we can see in its images.

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

Only radio waves, visible light, the very longest wavelengths of ultraviolet light, and small parts of the infared spectrum can be observed from the ground. Space telescopes are important because they allow us to observe the rest of the electromagnetic spectrum.

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

Radio telescope: angular resolution important bc they aren't used to make images of the satelites in space

How do reflecting telescopes differ from refracting telescopes? Which type is more commonly used by professional astronomers, and why?

Refracting telescope: operates like an eye, using transparent glass lenses to collect and focus light. Reflecting telescope: uses a precisely curved primary mirror to gather light. Reflecting telescopes are more commonly used because only the reflecting surface of a mirror must be precisely shaped, quality of the underlying glass is not a factor, and since mirror is located at the bottom its weight isn't a problem.

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

Scattering of human-made light, blurring of images by atmospheric motion, and the fact that most forms of light cannot reach the ground at all. Adaptive optics help eliminate blurring.

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

Spectral resolution is the amount of detail we can see. The higher the spectral resolution, the more detail. BUT, b/c the spectral resolution depends on how widely the spectrograph spreads out the light, if the light is spread out more, you need more total light in order for it to be recorded successfully. So making a spectrum of an object requires a longer exposure time than making an image, and higher resolution spectra require longer exposures than low-resolution spectra.

If you lived on the moon, you'd never see stars sparkle.

True

True or false: The image was blurry because the detector was not placed at the focal plane.

True

Interferometry uses two or more telescopes to achieve

angular resolution equivalent to a larger telescope

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

diffraction limit: the angular resolution that a telescope could achieve if it were limited only by the interference of light. Larger telescope= smaller diffraction limit. Diffraction limit is larger for light with longer wave length.

How much greater is the light-collecting area of a 6-meter telescope than that of a 3-meter telescope?

four times

Where should you put a telescope designed for ultraviolet observations?

in Earth orbit

What does it mean if you see the color red in an X-ray image from the Chandra X-ray observatory?

it depends: the colors are chosen arbitrarily to represent something about the X rays recorded by the telescope.

The Hubble Space Telescope obtains higher-resolution images than ground-based telescopes because...

it is larger