Palomar

Mapping the Cosmos: The Palomar Astronomical Database & Sky Surveys

When astronomers speak of the Palomar database, they are usually referring to the monumental photographic and digital sky surveys conducted at the Palomar Observatory in Southern California (owned and operated by the California Institute of Technology - Caltech). These surveys mapped the northern skies for decades, serving as the foundational roadmap for modern observational astronomy.

History & Who Made It

The legacy of Palomar’s sky surveys spans two major generations, driven by pioneering astronomers and institutions:

POSS-I (Palomar Observatory Sky Survey I): Conducted between 1949 and 1958, this was jointly funded by the National Geographic Society and the Palomar Observatory (National Geographic Society – Palomar Observatory Sky Survey, or NGS-POSS). The primary minds behind its inception and execution included astronomical giants like Edwin Hubble, Walter Baade, Milton Humason, Ira Bowen, and Rudolph Minkowski. It utilized the landmark 48-inch (1.2-meter) Samuel Oschin Schmidt Telescope.

POSS-II and DPOSS (Digital Palomar Observatory Sky Survey): Running from the late 1980s through the 1990s, POSS-II updated the survey using finer-grain photographic emulsions across three broad wavelength bands. This analog archive was later scanned into high-resolution digital databases at Caltech, creating the Palomar-Norris Sky Catalog (PNSC) and making it machine-readable for modern computational astronomy.

The Purpose

Before the era of wide-field electronic CCD detectors, astronomers lacked a comprehensive, uniform map of the northern sky. The core objectives of the Palomar surveys were:

To Create a Universal Reference Map: To photographically capture every accessible portion of the northern night sky down to faint limiting magnitudes, providing a permanent historical snapshot of the cosmos.

To Guide Big Telescopes: To serve as a master finding chart for the 200-inch (5.1-meter) Hale Telescope and other world-class instruments, pointing them toward interesting variable stars, distant nebulae, radio sources, and clusters.

To Enable Statistical and Cosmological Studies: To quantify the distribution of galaxies, map the Milky Way's stellar density, and discover rare cosmic phenomena (such as high-redshift quasars and near-Earth asteroids).

What Objects and How Many?

The digital incarnations of the Palomar database (such as DPOSS and the PNSC) contain an astronomical volume of celestial bodies:
Stars: Over 2 billion stars of our Milky Way galaxy, mapped across various color bands (blue, red, and near-infrared).
Galaxies: More than 50 million individual galaxies, reaching deep into the universe (median redshifts around z ~ 0.2, probing out to z ~ 0.5).
Exotic & Transient Objects: Hundreds of thousands of quasars, planetary nebulae, high-proper-motion stars, and a specialized sub-catalog of 15 faint Palomar Globular Clusters (discovered lingering in the outer halo of our galaxy).

Highlights & Major Discoveries

The plates and data derived from Palomar have fueled an incredible array of breakthroughs:

Quasars (Quasi-Stellar Objects): Observations utilizing Palomar data allowed astronomer Maarten Schmidt to decode the extreme redshifts of stellar-like radio sources, discovering that they were actually massive, hyper-luminous active galactic nuclei at the edge of the observable universe.

Asteroid Discoveries: Shoemaker and other researchers used Palomar plates to uncover classes of near-Earth asteroids, including the first-discovered Aten and Apollo asteroids.

Supernovae & Comets: Dedicated observers (such as legendary Palomar astronomer Jean Mueller) discovered over 100 supernovae and multiple comets by systematically comparing historical Palomar plates with fresh exposures.

The Observer's Challenge: "Is It Really There?" (And How to Observe It)

For amateur astronomers and advanced backyard observers, the ultimate test involving this database is tracking down the Palomar Globular Clusters (often labeled Palomar 1 through Palomar 15).

Unlike bright showpiece clusters like M13, the Palomar globulars are faint, highly dispersed ghosts hiding deep in the galactic halo or behind thick dust lanes. Most were discovered only because they left faint smudges on the deep photographic plates of the POSS.

The Observer's Dilemma

When hunting a faint target like Palomar 4 or Palomar 13, you look through the eyepiece and see... absolutely nothing where the star chart says the cluster should be. This prompts the classic amateur astronomy existential crisis: "Is my telescope misaligned, is there dew on the lens, or am I actually looking at it?" Many of these clusters consist of loosely scattered, ancient stars that barely stand out against background noise.

How to Successfully Observe Them

Aperture & Dark Skies: While a few bright ones (like Palomar 12 or 13) can be glimpsed in medium-to-large amateur scopes (10 to 12 inches), most require large-aperture scopes (14 to 16+ inches), pristine dark skies (Bortle 3 or better), and exceptionally good seeing conditions.
Precise Star-Hopping & Blinking: Because they look like meager clumps of background field stars rather than majestic balls of light, you cannot rely on casual sweeping. You must use high-precision megastar charts or digital setting circles matched exact to Palomar database coordinates.
Averted Vision and Magnification: Use medium-to-high magnification to darken the sky background. Often, the cluster will only reveal itself as an extremely subtle, ghost-like gray "texture" or a triangular micro-pattern of 3 or 4 barely resolved pinpoint stars when using averted vision.
Verification: To confirm you've actually "bagged" a Palomar cluster, take a short digital exposure or a stacked electronic-assisted astronomy (EAA) snapshot with a sensitive camera, then cross-reference your field against the original Palomar digital sky survey image to verify if that faint, elusive smudge matches the catalog coordinates.