Part 1: Finding the Distance to Stars Using
the Parallax Angle
Chapter 15 and Appendix D (pp. 543-545) in the textbook and the background
the three questions at the bottom directly in this lab worksheet.
NASA web page provides additional explanation and allows you to check your
Parallax is the apparent shift in the location of a star due to the orbit of
the Earth. In other words, the star will
appear to be in a different place depending on the line of sight from the
Earth. By knowing the diameter of Earth’s orbit and by measuring the angle of
apparent shift (the parallax angle), astronomers can calculate the distance to
the nearby stars using trigonometry. This method has been used for centuries.
The ancient Greeks were able to measure some of the closest stars this way. Today,
sophisticated telescopes have greatly enhanced this method. Figure 1 is a
graphic from your textbook showing how this works:
this assignment, you will determine the distance to a star, “HT Cas”, using the
method of stellar parallax. Figure 2 and 3 below are photos of HT Case, taken
six months apart:
super-impose these photos, we get the following image (figure 4):
see that the position of the star appears to have changed over the six-month
time period. However, it is actually the
angle from which the photos were taken that has changed. During that 6-month period, the Earth moved
from one side of the sun to the other.
stellar astrometric catalog, we find that the two stars closest to HT Cas are a
distance of 0.01 arcseconds apart. Based on this information, we can estimate
that the angle of shift of HT Cas (the parallax angle) to be approximately
0.015 arcseconds apart.
know that the radius of the Earth’s orbit is 1.0 A.U. (astronomical units).
these two measurements, we can then determine the approximate distance to HT
Cas using the following equation:
d= distance to HT Cas
a=radius of the Earth’s orbit
points) Given the above equation and information provided, about how far away
is HT Cas?
points) Your answer was calculated in parsecs.
Given that 1 parsec = 3.2616light years, about what is the
distance to HT Cas in light years? (Your answer
in parsecs X 3.2616 light years = The Distance to HT Cas in light years).
points) Based on your answer, do you think this is a star that we might be able
to send a space probe to? Why or why
not? Support your answer.
Part 2: Using a Hertzsprung-Russell Diagram
Instructions: After reading the
Unit VIII lesson, clickhere to access the NASA
web page “Stars” and answer the questions below using Figure 5. You can also
copy and paste the web address into your browser:
that the stars in Figure 5 are not uniformly distributed. Rather, about 90
percent of all stars fall along a band that runs from the upper-left corner to
the lower-right corner of the H-R diagram. These “ordinary” stars are called
main-sequence stars. As you can see in Figure 5, the hottest main-sequence
stars are intrinsically the brightest, and, conversely, the coolest are the
dimmest. The absolute magnitude of main-sequence stars is also related to their
mass. The hottest (blue) stars are about 50 times more massive than the Sun,
whereas the coolest (red) stars are only 1/ 10 as massive. Therefore, on the H-R
diagram, the main-sequence stars appear in decreasing order, from hotter, more
massive blue stars to cooler, less massive red stars (Lutgens, Tarbuck, &
Assignment:Use Figure 5 to
answer the questions. Once all questions have been answered for both part 1 and
part 2, save this worksheet with your last name and student number and upload
to Blackboard for grading.
1. (10 points) Main
Sequence stars can be classified according to which characteristics? What are
the characteristics of our Sun?
points) Which main sequence stars can be found with a surface temperature of
between 3000K-4000K? Which stars have a luminosity about 100 times less than
that of the Sun?
points) Briefly describe the solar evolution time-line of a common star like
our own from formation through collapse.