During the first year of its operation, only 20% of the projects scheduled for the Hubble Space Telescope involved taking images and pictures of celestial objects. The remaining 80% of the telescope's time was devoted to observing the spectrum of celestial objects. Why do astronomers place such a high emphasis on looking at the spectrum of a celestial object rather than an image? Explain

Question

What will be an ideal response?

Answer 1

Some important information about the shape, size and physical nature of an object can be determined from an image. The analysis of an object's spectrum can yield more important information, even if the object is too small or distant for any shape or size to be determined.

Using Wien's law, a continuous or absorption spectrum can be used to find the surface temperature of an object based purely on the pattern of energy emitted at different wavelengths.

The position of spectral lines in an absorption or emission spectrum is a reliable way to identify chemical elements that are present in or around the object. In some cases, the relative amount of the different elements can also be determined.

If the pattern of spectral lines is shifted from what is expected as a result of the Doppler effect, the motion of the object toward, or away from the observer can be determined.

All of these things can be determined simply by looking at the distribution of photons of different wavelengths coming from an object - the object's spectrum. Since the photons travel to the observer, it is not necessary for the observer to travel to the source for these observations. This is a great advantage, since astronomical distances are too large to permit travel to the objects themselves.