PHYS 1403 Lab 7: APPARENT & ABSOLUTE VISUAL MAGNITUDE
Worksheet
Enter your answers to each question in the data tables and yellow highlighted areas
below. When completed, please save and upload this file to the assignment – Lab 7 – in
Canvas.
PRELAB QUESTIONS
1. The apparent visual magnitude of Canopus is –0.6 and that of Hadar is +0.6. Which
star is brighter? How do you know?
The Canopus star would be brighter than Hadar. This is because after professional
research done by astronomers, it has been concluded that the smaller the
apparent visual magnitude, the brighter the star. Therefore, compared to the
apparent visual magnitude of Hadar which is +0.6, Canopus is brighter with an
apparent visual magnitude of -0.6.
2. What is the absolute visual magnitude of a star?
The absolute visual magnitude of a star is 10 parsecs or 3.26 light years.
3. Epsilon Eridani has an apparent visual magnitude of + 3.7. Will it will be visible with
the naked eye? How do you know?
Epsilon Eridani has an apparent visual magnitude of +3.7, which will be visible with the
naked eye. This is because any object with an apparent magnitude of 6 or less
can be visible with an unaided eye.
4. Ross 128 has an apparent visual magnitude of +11.1. Will it will be visible with the
naked eye? How do you know?
Ross 128 has an apparent visual magnitude of +11.1, which will not be visible with the
naked eye. This is because any magnitude that is 6 or less is visible to the unaided eye
and since the apparent visual magnitude of Ross 128 is greater than 6, it will not be
visible with the naked eye.
5. Ross 128 is 3.4 parsecs from us. If it were moved to 10 parsecs, would it appear
brighter or dimmer? Why?
Ross 128 is 3.4 parsecs away from the Earth and if it were moved 10 parsecs away, it
would be further away from the Earth. This would cause Ross 128 to appear dimmer
!1
, because the magnitude is an inverse scale. Therefore smaller magnitudes equal
brighter stars. Because the the magnitude becomes higher, the star becomes dimmer.
EXERCISE
In this lab, we will use Stellarium find information about individual stars. First, you will
need to start the program. After the program has started, move your cursor to the left
side of your screen to bring up the vertical menu, and click the “Sky and viewing options
window” icon. Click the “Sky” tab, and un-check the box that says “Show atmosphere”.
Daylight should fade and stars should now be visible (although the sun may still be
displayed in the sky). You can move around by simply clicking on the screen and
moving the mouse. We also need to remove the ground from the screen. To do this,
open the Sky and viewing options window again, and click on the “Landscape” tab.
Now, un-check the boxes labeled “Show ground” and “Show fog”. This should remove
the ground from the screen. Close the Sky and viewing options window, and now you
are ready to start the exercise.
Part A – Collect, manipulate, graph, and analyze data. Use analysis to evaluate a
hypothesis.
Let’s test a hypothesis suggested by a know-it-all friend. You know from your
studies in Astronomy that this hypothesis is not correct, but you have the task of
convincing your friend. Your friend insists on the Hypothesis that: “A star is a star.
All stars have the same intrinsic brightness. The reason why they appear to have
different magnitudes is because they are at different distances from the Earth.
This means a star close to the Earth will always be brighter than a star far away.
Therefore, knowing the apparent visual magnitude of a star tells you the distance
that star is from the Earth.”
1) Below in Data Table 1 is a list of 22 of the brightest stars in the night sky. To
test your friend’s hypothesis, we will use Stellarium to gather information on
this group of stars. First, open the “Search window” from the vertical menu on
the left side of the screen. To find an object, simple type the name of the
object in the box, and press “Enter” on your keyboard. Stellarium will
automatically move your view over to that object. The first star in Data Table 1
is Sirius. Type this star name in the box in the Search window and press
“Enter”. Stellarium should now move to Sirius. Information on this object is
displayed in the upper left corner of the screen. Use this method to find and
record the distance, apparent magnitude mv (Stellarium refers to this as just
“Magnitude”), and absolute magnitude Mv for each star in Data Table 1 –
stars Sirius and Spica have been entered and calculated for you as
examples. Calculate the distance in Parsecs (pc) using the conversion: 1 pc =
!2
Worksheet
Enter your answers to each question in the data tables and yellow highlighted areas
below. When completed, please save and upload this file to the assignment – Lab 7 – in
Canvas.
PRELAB QUESTIONS
1. The apparent visual magnitude of Canopus is –0.6 and that of Hadar is +0.6. Which
star is brighter? How do you know?
The Canopus star would be brighter than Hadar. This is because after professional
research done by astronomers, it has been concluded that the smaller the
apparent visual magnitude, the brighter the star. Therefore, compared to the
apparent visual magnitude of Hadar which is +0.6, Canopus is brighter with an
apparent visual magnitude of -0.6.
2. What is the absolute visual magnitude of a star?
The absolute visual magnitude of a star is 10 parsecs or 3.26 light years.
3. Epsilon Eridani has an apparent visual magnitude of + 3.7. Will it will be visible with
the naked eye? How do you know?
Epsilon Eridani has an apparent visual magnitude of +3.7, which will be visible with the
naked eye. This is because any object with an apparent magnitude of 6 or less
can be visible with an unaided eye.
4. Ross 128 has an apparent visual magnitude of +11.1. Will it will be visible with the
naked eye? How do you know?
Ross 128 has an apparent visual magnitude of +11.1, which will not be visible with the
naked eye. This is because any magnitude that is 6 or less is visible to the unaided eye
and since the apparent visual magnitude of Ross 128 is greater than 6, it will not be
visible with the naked eye.
5. Ross 128 is 3.4 parsecs from us. If it were moved to 10 parsecs, would it appear
brighter or dimmer? Why?
Ross 128 is 3.4 parsecs away from the Earth and if it were moved 10 parsecs away, it
would be further away from the Earth. This would cause Ross 128 to appear dimmer
!1
, because the magnitude is an inverse scale. Therefore smaller magnitudes equal
brighter stars. Because the the magnitude becomes higher, the star becomes dimmer.
EXERCISE
In this lab, we will use Stellarium find information about individual stars. First, you will
need to start the program. After the program has started, move your cursor to the left
side of your screen to bring up the vertical menu, and click the “Sky and viewing options
window” icon. Click the “Sky” tab, and un-check the box that says “Show atmosphere”.
Daylight should fade and stars should now be visible (although the sun may still be
displayed in the sky). You can move around by simply clicking on the screen and
moving the mouse. We also need to remove the ground from the screen. To do this,
open the Sky and viewing options window again, and click on the “Landscape” tab.
Now, un-check the boxes labeled “Show ground” and “Show fog”. This should remove
the ground from the screen. Close the Sky and viewing options window, and now you
are ready to start the exercise.
Part A – Collect, manipulate, graph, and analyze data. Use analysis to evaluate a
hypothesis.
Let’s test a hypothesis suggested by a know-it-all friend. You know from your
studies in Astronomy that this hypothesis is not correct, but you have the task of
convincing your friend. Your friend insists on the Hypothesis that: “A star is a star.
All stars have the same intrinsic brightness. The reason why they appear to have
different magnitudes is because they are at different distances from the Earth.
This means a star close to the Earth will always be brighter than a star far away.
Therefore, knowing the apparent visual magnitude of a star tells you the distance
that star is from the Earth.”
1) Below in Data Table 1 is a list of 22 of the brightest stars in the night sky. To
test your friend’s hypothesis, we will use Stellarium to gather information on
this group of stars. First, open the “Search window” from the vertical menu on
the left side of the screen. To find an object, simple type the name of the
object in the box, and press “Enter” on your keyboard. Stellarium will
automatically move your view over to that object. The first star in Data Table 1
is Sirius. Type this star name in the box in the Search window and press
“Enter”. Stellarium should now move to Sirius. Information on this object is
displayed in the upper left corner of the screen. Use this method to find and
record the distance, apparent magnitude mv (Stellarium refers to this as just
“Magnitude”), and absolute magnitude Mv for each star in Data Table 1 –
stars Sirius and Spica have been entered and calculated for you as
examples. Calculate the distance in Parsecs (pc) using the conversion: 1 pc =
!2
