The Mean Solar Day

Objectives: Timekeeping on Earth is loosely based on the position of the Sun in the sky. Apparent solar time is the time like a Sundial would tell, where local noon is when the Sun would be directly to the South. However the length of the apparent solar day is not constant throughout the year because of two contributing factors. To account for these varitions the solar day is averaged so all the days of the year will be of equal length. Mean solar time is the time that clocks display. The difference between apparent solar time and mean solar time is called the equation of time.

The Clock We Live On, Isaac Asimov

The apparent solar day may only gain or loose as much as 20 seconds per day, but the difference adds up because the effects are cumulative. For instance, if the apparent solar day is longer than the mean solar day today, then the Sun will rise at a later time tomorrow. This project will measure the equation of time for your location on a given day. We will publish the plotted data that is sent back to us. A curve close to that of the equation of time should become evident as we receive more project results.

Project setup:

You should complete the Finding North project to get a North-South line. The stick or pole that you use to make the shadow for the North-South line should be placed in a permanent position for this project. A clock that is set to Universal Time from the

Please record the following information:
Click on the submit button when through.

The UT and date when the Sun crossed the North/South line:

The name of your town or city and state

The name of your town or city and state

Your longitude in degrees and minutes :

Your E-Mail address:

Any additional comments: