A Recent report about a cosmic burst 3.8 billion light years away. It is written as though it is happening now. However, my question is, if the event is 3.8 billion light years away, doesn't that mean we are continuously looking at history, or is it possible to detect activity in "realtime" despite the distance?

  • $\begingroup$ Even for stuff as close as the sun, we qualify observations of it as 'near real time' (NRT), as there's lag from reading out the CCD, pipeline processing, etc. $\endgroup$ – Joe Jun 3 '11 at 6:00

You are absolutely correct. The event happened 3.8 billion years ago, but it gets tedious and confusing to write in the past tense. For example, which one of the following statements do you find easier to understand?

The high-energy radiation continued to brighten and fade for at least a week after the burst 3.8 billion years ago


More than a week later, high-energy radiation continues to brighten and fade from its location

As an example, see this article about writing in astronomy, under Miscellaneous Sticky Points:

Remember that statements about astronomical objects should always be in present tense ("the galaxy has a strong color gradient") unless you are specifically talking about a past event or an object that no longer exists ("the supernova progenitor star was a type O supergiant").

Hope that helps.


From Wikipedia:

The finite speed of light is important in astronomy. Due to the vast distances involved, it can take a very long time for light to travel from its source to Earth. For example, it has taken 13 billion (13×109) years for light to travel to Earth from the faraway galaxies viewed in the Hubble Ultra Deep Field images. Those photographs, taken today, capture images of the galaxies as they appeared 13 billion years ago, when the universe was less than a billion years old. The fact that more distant objects appear to be younger, due to the finite speed of light, allows astronomers to infer the evolution of stars, of galaxies, and of the universe itself.

So this means that you actually see what happened a long time ago if it is very far away.


This is true, but you should not forget that comparison of times depends on the frame of reference by relativity theory. In particular, from the point of view of the travelling light, no time has passed.

You might want to look at the cartoon at


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