Analemma: A characteristic figure eight diagram that arises when one plots the Equation of Time versus the declination of the sun. An analemma for Bloomington, Indiana is shown in figure 4.

Equation of Time: The difference between mean solar time and true solar time when located on the reference longitude of the time zone considered.

Gnomon: A ``stick'' on a sundial that casts a shadow on the face of the sundial. The postion and/or length of the shadow gives the time and date.

Local Noon: Time when the sun is found on the meridian. This is observed as the time when the sun is directly south.

Mean Solar Time: Time told by a fictitious sun in which the earth is neither tilted on its axis nor moving about the sun in an elliptical orbit. This is the time indicated by a standard clock or wrist watch.

Meridian: An imaginary line that begins on the northern point of the horizon, travels up to the observer's zenith, down to the southern point on the horizon.

Noon Mark: A mark made on a windowsill, a floor, or wall that indicates the local noon. These are sometimes found in historical houses particularly old farm houses. In the days before affordable wrist watches, these marks were the only practical time pieces available.

Reference Longitude of Time Zone: Longitude from which a time zone is based. Bloomington is in the Eastern Standard Time Zone which is -5 hours from the Greenwich Time Zone. To get the Reference Longitude for the Eastern Time Zone, you take -5 and multiply by to get . Thus the Reference Longitude for the Eastern Time Zone is West longitude.

True Solar Time: Time deterined from actual position of the sun in the sky. This is what sundials actually give. Note: the true solar time is entirely observer dependent. An observer in Bloominton will measure a different true solar time than an observer in Tokyo, Japan. Noon in true solar time is marked by the instance when the sun is located directly south of the observer.

Zenith: An imaginary point located directly overhead of the observer.