The Limit Of What Hubble Can See
The most powerful telescope in history will never see the farthest galaxy.
“No distance of place or lapse of time can lessen the friendship of those who are thoroughly persuaded of each other’s worth.” -Robert Southey
With all that the Hubble Space Telescope has done — including staring at a blank patch of sky for weeks worth of time — you might think there’s no limit to how far it can see. After all, what appears to be dark, empty space is illuminated by the light from thousands upon thousands of galaxies, leading to the conclusion that there are hundreds of billions of them out there spanning the entire sky.
In fact, some of these galaxies are so faint and distant that Hubble can barely see them. But what might surprise you is that there are two reasons Hubble’s limited in what you can see, one reason that’s obvious and one reason that’s much more subtle.
- Obviously: Hubble “only” has a 2.4 meter diameter mirror, meaning it can only gather as much light — as many photons — as that mirror can collect. Even over 23 days, the longest exposure of a region ever taken, that only enables it to see very bright galaxies at the greatest distances.
