Explain how light and its physical properties can be used gather information on celestial objects related to 1) composition, 2) temperature, and 3) motion (speed and direction).

The information about the said quantities are obtained as explained under:

1) Composition: The information about the composition of celestial objects is obtained by the spectrum of the light that is obtained when light from these sources is analysed by a spectrometer.The study of such spectra of light is known as spectroscopy.The spectra of the light emitted by any body is a signature of the material that is present in the body as each and every object in this universe has it's unique spectra.

2) The temperature of any celestial object can be obtained by studying the composition of radiation emitted by it. Every object in this universe emit's heat in the form of radiation and the type of radiation emitted by an object depends on it's temperature.Thus if we study the radiation emitted by the objects we can get information about the temperature that the object has.

3)Motion: While travelling in space relative to the observer on earth the light emitted by any celestial object undergoes a shift in the frequencies of the light that it emit's and this phenomenon is known as red shift. By measuring the shift in the light we can deduce speed of the object.

1. Through spectrum

               2. Through wavelength

               3. Through Doppler effect

Explanation:

1 ) Composition : When light passes through celestial objects it gives some pattern on emission and absorption spectrum. As different celestial bodies are made up of different material their spectrum differs from one another thus giving information about their composition.

2) Temperature : The wavelength emitted by each celestial body gives a graph stating the radiation emitted by them. This helps to find the temperature.

3) Motion : Doppler effect very well define the motion of celestial bodies. Wavelengths shifts in this effect and the ratio of wavelengths of shifted to the  non shifted lines gives us information about the motion of celestial bodies.

probably not if net force is zero