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Chapter 17: Problem 1

Explain the difference between a star's apparent brightness and its luminosity.

Short Answer

Expert verified
Apparent brightness is how bright the star appears to be from Earth and depends on both its distance and its luminosity. Luminosity, on the other hand, is a measure of the total amount of energy emitted by a star per unit of time and is independent of the star's distance from an observer. Therefore, a star can be very luminous yet appear dim if it is far away, or it can be less luminous but appear very bright if it is closer.

Step by step solution

01

Defining Apparent Brightness

Apparent brightness, also known as apparent magnitude, is a measure of how bright a star appears from Earth. It depends not only on a star's intrinsic brightness but also on its distance from the Earth. The closer a star is to Earth, the brighter it appears.
02

Defining Luminosity

Luminosity of a star is the total amount of energy emitted by it per unit of time. It is also known as the intrinsic brightness of a star. Unlike apparent brightness, luminosity does not depend on the distance of the star from the observer.
03

Explaining the Difference

The main difference between a star's apparent brightness and its luminosity is that while apparent brightness is how bright the star appears to an observer from Earth, luminosity is the actual amount of light the star is giving off. A star can have high luminosity but may appear dim if it is far away, while a less luminous star may appear bright if it is closer to Earth. Thus, the apparent brightness of a star is influenced by both its distance and its luminosity.

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Most popular questions from this chapter

From its orbit around the Earth, the Hipparcos satellite could measure stellar parallax angles with acceptable accuracy only if the angles were larger than about \(0.002\) arcsec. Discuss the advantages or disadvantages of making parallax measurements from a satellite in a large solar orbit, say at the distance of Jupiter from the Sun. If this satellite can also measure parallax angles of \(0.002 \mathrm{arcsec}\), what is the distance of the most remote stars that can be accurately determined? How much bigger a volume of space would be covered compared to the Earth-based observations? How many more stars would you expect to be contained in that volume?

Search the World Wide Web for information about Gaia, a European Space Agency (ESA) spacecraft planned to extend the work carried out by Hipparcos. When is the spacecraft planned to be launched? How will Gaia compare to Hippar\(\cos\) ? For how many more stars will it be able to measure parallaxes? What other types of research will it carry out?

. Sketch the radial velocity curves of a binary consisting of two identical stars moving in circular orbits that are (a) perpendicular to and (b) parallel to our line of sight.

Some giant and supergiant stars are of the same spectral type (G2) as the Sun. What aspects of the spectrum of a G2 star would you concentrate on to determine the star's luminosity class? Explain what you would look for.

Would it be possible for a star to appear bright when viewed through a \(\mathrm{U}\) filter or a \(\mathrm{V}\) filter, but dim when viewed through a B filter? Explain.
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