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 Jupiter's Bright Moons

Recognizing Jupiter's Moons by their Brightness!

November 1, 1999, about 2:20 UT

Four of Jupiter's moons are bright!  They were discovered by Galileo in 1610.

Jupiter's moons are like a mini solar system orbiting Jupiter.  We see the orbiting moons from the side rather than from above or below Jupiter.  So, the moons appear to line up on either side of Jupiter.  Depending on where the moons are in their orbits, they can appear close to or far from Jupiter.

Can we use auto aperture to tell which moon is which?

When you look at Jupiter with a telescope, there are no labels to tell you which moon is which.  Let's see if we can identify the moons by their brightness.

Use auto aperture to find the brightness of each moon.

• Open JupG1999Nov01.fts  This image was taken with a green filter.

• Use the tool auto aperture.   Click on each moon in the image.

•  Brightness Counts for Each Moon  Image: _______________________ Io __________________________ Europa _____________________ Ganymede ___________________ Callisto _____________________

Create a table to record your results.

• Put your data in a new table.  List the moons in order of their brightness, brightest one first.
• Write the magnitudes of the moons as defined by astronomers, in the column next to each moon.  The magnitudes for the moons of Jupiter are:
Io 5.0        Europa 5.3        Ganymede 4.6         Callisto 5.6
• Add a column for the brightness counts.
• Magnitudes with lower numbers indicate brighter objects.
• How does the order of the brightness counts match the order for the magnitude values?

Do the moons keep the same order of brightness when we use different filters?

• Open two more images:  JupR1999Nov01.fts and JupB1999Nov01.fts.
• Create a new data table or extend your previous table.
• Use the auto aperture tool to measure the brightness counts for each moon in each image.
• Does the order of the brightness counts for the four moons stay the same in each filtered image?
• Try this for the V filtered image, JupV1999Nov01.fts.