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Chapter 32: Problem 8

When the Moon passes in front of a star, the starlight intensity fluctuates before going to zero instead of dropping abruptly. Explain.

Short Answer

Expert verified
The gradual drop in star brightness when the Moon passes in front of it is due to two phenomena: light diffraction, which allows light to bend around the Moon, and Earth’s atmospheric interference, causing multiple refractions and redistributions of the starlight.

Step by step solution

01

Understand Light Diffraction

Physics teaches that light tends to bend around objects placed in its path, and this phenomenon is known as diffraction. When the moon is transitioning in front of a star, it doesn't block the starlight immediately and completely. Some starlight will diffract around the Moon and this is why there is observable fluctuation in the intensity of the starlight before it goes to zero.
02

Understand Earth’s Atmosphere Influence

The Earth's atmosphere acts as a dense medium compared to the vacuum of space. When starlight passes through the Earth's atmosphere, it refracts numerous times due to the variance in air density with altitude. This scattering of light will also cause fluctuations in the intensity of the starlight before the Moon completely blocks it out.
03

Combine the Concepts

The combination of the diffraction of light around the Moon and the refraction of light through the Earth's atmosphere explains the phenomenon observed. It's a complex interplay of these circumstances that results in the observed fluctuation of starlight intensity as the Moon passes in front of a star. Hence, instead of a sudden drop to zero, the intensity diminishes gradually.

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Most popular questions from this chapter

Green light at \(520 \mathrm{nm}\) is diffracted by a grating with 3000 lines/cm. Through what angle is the light diffracted in (a) first and (b) fifth order?

The primary maxima in multiple-slit interference are in the same angular positions as those in double-slit interference. Why, then, do diffraction gratings have thousands of slits instead of just two?

X-ray diffraction in potassium chloride (KCl) results in a first order maximum when 97 -pm-wavelength \(\mathrm{X}\) rays graze the crystal plane at \(8.5^{\circ} .\) Find the spacing between crystal planes.

A double-slit system is used to measure the wavelength of light. The system has slit spacing \(d=15 \mu \mathrm{m}\) and slit-to-screen distance \(L=2.2 \mathrm{m} .\) If the \(m=1\) maximum in the interference pattern occurs \(7.1 \mathrm{cm}\) from screen center, what's the wavelength?

Suppose one of the 10 -m-diameter Keck Telescopes in Hawaii is trained on San Francisco, \(3400 \mathrm{km}\) away. Assuming \(550-\mathrm{nm}\) light, and ignoring atmospheric distortion, would it be possible to read (a) newspaper headlines or (b) a billboard sign at this distance? (c) Repeat for the case of the Keck optical interferometer, formed from the two 10 -m Keck Telescopes and several smaller ones, with a 50 -m effective aperture.
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