A table of definitions and usage of thingies that are marked with an asterisk (*).

Keyword	Abbreviation for	Description	Use
Sgr A*	Sagittarius A*	A region in the middle of the Milky Way (our galaxy). It's believed that a supermassive blackhole lives there.	Celestial bodies that orbit the center of the Milky Way
R☉	Solar Radius	The solar radius is self-explanatory as its name reveals everything it's about. R☉ is a unit of length and its value is approximately 695 500 km (6.955 x 108 metres).	Expressing the size of stars
Au	Astronomical Unit	A unit of length in which the exact value is 149 597 870 700 metres and is the mean distance between the Earth and the Sun.	Measurement of long distances in outer space
K	Kelvin	An absolute temperature scale. Unlike the Celius and the Fahrenheit scales, no negative values are present here. Formulae: [°C] = [K] − 273.15 [°F] = [K] × 9⁄5 − 459.67	Measurement of temperatures in outer space