Hale Telescope

The 200-inch that held the record for forty-five years, still working on a California mountain, and still the telescope every larger one was measured against.

HistoricPalomar MountainOperational

01 — Interpretation

What these numbers mean

Aperture5.1 m (200 inches)

Twenty-five times the diameter of an 8-inch Dobsonian, and about 630 times its light grasp. Modest beside Keck — and it held the title of largest effective telescope in the world until 1993, which is to say that for most of the twentieth century this was the deepest view humanity had.

MountEquatorial

The only equatorial mount among the great telescopes on this site. Every modern giant is altazimuth, because a computer can drive two axes at varying rates. Before that was possible, a telescope had to be tilted to Earth's axis so a single constant motion could track the sky — which is why this one is built around a 530-ton steel horseshoe.

02 — Specifications

The instrument

Aperture: 5100
Focal ratio: f/3.3
Optical design: Prime focus / Cassegrain reflector, single 200-inch Pyrex mirror
Mount: Equatorial (steel horseshoe)
Mass: 481000

03 — Mission

The observatory

First light: 1949-01-26
Status: Operational
Operator: California Institute of Technology
Site: Palomar Mountain, California
Instruments: Prime focus and Cassegrain instrumentation; adaptive optics

04 — Scale

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.

Hale Telescope5100 mm

Sky-Watcher Flextube 350P SynScan GoTo Collapsible Dobsonian355 mm · 14× smaller

Sky-Watcher Flextube 300P SynScan GoTo Collapsible Dobsonian305 mm · 17× smaller

Celestron StarSense Explorer 12" Dobsonian305 mm · 17× smaller

05 — Context

Twenty years to make one mirror

The 200-inch disc was cast by Corning in 1934, from Pyrex, after an earlier attempt in fused quartz failed and a first Pyrex pour cracked. The blank then cooled for eight months, travelled across the country by rail at restricted speed, and was ground for over a decade — interrupted by the Second World War, during which the optical shop turned to military work.

The finished mirror weighs 13 tonnes and is carried in a telescope of 481 tonnes. It was dedicated in June 1948, and Edwin Hubble took the first official photographs with it in January 1949.

The scale of that effort is the point. A telescope this size was, at the time, one of the largest precision objects ever attempted, and its twenty-year gestation is why the record stood so long. Nobody could simply build a bigger one.

06 — Context

Still working, and you can visit

The Hale is not a monument. It observes, with modern instrumentation and adaptive optics that its designers could not have imagined, and it does useful work on a mountain within a few hours' drive of Los Angeles.

It is also, unusually for the telescopes on this page, somewhere you can go. Palomar has a visitor gallery from which the instrument is visible — an ordinary member of the public can stand and look at the telescope that defined the limit of the observable universe for two generations.

That accessibility is why the Hale sits at the boundary of this collection. The other instruments here are things you read about. This one you can drive to.

Sources

Where these numbers come from

Caltech Palomar Observatory — The Hale Telescope (200-inch, f/3.3, equatorial, 13 t mirror, 481 t telescope, dedicated 1948, first photos 26 Jan 1949, largest effective until 1993)

Elsewhere

More great telescopes

Vera C. Rubin Observatory8360 mm

An 8.4-metre survey telescope that photographs the entire southern sky every few nights, for ten years, to find what changed.

W. M. Keck Observatory10000 mm

Two ten-metre telescopes whose mirrors are not mirrors at all, but thirty-six hexagons each, held in formation to a fraction of a wavelength.

Very Large Telescope8200 mm

Four 8.2-metre telescopes on a Chilean ridge that can observe separately, or combine their light into one instrument no single mirror could be.

Extremely Large Telescope39000 mm

A 39-metre mirror being assembled on a Chilean mountaintop from 798 hexagons — larger than every other optical telescope on Earth combined.

Gran Telescopio Canarias10400 mm

The largest single optical aperture working anywhere on Earth — 10.4 metres of mirror on a volcanic ridge above the Atlantic.

Arecibo Observatory305000 mm

A 305-metre dish built into a Puerto Rican sinkhole that could not point at anything — and, for fifty-seven years, heard more than anything else on Earth.

Atacama Large Millimeter/submillimeter Array

Sixty-six antennas on a plateau five kilometres above sea level, which together resolve detail as a single dish sixteen kilometres wide would.

All ground telescopes →