I’ve only just recently heard of the concept of a light cone, one of many interesting facts I’ve learnt whilst reading Impossibility by John Barrow.
You can visualise it as a simple X-Y graph. The X-axis is space and the Y-axis is time. Any given point in space-time has both a past and a future light cone.
A past light cone represents the space from which light can be received at a given point in space-time. The future light cone represents the space that will eventually be filled by light emitted at that point.
Light cones are described in Impossibility because Barrow observes that the visible universe is described by just such a light cone. The inflationary universe hypothesis means that the actual universe is much larger but we can never get to see it, as our horizon is only expanding at the speed of light. All our observations of the universe are limited to those phenomena that are within our light cone and there’s little reason to assume that what we see is representative of the universe as a whole.
Matt Webb’s utility allows you to calculate the light cone starting from your birth date (any date, actually) out to the first 50 light years. Here’s mine, apparently 12 Ophiuchi will be within my lightcone in about three months time.
Makes you wonder what else is out there doesn’t it?