Barycentric Julian Day – The current day and time at the center of the Solar System. A Barycenter is the center of mass between two objects. From the combination of Kepler and Newton, we know that objects orbit around a common Focus within an Ellipse. The more massive...

An Ephemeris is an estimation of where/when a particular astronomical event will occur at a particular time in the future. These can be provided in tables, formulas, and graphical depictions. The following will outline examples from Double Stars and Variable Stars.

Here is a loaded question: What time is it? In Astronomy there are a variety of time scales. You will encounter a fair number of them. This video will outline some of these most common ones you will experience.

Epoch is a particular time period, point in history, or a moment defined by a particular event. For Astronomy, it is an arbitrarily fixed instant of time or date. Examples: Planetary orbits, RA & Dec coordinates