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Chapter 6: Problem 24

Why are radio telescopes so large? Why does a single radio telescope have poorer angular resolution than a large optical telescope? How can the resolution be improved by making simultaneous observations with several radio telescopes?

Short Answer

Expert verified
Radio telescopes are large to effectively collect and focus long-wavelength radio waves. A single radio telescope has poorer angular resolution than a large optical telescope due to radio waves' longer wavelengths. The resolution can be improved by making simultaneous observations with multiple radio telescopes, a technique known as interferometry.

Step by step solution

01

Understanding the Size of Radio Telescopes

Radio telescopes are large because radio waves have much longer wavelengths than light waves. To collect and focus these long waves effectively to produce a clear image, a larger reflecting area is required. Hence, radio telescopes are usually made larger.
02

Understanding Angular Resolution

Angular resolution is the ability of a telescope to distinguish between two adjacent objects in the sky. Due to the longer wavelengths of radio waves, a single radio telescope has poorer angular resolution than a large optical telescope. In simpler terms, a radio telescope's image is generally more blurred than an image from an optical telescope because it has a bigger 'dot' size on the sky.
03

Improving Resolution Through Simultaneous Observations

The resolution of a radio telescope can be improved by making simultaneous observations with multiple radio telescopes located at different places. This technique is known as interferometry. The data from each telescope are combined to create a 'virtual' telescope that has the same resolution as a single telescope with a diameter equal to the baseline between the individual telescopes. This can give an image quality similar to an optical telescope, effectively improving the 'dot' size or resolution.

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Most popular questions from this chapter

Explain some of the disadvantages of refracting telescopes compared to reflecting telescopes.

Why must astronomers use satellites and Earth-orbiting observatories to study the heavens at X-ray and gamma-ray wavelengths?

The Hobby-Eberly Telescope (HET) at the McDonald Observatory in Texas has a spherical mirror, which is the least expensive shape to grind. Consequently, the telescope has spherical aberration. Explain why this doesn't affect the usefulness of HET for spectroscopy. (The telescope is not used for imaging.)

Compare an optical reflecting telescope and a radio telescope. What do they have in common? How are they different?

Suppose your Newtonian reflector has an objective mirror \(20 \mathrm{~cm}\) ( 8 in.) in diameter with a focal length of \(2 \mathrm{~m}\). What magnification do you get with eyepieces whose focal lengths are (a) \(9 \mathrm{~mm}\), (b) \(20 \mathrm{~mm}\), and (c) \(55 \mathrm{~mm}\) ? (d) What is the telescope's diffraction-limited angular resolution when used with orange light of wavelength \(600 \mathrm{~nm}\) ? (e) Would it be possible to achieve this angular resolution if you took the telescope to the summit of Mauna Kea? Why or why not?
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