Furthermore, contrary to normal intuition, the Theory of Relativity tells us that light always travels at the same speed relative to some observer, no matter what the relative motion of the observer. Thus, light emitted from a moving airplane does not travel with the speed of light plus the speed of the airplane, it travels with the "speed of light", no matter what the speed of the airplane! Although this seems strange, it has been confirmed in many experiments. These experiments show that it is our "common sense" that is wrong in this case!
To be precise, what we usually call the "speed of light" is really the speed of light in a vacuum (the absence of matter). In reality, the speed of light depends on the material that light moves through. Thus, for example, light moves slower in glass than in air, and in both cases the speed is less than in a vacuum. However, the density of matter between the stars is sufficiently low that the actual speed of light through most of interstellar space is essentially the speed it would have through a vacuum, so we don't make much error by ignoring the difference.
For example, Supernova 1987a occurred in a "nearby" galaxy called the Large Magellanic Cloud (adjacent figure). Its light was observed on Earth in 1987, but the distance to the Large Magellanic Cloud is about 190,000 light years. Thus, we normally say that Supernova 1987a occurred in 1987, but it really happened about 190,000 years earlier; only in 1987 did the light of the explosion reach the Earth! If we want to know what the Large Magellanic Cloud looks like "now", we will have to wait 190,000 years.
In comparison, the Sun is only about 8 light-minutes away. So the light we see from the Sun represents what the Sun looked like 8 minutes ago, and we must wait another 8 minutes to see what it looks like "now".
Until recently, the most distant objects were quasars. Now however, examination of the Hubble Deep Field has revealed galaxies that may be further away than the most distant quasars (Ref). The image adjacent left shows what may be the most distant object yet observed. It is the faint red smudge at the tip of the arrow, and appears to be a galaxy further away than any quasar (Ref). If the indirect method of estimating their distance is reliable, at least six galaxies (including the one in the adjacent image) may be so far away that we are seeing them when the Universe was less than 1 billion years old. If so, this implies that the formation of galaxies started relatively soon after the big bang.
Here four filters have been used on the Hubble Space Telescope to emphasize progressively shorter
wavelength light from right to left in the four images. The galaxy indicated by the arrow is only
seen easily in the near IR region of the spectrum, indicating that it has a very large redshift and
therefore is distant.