Question

how can we be certain the EM wave we receive from space tell us all about the composition and the source temperature why, or why not?

How the location and dynamics of celestial objects affect the observation of space?

Answer 1

The em wave which we are receiving from the celestial object then there is some absorption and emissions line of different metals, which were present in the object. Identify that lines we can say the object is composed of this metal and etc.

Again when the em wave is received, it follow the black body radiation curve, whose peak is at the surface Temperature of that celestial object from which it is origeneted.

The visibility of space objects

The apparent brightness and probability of detection of objects in space depend upon the following important factors, each of which must be specified in order to estimate the visibility accurately:

• The object's physical characteristics: size, shape, surface texture, color (if visible only by reflected light), or luminosity and spectral nature (if self-luminous) .

  The distance between object and observer.

  The brightness and character of the backgrounds or field against which the object is being observed.

  The visual acuity of the observer and the magnifying power of his optical aids (if any ) .

  The spectral absorption characteristics and the light-transmitting ability of the medium between object and observer.

  The apparent motion of the object, and the change in its appearance as a function of time (whether steady, flickering, flashing, etc. ) .

In normal experience, we are compelled to view extraterrestrial objects through the Earth's atmosphere, which scatters light, is often cloudy, and is in constant motion. The movement of the atmosphere, even in the clearest weather, imposes a severe limit on the resolving power of large telescopes (their ability to produce finely detailed images or photographs). Thus, a large telescope employed above the atmosphere-say, on the surface of the Moon-would have a greatly enhanced ability to resolve details on the surfaces of the planets and the Sun and would tremendously improve man's ability to explore the entire visible universe.

The factors influencing the visibility of objects in space, listed above, are quite obvious and well recognized in ordinary everyday experience. However, to take them all into account simultaneously in calculating the visibility of distant objects usually becomes quite involved. Since simple mathematical expressions which would be useful under a wide variety of conditions cannot be formulated, a number of examples are given below to illustrate some size-distance relationships in the detection of just barely visible objects.