Lab 4 (1)
docx
keyboard_arrow_up
School
Purdue University, Northwest *
*We aren’t endorsed by this school
Course
264
Subject
Astronomy
Date
Apr 3, 2024
Type
docx
Pages
4
Uploaded by AdmiralDiscovery11970
ASTR 264
LAB ACTIVITY 4: Stars
Part 1 – Properties of Stars
1. To measure the true brightness (luminosity) of a star, we first need to measure its distance. The method of parallax is useful for determining distances to close-by stars. In the figures
1
below, a set of “stars” has been imaged over the course of six months.
a. Find the star that is moving, or “exhibiting parallax.” Darken this star on each image.
1
adapted from an activity in “Lecture-Tutorials for Introductory Astronomy” by Prather, Slater, Adams, Brissenden
ASTR 264
Lab 4
b. Again, darken
the parallax star in the image for July 2000 below. Also, carefully draw
in the position of the star in January 2001.
c. Using a ruler, measure the distance between Star A and Star B: ______7.5__________ cm
d. Now measure the distance between the positions of the parallax star in July and January: ________4_________ cm
e. A colleague has told you that the angle separating Star A from Star B on the sky is 0.5 arcseconds. Using proportions, determine the angle separating the July and January positions of the parallax star. Show your work.
Star A from Star B on the sky is 0.5 arcseconds. This angle can be used as A. Then we use the information of knowing that the parallax angle is half of the angle separating Star A from Star B.
______ A= 0.5__________________ arcseconds
Now, divide this angle by 2 to get the parallax angle (think about why this is necessary).
Parallax angle =
__________ A/2______________ arcseconds
f. Using the parallax equation, find the distance (in light-years) to the star. Show your work.
Parallax angle= 0.5 sec
Thus
Distance= 1/0.5
= 2
= 2 x 3.26 Ly
=6.52
6.52 light-years
g. Is the parallax star actually moving? Explain what is happening that causes the star to exhibit parallax.
Yes, it seems to be moving moving. A close star will appear to move against the more distant background
stars as the Earth circles the Sun. Astronomers compute the apparent shift in position by measuring a star's location once and then again six months later. Stellar parallax is the apparent motion of a star.
Distant Stars
Parallax Star
Star A
Star B
ASTR 264
Lab 4
h. In the figure below (not to scale!), we see a view from space. The Earth is shown in two positions in its orbit around the Sun: July and January. Label these positions on the figure to match the observations above (not necessarily what was illustrated in the lecture).
i. Suppose the parallax star were slightly farther
from the Earth. Would its parallax motion be more
or less
than the original star’s motion? Explain
.
The distance to the star is inversely proportional to the parallax, Thus, the distance is shorter, the parallax would be larger, and if the distance is farther, the parallax would be smaller.
2. As seen from Earth, two stars appear to have the same brightness
and color
.
a. Do the stars have the same surface temperature? Explain
.
No, the stars do not (necessarily) have the same surface temperature. The apparent brightness and color of a star as seen from Earth depends on various factors, such as the star's distance from Earth, size, and composition. Thus two can look the same but have different surface temperatures.
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
ASTR 264
Lab 4
b. Do the stars have the same luminosity? Explain
.
Stars may have the same luminosity if certain factors of the star is the same. This incudes factors like temperature and size.
3. a. Suppose you traveled to Jupiter, which is about 5 AU from the Sun. Should the apparent brightness of the Sun be more
or less
than what is measured on Earth? Explain
.
Less.
Since Jupiter is farther from the Sun, the apparent brightness would be less. b. If you calculated the luminosity of the Sun, based on your observations near Jupiter, would your result be any different than the luminosity you would’ve calculated on Earth? Explain.
No, luminosity will not change, because luminosity is not observer dependent.
c. Clearly explain the difference between luminosity and apparent brightness.\
Luminosity is a measure of the energy radiated by an object (star). For the stars of the main sequence,
luminosity is directly related to their temperature - the hotter a star is, the more luminous it is. Radius is also important, the higher the radius of an object, for the same temperature, it would have a higher luminosity.
As states earlier, since these variables, Radius, Temperature, and Absolute magnitude, are not observer dependent, Luminosity does not change depending on your location.
Apparent brightness is influenced by distance of the observer to the object. The closer the observer is to the Sun, the greater its apparent brightness. Since Jupiter is farther from the Sun, the apparent brightness would then be less.