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Chapter 17: Problem 6

Briefly describe how you would determine the luminosity of a nearby star. Of what value is knowing the luminosity of various stars?

Short Answer

Expert verified
The luminosity of a star can be determined by measuring the star's apparent brightness and its distance from Earth, then applying the inverse square law of light. Knowledge of a star's luminosity is valuable as it allows us to decode other properties of the star, such as size, surface temperature, its stage in the stellar life cycle, age, and the chemical elements within it.

Step by step solution

01

Understand the Concept of Luminosity

Luminosity refers to the total amount of energy emitted by a star per unit of time. It's a measure of the star's power output.
02

Determine Apparent Brightness

Apparent brightness is the measure of the star's brightness as seen from Earth. It can be measured using a photometer or other light-measuring instruments.
03

Measure the star's distance from Earth

The distance of stars can be measured using various methods such as parallax method, cosmic distance ladder, among others.
04

Apply the Inverse Square Law

The inverse square law of light can be used to calculate a star's luminosity. The law states that the intensity of light is inversely proportional to the square of the distance. That means, if the distance doubles, the brightness decreases by a factor of four. So, if we have the value of apparent brightness and the distance, we can calculate the luminosity by using this formula: Luminosity = Apparent Brightness x 4π x (Distance)^2.
05

Understand the Importance of Star Luminosity

Knowledge about the luminosity of various stars is valuable as it helps us deduce other properties of stars, such as their size, surface temperature, and stage in the stellar life cycle. Luminosity can also permit deductions about a star's age and the chemical elements present in it.

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Most popular questions from this chapter

Sketch a Hertzsprung-Russell diagram. Indicate the regions on your diagram occupied by (a) main-sequence stars, (b) red giants, (c) supergiants, (d) white dwarfs, and (e) the Sun.

What is the inverse-square law? Use it to explain why an ordinary lightbulb can appear brighter than a star, even though the lightbulb emits far less light energy per second.

The star HIP 72509 has an apparent magnitude of \(+12.1\) and a parallax angle of \(0.222\) arcsecond. (a) Determine its absolute magnitude. (b) Find the approximate ratio of the luminosity of HIP 72509 to the Sun's luminosity.

The star Zubenelgenubi (from the Arabic for "scorpion's southern claw") has apparent magnitude \(+2.75\), while the star Sulafat (Arabic for "tortoise") has apparent magnitude \(+3.25\). Which star appears brighter? From this information alone, what can you conclude about the luminosities of these stars? Explain.

A fellow student expresses the opinion that since the Sun's spectrum has only weak absorption lines of hydrogen, this element cannot be a major constituent of the Sun. How would you enlighten this person?
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