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Pathways to Astronomy

Stephen E. Schneider

Chapter 27

Collecting Light - all with Video Answers

Educators

Chapter Questions

01:19

Problem 1

If you look at stars with binoculars with lenses about $8 \mathrm{cm}$ $(3 \text { inches })$ in diameter, how many times fainter a star should you be able to see compared to what you can see with your unaided, fully dilated eye, with the pupil open to about $8 \mathrm{mm}$ ?

Carlos Henrique De Lima
Carlos Henrique De Lima
Numerade Educator
04:01

Problem 2

Compare the collecting area of one of the 36 segments of the 10.4-meter GTC to the collecting area of the 2.4-meter Hubble Space Telescope. Which is larger? By what factor?

MC
Miles Call
Numerade Educator
02:57

Problem 3

A group of stars is observed through several different filters, and some stars are seen to be brightest when observed through either the $V(500-590 \mathrm{nm})$ or $\mathrm{R}(570-710 \mathrm{nm})$ filter.
a. Assuming a star is brightest in the middle of the $\mathrm{R}$ filter, use Wien's law (Unit 23.4 ) to estimate its temperature.
b. If a star is brightest through the $V$ filter, use Wien's law to estimate the range of temperatures it might have.

Elliott Walker
Elliott Walker
Numerade Educator
02:24

Problem 4

The energy of the light reaching Earth from a "first magnitude" star is approximately $10^{-6}$ watts (joules per second) over each square meter of a telescope's collecting area. Assuming that this light is composed of photons of wavelength $500 \mathrm{nm},$ about how many photons are arriving in a square meter each second? How many photons enter your eye each second if your pupil is $8 m m$ in diameter?

Khoobchandra Agrawal
Khoobchandra Agrawal
Numerade Educator
00:38

Problem 5

At a radio wavelength around $30 \mathrm{cm},$ the Arecibo radio telescope can collect about $3 \times 10^{-14}$ watts (joules per second) of radiation from the Crab Nebula. About how many photons is it collecting each second?

Averell Hause
Averell Hause
Carnegie Mellon University
02:24

Problem 6

The orbiting Chandra X-ray telescope, observing at about $0.1 \mathrm{nm},$ can collect about $2 \times 10^{-13}$ watts (joules per second) of radiation from the Crab Nebula. About how many photons is it collecting each second?

Khoobchandra Agrawal
Khoobchandra Agrawal
Numerade Educator