CCD cameras are composed of silicon chips that are sensitive to light, changing detected photons of light into electronic signals that can then be used to make images of astronomical objects or to analyze how much light is being received from such objects.
Note that those careless people (notably dealing with variable stars) who use a less-than sign ( the specified magnitude, because a smaller number in astronomical magnitudes means ; if they wish to use a mathematical symbol to denote limiting magnitude, the only proper option is to use a sign, >, but this alone does not tell the reader whether the object was visible (and somewhat fainter than the specified value) or invisible.
Change - definition of change by The Free Dictionary
The JD is always half a day off from Universal Time, because the current definition of JD was introduced when the astronomical day was defined to start at noon (prior to 1925) instead of midnight.
Physics + Astronomy | University of Wisconsin-Eau Claire
Bessel introduced a system whereby it would be convenient to identify any instant of time by giving the year and the decimal fraction of the year to a few places, but the starting time of the year was not convenient for dynamical studies that utilize Julian dates (see definition for Julian date), differing by 0.5 day, and the Besselian year varies slowly.