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Pathways to Astronomy

Stephen E. Schneider

Chapter 54

Light and Distance - all with Video Answers

Educators

Chapter Questions

02:24

Problem 1

The faintest visible stars deliver only about $10^{-14}$ watts to your eye. A typical visible-wavelength photon has an energy of about $3 \times 10^{-19}$ joules. How many photons per second are you seeing?

Khoobchandra Agrawal
Khoobchandra Agrawal
Numerade Educator
01:43

Problem 2

In the text we estimated the distance to Alpha Centauri by assuming that it has the same luminosity as the Sun. Use the measured brightness $\left(3 \times 10^{-8} \text {watts } / \mathrm{m}^{2}\right)$ and its distance (4.4 ly) to calculate Alpha Centauri's actual luminosity, How many times bigger than the Sun's luminosity is this?

Himanshu Garg
Himanshu Garg
Numerade Educator
07:59

Problem 3

Suppose star A is 36 times brighter than star $\mathrm{B}$, but we have reason to believe that they have the same luminosity.
a. Which is more distant?
b. How many times more distant is it than the other star?

Daniel Azubuike
Daniel Azubuike
Numerade Educator
04:09

Problem 4

Star $C$ and star $D$ are at the same distance from us, but star D is 10,000 times more luminous than star $C .$ How do their brightness levels compare?

Ren Jie Tuieng
Ren Jie Tuieng
Numerade Educator
04:09

Problem 5

How do the magnitudes of stars $C$ and $D$ in problem 4 compare?

Ren Jie Tuieng
Ren Jie Tuieng
Numerade Educator
01:23

Problem 6

The star Deneb has an apparent magnitude of 1.25 and an absolute magnitude of $-8.5 .$ What two statements can you make about it, based on this data?

Malisa Brill
Malisa Brill
Numerade Educator
00:52

Problem 7

Star A has a magnitude of 3.5. Star B has a magnitude of
$-1.5 .$ Which star is brightest, and by what brightness ratio?

Julie Silva
Julie Silva
Numerade Educator
00:29

Problem 8

If you observed the Sun from Antares, what apparent magnitude would it have?

Mitchel Vereen
Mitchel Vereen
Numerade Educator
01:24

Problem 9

Proxima Centauri is approximately the same distance from Earth (slightly less than 4.3 ly) as Alpha Centauri A, but it has an apparent magnitude of $+11.05,$ compared to Alpha Centauri A's magnitude of $-0.01 .$ How much more luminous is Alpha Centauri A than Proxima Centauri?

Jill Tolbert
Jill Tolbert
Numerade Educator