pre-lab 6.pdf dalila
pdf
keyboard_arrow_up
School
University of California, Los Angeles *
*We aren’t endorsed by this school
Course
3
Subject
Astronomy
Date
Dec 6, 2023
Type
Pages
2
Uploaded by ElderBook3640
Pre-Lab 6
Name
ID#
Section
Stars, Spectra, and the H-R Diagram Pre-lab
Hand in this pre-lab at the beginning of the Stars, Spectra, and the H-R Diagram Lab.
Much of what we know about the Universe is based on what we know about stars. Our
knowledge of light and spectra enables us to study the properties of stars without being able
to visit them directly.
In this lab, we’ll look at how we use the information contained in
starlight to determine their sizes, temperatures, distances and luminosities.
Relationship Between Luminosity, Distance, and Brightness
The luminosity of a star is the amount of energy a star gives o
↵
each second.
The
brightness is the amount of that energy that reaches Earth.
Before jumping into the
luminosity and brightness of stars, let’s start with an analogy that is more down to earth.
1)
You are standing near a road at night. You see a person with a flashlight in hand walking
towards you. As the person approaches you, does the flashlight appear brighter or dimmer
than it was when the person was far away?
2)
Does the total amount of light emitted by the flashlight (i.e., the luminosity of the
flashlight) change as the person approaches you? Why or why not?
Continues on next page
!
1
3)
An
intrinsic
property is a fundamental property that does not depend on the observer.
With the previous two answers in mind, is luminosity an intrinsic property of a light
source or does it depend upon the observer? How about
apparent brightness
?
In this analogy, the flashlight represents a star. Astronomers often measure the brightness
of a star in order to determine more useful information about the star: its luminosity and
distance. How bright a star appears to observers on Earth depends on both its luminosity
and distance.
4)
Imagine that you look at the night sky and see two stars of equal brightness. Can you be
sure that they have the same luminosity? Why or why not?
The relationship between a star’s luminosity and brightness is described by the
inverse
square law
:
B
/
L
d
2
Or, in words :
Brightness
/
Luminosity
(distance)
2
(4)
5)
Let’s use this expression to solve a problem. Star X and Star Y are intrinsically identical
stars. If Star X is located 20 light-years from Earth and Star Y is located 40 light-years
from Earth, what is the ratio of their apparent brightnesses,
B
StarX
B
StarY
?
Show your work
below.
End of Pre-Lab 6
2
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help