Open:\
Your assignment document with the information you recorded.\
Open: <https://in-the-sky.org/ephemeris.php?iph=1&ias=1&objtype=1&objpl=Jupiter&objtxt=Jupiter&tz=1&startday=4&startmonth=4&startyear=2023&interval=2&rows=25>

Check that you have the date and time for the image of the planet you are looking up.

Switch to tab "Ephemeris for Jupiter - [In-The-Sky.org](http://In-The-Sky.org)"

Click the planet dropdown and select your planet.

Mercury
Venus
Moon
Sun
Mars
Jupiter
Saturn
Uranus
Neptune

Select "Show angular size"\
Deselect all the other display options.

Switch tabs and look up the date on your own table.

Switch tabs back to in-the-sky.\
Set the start date to match your data.

Switch tabs back to your assignment document.\
Look up the UTC time when your image was taken.

Switch tabs back to in-the-sky and use the table to look that time up.\
Find the UTC time that is the closest to when your image was taken.

Take the Ang. Diam. (") number that corresponds with the closest UTC time.

Switch tabs back to your assignment document.

Enter your Measured Angular Diameter on the Angular Diameter Accuracy table.\
Enter the value you looked up for True Angular Diameter on the table.

Now you will calculate the percent error. If you need a tool for that, follow the next couple steps.

Enter your measurement and true value information into a calculator, such as <https://www.desmos.com/scientific>

Enter that answer in the "Percent Error" column.

In-The-Sky

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How to Check Angular Diameter Accuracy