A teasing radiance
John H Friday 28th March, AD 2008
I was fascinated by today’s Astronomy Picture of the Day, which depicts what is almost certainly the most distant object ever seen by the naked eye – but only if someone’s naked eye happened to be looking at the right part of the sky at the right moment on 19 March 2008.
Normally the most distant object visible with the naked eye is the Andromeda Galaxy, at about 2.5 million light years from earth. However, on 19 March a gamma-ray burst was briefly visible in the constellation Bootes, as shown in the left-hand image above. It turns out that the object which produced this burst was 7.5 billion light years from earth, making it both the intrinsically brightest object ever seen (2.5 million times brighter than the brightest known supernova) and the most distant object capable of being seen with the unaided eye.
Of course, very few people are likely to have witnessed this brief but momentous event, and probably no-one would have appreciated its significance at the time if they had happened to notice this brief, faint glow. You have to feel sorry for all those photons: they spend 7.5 billion years crossing the universe, and then whack into the earth’s surface without anyone noticing them.
When I mentioned this to my wife, she drew my attention to this wonderful and highly apposite poem by Elizabeth Jennings:
Delay
The radiance of that star that leans on me
Was shining years ago. The light that now
Glitters up there my eye may never see,
And so the time lag teases me with howLove that loves now may not reach me until
Its first desire is spent. The star’s impulse
Must wait for eyes to claim it beautiful
And love arrived may find us somewhere else.
Yes, that was it.
[...] John Halton is similarly fascinated by light that is seven and a half billion years old: [...]