1920s 1930s 1940s 1950s 1960s 1970s 1980s 1990s 2000s 2010s

18-inch operational

48-inch operational

200-inch operational

60-inch operational

PTI operational

Rockefeller grant awarded

June 1928:

Rockefeller Grant Awarded

George E. Hale received assurance of funding from the Rockefeller Founda­tion to start building the 200-inch telescope.

site selection

1929 – 1934:

Site Selection

Several candidate sites for the future observa­tory were surveyed for their seeing conditions using 4-inch refracting telescopes.

shops built

1931 – 1933:

Shops Completed

The Caltech optical and instrument shops were built to support the figuring of the 200-inch mirror and other optical elements, as well as the fabrica­tion of auxiliary equipment. The Astro­physics Laboratory (Robinson) was also completed in 1931.

site construction

Sep 1935 – Dec 1938:

Site Construction

Construction at the observatory site included building of support structures and paving of a suitable road up to the site.

1:10 scale model completed

1:10 Scale Model Completed

A 1:10 scale model of the 200-inch telescope was built to ensure success with the mechanical problems to be surmounted in building the actual instrument. The model, made into a working telescope, was installed on the roof of the Astrophysics Laboratory.

radio antenna installed


Radio Astronomy

A prototype 32-foot diameter antenna was erected at Palomar to support Caltech's new radio astronomy program. The antenna was moved to the Owens Valley Radio Observatory in 1958.

Palomar and Mt. Wilson become the Hale Observatories


The Hale Observatories

The Mount WIlson and Palomar Observato­ries, administered jointly since 1928 until 1980, changed their joint name to the Hale Observatories.

WWII interruption

telescope and dome construction

1935 –1936:

Telescope and Dome Construction

In 1935, $25,000 of the Rockefeller grant were set aside to fund the building of the 18-inch Schmidt telescope. The telescope and its dome were finished within a year.

first light

Sep 5, 1936:

First Light

The 18-inch Schmidt became Palomar's first research telescope when Fritz Zwicky put it in operation the night of September 5, 1936.

supernova search and galaxy clustering observations

Sep 1936 – Jan 1942:

Supernovae and Galaxy Clusters

Fritz Zwicky began immediately using the 18-inch Schmidt for his supernova and galaxy clustering studies. He and Josef J. Johnson discovered a total of 19 supernovae until World War II interrupted the search program in January 1942.

galaxy clustering observations

1950 – 1957:

Galaxy Clusters

Fritz Zwicky continued his research on the clustering of galaxies during the 1950s.
Between 1961 and 1968, he published A New Catalogue of Bright Galaxies and Clusters of Galaxies in 6 volumes containing about 10,000 rich clusters of galaxies and 35,000 galaxies.

nova search program

Jul – Oct 1950:

Nova Search Program

Fritz Zwicky and Emil Herzog used the 18-inch Schmidt to conduct a systematic search for novae. The three-month search yielded three novae in the same field in Scorpius.

Palomar Supernova Search

1954 – 1975:

Palomar Supernova Search

The supernova search program with the 18-inch Schmidt was resumed in 1954 by Paul Wild, later joined by H. S. Gates, Fritz Zwicky and others. The program continued in conjunction with the larger Schmidt starting in 1959 and ended in late 1975.

Palomar Planet-Crossing Asteroid Survey (PCAS)

Jan 1973 – Jun 1995:

Palomar Planet-Crossing Asteroid Survey (PCAS)

The Palomar Planet-Crossing Asteroid Survey (PCAS) was a 23-year-long photo­graphic program led by Eleanor Helin and Eugene Shoe­maker (prior to 1982) dedi­cated to the detection of near-Earth objects (NEOs). The search yielded 65 mapped NEOs.

Palomar Asteroid and Comet Survey (PACS)

Sep 1982 – Dec 1994:

Palomar Asteroid and Comet Survey (PACS)

The Palomar Asteroid and Comet Survey (PACS), led by Eugene and Carolyn Shoe­maker, searched for asteroids that could cross Earth's orbit and potentially collide with it. This survey yielded 42 of these objects.

comet Shoemaker-Levy 9 discovered

March 24, 1993:

Discovery of Comet Shoemaker-Levy 9

The famous comet Shoemaker-Levy 9 was discovered with the 18-inch in 1993. The fragmented comet collided with Jupiter a year later in a spec­tacular astro­nomical show that captured the world's attention.

telescope on display

September 22, 2013:

Telescope on Display

Thanks to the genero­sity of the Eleanor and Ronald Helin Trust, the 18-inch Schmidt was put on public display at the Observatory's Visitor Center.

telescope planning and design

1937 – 1938:

Telescope Planning and Design

Given the success of the 18-inch Schmidt telescope during the 1930s, resources for building a larger Schmidt were com­mitted in 1937 and plans were completed in 1938.

mirror casting

Oct 1938:

Mirror Casting

The 72-inch mirror blank for the 48-inch Schmidt was cast by Corning Glass Works in October and shipped to Pasadena in November 1938.

dome construction

1938 – 1939:

Dome Construction

The dome for the 48-inch Schmidt was built between 1938 ad 1939.

telescope construction

1939 – 1947:

Telescope Construction

The mount and tele­scope tube were fabri­cated at the Caltech instrument shop. Due to war-related delays, the parts were not completed until 1947.

optics figuring and testing

1939 – Sep 1948:

Optics Figuring and Testing

The mirror and the re­fractive corrector plate were figured under the direction of Don Hendrix of the Mount Wilson optical shop at Carnegie. The optics were tested in the telescope in September 1948.

first image

Sep 29, 1948:

First Image

An image of M31, the Andromeda Galaxy, was the first official photograph taken with the 48-inch Schmidt on September 29, 1948.

National Geographic Society–Palomar Observatory Sky Survey (POSS I)

Nov 1949 – Dec 1958:

National Geographic Society–Palomar Observatory Sky Survey (POSS I)

The National Geogra­phic Society–Palomar Observatory Sky Survey (POSS I) was the first compre­hensive photographic survey of the entire northern sky. It became the standard library reference for every major observa­tory worldwide. Most of the survey was com­pleted by June 1956 but was not finished until December 1958.

Palomar Supernova Search

1959 – Dec 1975:

Palomar Supernova Search

Milton Humason revived the search for supernovae with the 48-inch telescope. He was later joined by Fritz Zwicky, Charles Kowal and others who used both Schmidts for this program until 1975. The search with the 48-inch yielded the dis­covery of 178 super­novae, plus several dozen found in POSS I plates and plates taken for other purposes.

Palomar–Leiden Survey

Sep – Oct 1960:

Palomar–Leiden Survey

The Palomar–Leiden Survey of faint minor planets, led by Cornelis van Houten and collaborators, yielded over 2,000 newly-discovered asteroids (1,800 with orbital information) in eleven nights. This number was increased to 2,400 including 19 Trojans after further analysis of the plates.

Palomar Proper Motion Survey

Sep 1962 – 1971:

Palomar Proper Motion Survey

Willem Luyten con­ducted a photographic survey to determine the proper motions of stars. He measured tens of thousands of proper motions, discovered many of the stars closest to the Solar System, and provided important context for studies of galactic structure.

Palomar–Leiden Trojan Survey I



1971, 1973, 1977:

Palomar–Leiden Trojan Surveys

The three Palomar–Leiden Trojan surveys, led by Cornelis van Houten and Ingrid van Houten-Groeneveld during the fall months of 1971, 1973, and 1977, yielded thousands of newly-discovered asteroids including dozens of Trojans.

Quick V survey

1982 – 1984:

Quick V survey

The Quick V survey was used to form the northern half of Hubble Space Telescope's Guide Star Catalog. Included within it are the positions and bright­nesses for about 19 million stars and other objects.

new corrector and upgrades

1985 – 1987:


The 48-inch Schmidt was refurbished with a new achromatic corrector plate and autoguiding, among other upgrades. The upgrades were mostly finished by mid-1987 at the beginning of the Second Palomar Sky Survey.



The Samuel Oschin Telescope

The 48-inch Schmidt was named the Samuel Oschin Telescope in 1987 to recognize a generous donation to Palomar Observatory by the Oschin family.

Second Palomar Observatory Sky Survey (POSS II)

1985 – 2000:

Second Palomar Observatory Sky Survey (POSS II)

The Second Palomar Observatory Sky Survey (POSS II; digi­tized DPOSS) formed the basis for the STSci Digital Sky Survey, the second Hubble Space Telescope Guide Star Catalog, and the United States Naval Observatory astro­metric and photometric catalogs, all of which contain over 1 billion stars and over 50 million galaxies.

robotic upgrade

1999 – Apr 2001:

Robotic and CCD Upgrade

In preparation for its next survey, the Samuel Oschin telescope was modified for robotic operation and the original photo­graphic equipment was replaced with its first CCD camera.

Near-Earth Asteroid Tracking (NEAT)

Apr 2001 – Apr 2007:

Near-Earth Asteroid Tracking (NEAT)

Led by JPL's Steven Pravdo, Eleanor Helin and others, the Near-Earth Asteroid Tracking (NEAT) program surveyed the sky for Solar System fast-moving objects, also finding variable stars and transient events. At Palomar, NEAT discovered close to 300 near-Earth asteroids and 13 comets.

Quasar Equatorial Survey Team (QUEST)

Jul 2003 – Sep 2008:

Quasar Equatorial Survey Team (QUEST)

The Quasar Equatorial Survey Team (QUEST) was a collaboration be­tween Charles Baltay (Yale) and George Djorgovski (Caltech). It focused on searching for variable stars, quasars, gravita­tional lenses, and distant supernovae. It pioneered the auto­mated classification of transients by pro­cessing data in real-time.

Eris discovered

Jan 5, 2005:

Discovery of Eris

Mike Brown and his team discovered the transneptunian object (TNO) Eris, which is about one quarter more massive than Pluto. This and other TNOs discovered by the team resulted in the revision of the definition of a planet by the Astro­nomical Inter­national Union and the designa­tion of Pluto and other smaller bodies as dwarf planets.

Palomar Transient Factory (PTF)

2009 – 2012:

Palomar Transient Factory (PTF)

The Palomar Transient Factory (PTF), a collaboration between Caltech and several other institutions, was a fully-automated, wide-field survey designed to search for optical tran­sient and variable sources. Between early 2009 and late 2012, it discovered tens of thousands of new tran­sient sources including thousands of new supernovae, novae, and cataclysmic variable stars.

intermediate Palomar Transient Factory (iPTF)

2013 – present:

Intermediate Palomar Transient Factory (iPTF)

This project was built upon the legacy of the Palomar Transient Factory (PTF). With improved software for data reduction and source classification, since February 2013 the project achieved significant successes in the early discovery and rapid follow-up studies of tran­sient sources. In 2017, iPTF transi­tioned to the Zwicky Tran­sient Factory (ZTF).

mirror casting

Mar 1934 – Oct 1935:

Mirror Casting

The 200-inch mirror was cast by Corning Glass Works. A failed attempt took place on March 25, 1934. A second disk was cast on December 2, 1934. The disk remained in the oven at pouring temperature for just over a month and then was gradually cooled over a period of ten months.

mirror figuring, testing, and adjusting

May 1936 – Oct 1949:

Mirror Figuring, Testing, and Adjusting

Under the direction of John A. Anderson and Marcus H. Brown at Caltech, the mirror disk was ground and figured into the proper shape. Including the delays from World War II, the disk was in the optical shop for 11 ½ years. The mirror went through an additional two years of testing, polishing, and adjusting at Palomar.

transport to Caltech

Mar – Apr 1936:

Mirror Transport to Caltech

On March 26, 1936, the 200-inch mirror blank began its 16-day trip by rail from Corning to the Caltech optical shop in Pasadena. All across the country thousands of people lined the train tracks to watch it pass. The mirror arrived safely to Pasadena on April 10.

dome construction

1936 – 1939:

Dome Construction

The first load of mate­rial for erecting the dome for the 200-inch telescope arrived at Palomar in September 1936. Building of the dome took place between then and 1939 under the watchful eye of superintendent of construction Byron Hill.

telescope design

1929 – 1936:

Telescope Design

The overall design of the 200-inch Hale Telescope is attributed to Russell Porter and Francis Pease, while engineering of its various aspects to Mark Serrurier, Sinclair Smith, Bruce Rule, Rein Kroon, and others. General specifi­cations were agreed upon in 1929. Design of the control system would not be com­pleted until mid-1938.

telescope construction and assembly

1936 – 1939:

Telescope Construction and Assembly

The fabrication of the 200-inch telescope began in 1936 primarily at the Westinghouse South Philadelphia and East Pittsburgh plants. After completion of the main parts in August 1938, the first components arrived at Palomar in October that year. Assembly was finished in the spring of 1939.

parts arrive at Palomar


Telescope Parts Arrive at Palomar

The 200-inch telescope parts were shipped by boat from the East Coast through the Panama Canal to San Diego and trucked to Palomar Mountain for assembly inside the dome. The first components arrived at Palomar in October 1938.

transport to Palomar

Nov 18 – 19, 1947:

Mirror Transport to Palomar

The 200-inch mirror left the Caltech optical shop on November 18, 1947 and arrived at Palomar a day later. It was transported on the back of a flatbed truck with two additional trucks behind it pushing it up highway S-6 and to the Observatory site.


Jun 3, 1948:

Dedication of Palomar Observatory and Hale Telescope

While not quite com­pleted, the 200-inch was dedicated as the Hale Telescope on June 3, 1948 in a cere­mony with speakers from Caltech and the Carnegie Institution, plus nearly 1000 invited guests seated under the telescope on the observing floor.

first image

Jan 26, 1949:

First Official Image

The first official exposure by the Hale Telescope, that of the NGC 2261 variable nebula, was taken by Edwin Hubble from the prime focus observing cage on the night of January 26, 1949.

cosmic distance scale corrected


Cosmic Distance Scale Corrected

Walter Baade hoped to resolve certain kind of variable stars in the Andromeda Galaxy expected to be seen by the Hale Telescope. His unsuccessful attempt led to a correction in previous distance estimates to the neighboring galaxy: the galaxy was twice as far as previously thought. To an astro­nomer, the size of the visible Universe had just doubled.

Hubble Constant refined


Hubble Constant Refined

In a paper published in 1958 based on data obtained with the Hale Telescope, Allan Sandage again increased the size of the visible Universe and brought the value of the Hubble Constant to 75km/s/Mpc, close to its modern value almost 50 years later.

3C 273 and 3C 48 identified


Quasars 3C 273 and 3C 48 Identified

The radio-loud objects 3C 273 and 3C 48 were spectroscopically studied by Maarten Schmidt and collaborators in 1963. The features in the unusual spectra were greatly redshifted due to the expansion of the Universe. These quasi-stellar radio sources, or quasars, were among the most distant astronomical bodies ever observed: several billion light-years away.

infrared observations of the galactic center

Sep 1966:

Infrared Observations of the Galactic Center

Infrared astronomy pioneers Gerry Neugebauer and Eric Becklin observed the galactic center, obscured in visible light by dust, using a single-cell infrared detector on the Hale Telescope.

first electronic instruments


First Electronic Instruments

The earliest electronic instrument on the Hale Telescope was a pulse-counting photo­meter mounted on the prime focus. It was developed by William Baum and with it he showed that the tele­scope could photo­graph astro­no­mical bodies which are at least 6,300,000 times dimmer than those visi­ble to the naked eye.

first computer system


First Computer System

The first computer system for telescope control and data acqui­sition was designed and installed in 1971 by Edwin Dennison.

early CCD instruments

1976 – 1979:

Early CCD Instruments

The first use of CCDs at Palomar Observa­tory occurred in May 1976. It was a 100×160 pixel CCD camera designed by Beverley Oke and collaborators for spectrographic work. The first instru­ment designed speci­fically to use CCDs was the Prime-Focus Universal Extragalactic Instrument (PFUEI) built in 1979 by James Gunn and James Westphal. It used first a 500×500 and later a 800×800 pixel CCD.

Four-Shooter installed


Four-Shooter Installed

Four-Shooter, the pro­to­type for the Hubble Space Telescope WFPC camera, was installed on the Hale Telescope in 1983. It was built for Palomar at the Jet Propulsion Laboratory under the leadership of James Gunn and James Westphal. Four-Shooter was used at least until the late 1980s.

first adaptive optics system operational

Dec 1999:

First Adaptive Optics System Operational

The first adaptive optics system for the Hale Telescope, PALAO, started regular operations in Decem­ber 1999. It was deve­loped in the mid to late 1990s by a Caltech and JPL team led by Richard Dekany and Mitchell Troy.

PALM-3000 operational

Jun 2011:

PALM-3000 Operational

PALM-3000, the Hale Telecope's new adaptive optics system, started science opera­tions in June 2011. It was developed by Richard Dekany and collaborators as an upgrade to the PALAO system.

telescope and dome design

1962 – 1966:

Telescope and Dome Design

Planning for the 60-inch telescope began in 1962. Funded by NASA, the design studies and engi­neering plans were con­ducted by Bruce Rule, while Ira Bowen designed the Ritchey–Chrétien optical system.

mirror casting


Mirror Casting

Coming Glass Works of Bradford, Pennsyl­vania, cast the 61-inch fused silica (quartz) mirror blank.

optics grinding and figuring

1966 – 1969:

Optics Grinding and Figuring

The grinding and polishing of the optics were done by Floyd Day and the staff of the Mount Wilson optical shop in Pasadena.

mount and dome construction, control system development

1966 – 1970:

Mount and Dome Construction, Control System Development

The telescope structure was built in the Caltech Central Engineering Services shop with funds provided by the National Science Foundation. The dome, designed by Richard W. Rose and built by Western Gear Corpo­ration, was financed by the Oscar G. Mayer family. The automated telescope control and data acquisition system was developed by Edwin Dennison and his team.


Oct 23, 1970:


The 60-inch telescope and the Oscar G. Mayer Memorial Building were dedicated on October 23, 1970.

Gliese 229B confirmed

Oct 1994:

Gliese 229B Confirmed

The first brown dwarf ever to be confirmed, Gliese 229B, was discovered in October 1994 using the 60-inch telescope with the Adaptive Optics Coronagraph built at Johns Hopkins.

robotic upgrade


Robotic Upgrade

A team led by S. Bradley Cenko converted the 60-inch telescope from a classic night-assistant-operated telescope to a fully robotic facility. The automated system became operational in September 2004 and was designed for fast and sustained observations of transient events.

Robo-AO operational

2012 – 2015

Robo-AO Operational

Robo-AO, an auto­nomous and portable AO system designed by Christoph Baranec and collaborators for medium-sized telescopes, operates robotically on the 60-inch telescope.

Palomar history graphical timeline. Time starts in 1920 and flows to the right; use the scroll bar to reach the 2010s. Each column corresponds to a decade, vertical lines indicate years. Rows indicate category: general or individual telescopes. Darker background shows when the telescope was operational. Each event is shown as a bar whose width indicates time span. Hovering with mouse over an event will bring up a short explanation. Hint: use the keyboard shortcuts (no shift) control/command + to zoom in, control/command − to zoom out, and control/command 0 to reset. Go to chronology.