The star is a congestion of the heated gases, usually hydrogen and helium which radiates light and heat thanks to the nuclear and thermonuclear reactions happening in it. The closest to us a star the Sun, the star, next to our solar system, is at distance of 4.5 light years (distance which passes light for 1 year) from Earth. To terrestrial measures it is huge figure.
The mankind was engaged in studying stars since the most ancient times. Results of researches were used for navigation of sailors and definition of time. Until recently the simplest telescopes which allowed to watch stars were the main tool of astronomers. Today in studying stars besides ordinary optical telescopes radio telescopes which register not visible light of a star, and the electromagnetic radiation proceeding from it are used. The radio telescope allows to investigate the stars which are at distance is much bigger, than a striking distance of optical telescopes.
Separately It should be noted the orbital Hubble telescope which allowed to conduct observations which were not prevented by the atmosphere of Earth and adverse weather conditions.
Besides optical and radio telescopes the astronomers use special photography equipment which photographs big sites of the star sky with great patience for examining of stars. The great patience allows radiation to collect from weak stars that does them further visible in pictures. Photos are used then for search of new stars which cannot be found in other ways as their radiation too weak. Other very important way of studying stars is the spectral analysis. Scientists can determine temperature on star surfaces, the chemical composition of substance of a star and the nature of its movements in the Universe by the spectral analysis. All stars are divided on spectral classes, stars of one class have one color. This color can vary from red to blue. Star temperature depends on color of a range: the hottest stars blue, temperature of their surface begins from 25000 degrees, red stars the coldest, their temperature usually does not exceed 1600 degrees. It is possible to define availability of any given chemical element in a star having compared an element range to parts of a range of a star. Helium and hydrogen, elements of which stars consist meet also on Earth.