Atlas of Nearby Stars: Projects in Virtual Astronomy

Sirius A Parallax

FIGURE 15. Sirius A Parallax

 

Figure 15 is a screen grab from the running applet. To try this virtual experiment, select the ATLAS icon to start the applet.

 

See the list of other virtual experiments.

 

VIRTUAL EXPERIMENT 7
Calculating Absolute Magnitude for Sirius A

EDUCATIONAL OBJECTIVES

INSTRUCTIONS

  • Set the selected target star to Sirius A.

  • Calculate the distance to Sirius A using the method outlined in experiment 4.

  • Note the apparent magnitude and spectral type of Sirius A as noted in the data window.

  • Use the Apparent Magnitude and calculated distance for Sirius A to determine the Absolute Magnitude using Equation 6.

  • Plot the location of Sirius A on an H-R diagram.

WHAT TO OBSERVE OR NOTE

  • Some advanced amateur astronomers can roughly estimate apparent magnitude by looking at a star in the night sky.

  • Accurate measurements require a photometer or a CCD camera telescope attachment.

  • Parallax measurement mode scales the size of the star, based on its apparent magnitude from earth. Note that Perspective project mode scales it relative to the apparent magnitude as observed from deep space.
HR Diagram for Sirius A

Figure 16. A screen shot showing the HR Diagram for Sirius A.

 

In Figure 15, the parallax angle for Sirius A is measured to be 0.38 arc seconds. Applying Equation 3, the distance to Sirius A is therefore:

Distance calculation

The Apparent Magnitude is found to be -1.44. Using Equation 6, the Absolute Magnitude of Sirius A is therefore:

Absolute Mag calculation

Knowing that Sirius A is of Spectral type A1, with an absolute Magnitude of 1.46 allows the star to be accurately positioned on the HR diagram, as shown in Figure 16.