On December 21, 2020, a visual astronomical spectacle will occur. The planets Jupiter and Saturn will pass so close to each other in the sky that, to the unaided eye, they will be difficult to separate. This is the closest the two planets have come in 397 years; the last time they were this close was July 16, 1623. When Jupiter and Saturn come close to each other in the sky as seen from Earth, this is known as a “great conjunction” and happens about every 20 years or so. But not all great conjunctions are as close as this one. The next great conjunction will be on November 5, 2040, and again on April 10, 2060, but the planets will be a bit over a degree apart, so not as close as the 2020 event. The next comparable event will be on March 15, 2080.
Stellar CCD aperture photometry is the technique of extracting information about the brightness of stars from a series of images collected over time. The light curve of a variable star can reveal useful information about the physics of the star, including a measure of its intrinsic brightness. Light curve analysis can yield information about eclipsing binary systems, and also lead to exoplanet discoveries when a planet alters the brightness of a star by crossing its disk as viewed from Earth.
In CCD photometry, we want to be able to determine a measure of the amount of radiation coming from a given star arriving on our CCD detector. Plotted as a function of time, this measurement can reveal important information about the star or star system.