Determining the size of space objects

Determining the size of space objects – If the dimensions of a space object can be measured, and its distance to another object is also known, then to determine the linear size it is necessary to solve the simplest geometric problem. Thus, the sizes of the Sun, planets, their satellites, star systems, galaxies, nebulae and other objects were determined. Based on this method, the sizes of a relatively small number of the closest and largest stars were calculated. Because of their peculiarities, their angular size was determined using special methods that include interferometers and analysis of the nature of light diffraction that occurs when these stars are covered by the Moon.
Another method is used to determine the size of the large majority of stars with very small angular dimensions, which means that they cannot be measured. It consists in the fact that the luminosity of a star can be determined by the known distance to the star and its apparent magnitude. Further, if you know its temperature and assume the presence of radiation in the form of a black star (in this case, the radiation flux from it is directly related to its temperature), then you can calculate the surface area of the star required for this flux, as well as its diameter.
Also, by analyzing the brightness curve of an eclipsing variable star, it is easy to determine the relative sizes of its two component stars, which alternately obscure each other.