Vera C. Rubin Observatory
An 8.4-metre survey telescope that photographs the entire southern sky every few nights, for ten years, to find what changed.
What these numbers mean
The famous "8.4-metre mirror" is a ring. Its clear aperture is 8.36 m across but hollow to 5.12 m in the middle, so it gathers as much light as a solid 6.67 m mirror would. Against an 8-inch Dobsonian's 203 mm that is still roughly 1,080 times the light — but a third less than the headline number implies, which is why the honest figure is the one worth quoting.
About seven full Moons across, in a single exposure, at the scale of an 8.4-metre telescope. Most big telescopes see a field a fraction of that. This one number is the whole design: Rubin is not built to look hard at one thing, it is built to look at everything, repeatedly.
The instrument
- Aperture
- 8360
- Effective aperture
- 6670
- Optical design
- Three-mirror anastigmat (Paul-Baker derivative)
- Mount
- Altazimuth
The observatory
- First light
- 2025-06-23
- Status
- Operational
- Operator
- NSF / DOE, managed by NOIRLab and SLAC
- Site
- Cerro Pachón, Chile
- Altitude
- 2647
- Instruments
- LSSTCam (3,200 megapixels)
Against your telescope
Aperture is aperture. The same measurement that describes this instrument describes the telescope in your garage — which is the only honest way to feel the difference.
A telescope built to notice change
Almost every large telescope is an appointment instrument. You apply for time, you are granted a few nights, you point at the object you argued for, and you go home. The sky the telescope did not look at that night is simply not recorded.
Rubin inverts that. It photographs the entire visible southern sky every few nights, over and over, for ten years, and gives the images to everyone. Nobody points it. The survey is the instrument.
What this buys is a memory of the sky. If a star brightens, an asteroid drifts, or a supernova appears where there was nothing three nights ago, the comparison is already in hand — because the previous picture was taken, and the one before that. Discoveries that used to require someone to be looking in the right place now require only that something changed.
The telescope is unusually quick for its size. It repositions and settles in a few seconds, because a survey that takes a minute to move between fields would never finish a sky.
The camera, and what ten years of it means
LSSTCam records 3,200 megapixels per exposure — the largest digital camera ever built for astronomy. A single image is so large that displaying one at full resolution would take a wall of several hundred televisions.
The number that matters more is the total. Ten years of repeated imaging produces a record of roughly twenty billion galaxies and twenty billion stars, each one measured hundreds of times. That is not a picture; it is a time series of the observable universe.
The practical consequence for someone reading this from a back garden is that Rubin will find things faster than anyone can follow them up. It is expected to raise the number of known solar system objects by an order of magnitude, and to alert on millions of changes per night. Most of those alerts will never be examined by a human at all.