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Chapter 14: Problem 42

Suppose you wanted to search for trans-Neptunian objects. Why might it be advantageous to do your observations at infrared rather than visible wavelengths? (Hint: At visible wavelengths, the light we see from planets is reflected sunlight. At what wavelengths would you expect distant planets to emit their own light most strongly? Use Wien's law to calculate the wavelength range best suited for your search.) Could such observations be done at an observatory on the Earth's surface? Explain.

Short Answer

Expert verified
Observations of trans-Neptunian objects can be more efficient at infrared wavelengths. This is because these objects emit their own light most strongly within the infrared spectrum, as calculated using Wien's law. However, such observations might be challenging to perform from Earth's surface due to atmospheric interference with infrared light.

Step by step solution

01

Understanding the Difference between Visible Light and Infrared

Visible light and infrared have different properties. Visible light is what the human eye can see, while infrared is beyond our visualization but can be detected by certain equipment. Often, distant celestial bodies don't emit light in the visible spectrum, but in the infrared which makes infrared ideally suited to study them.
02

Applying Wien's Law

Wien's law, which states that the peak wavelength of light emitted by an object (λ_max) is inversely proportional to its absolute temperature (T), can be used to calculate the inclination towards infrared wavelengths. The equation for Wien's law is \(λ_max = \frac{b}{T}\), where \(b\) is Wien's constant (\(2.9*10^{-3} m*K\)). Given that the temperature of outer planets like Neptune is approximately 50 K, the peak wavelength these planets emit their light at would be \(λ_max = \frac{b}{T} = \frac{2.9*10^{-3} m*K}{50 K} = 58 * 10^{-6} m\), which is within the infrared spectrum.
03

Practicality of Performing Observations from Earth

As advantageous as it might be to observe in infrared, it is not always feasible from Earth's surface due to atmospheric interference. Earth's atmosphere absorbs much of the infrared light, making ground-based observations challenging. Thus, such observations are generally conducted from space, or from high altitude locations on Earth where atmospheric interference is less.

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Most popular questions from this chapter

If you have access to a large telescope, make arrangements to view Neptune. Like Uranus, Neptune is best seen at or near opposition and can most easily be found using a star chart. Can you see a disk? What is its color?

Briefly describe the evidence supporting the idea that Triton was captured by Neptune.

How do the orientations of Uranus's and Neptune's magnetic axes differ from those of other planets?

The brightness of sunlight is inversely proportional to the square of the distance from the Sun. For example, at a distance of \(4 \mathrm{AU}\) from the Sun, sunlight is only \((1 / 4)^{2}=1 / 16=\) \(0.0625\) as bright as at \(1 \mathrm{AU}\). Compared with the brightness of sunlight on the Earth, what is its brightness (a) on Pluto at perihelion (29.649 AU from the Sun) and (b) on Pluto at aphelion (49.425 AU from the Sun)? (c) How much brighter is it on Pluto at perihelion compared with aphelion? (Even this brightness is quite low. Noon on Pluto is about as dim as it is on the Earth a half hour after sunset on a moonless night.)

In 2006 the International Astronomical Union changed Pluto's designation from planet to dwarf planet. One criterion that Pluto failed to meet was that a planet must have "cleared the neighborhood" around its orbit. In what sense has Pluto not done so? In what sense have the eight planets (Mercury through Uranus) cleared their neighborhoods? Do you agree with this criterion?
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