OAO 2

About This Satellite

Orbiting Astronomical Observatory 2, nicknamed Stargazer, launched on December 7, 1968. It opened a sustained view of stellar ultraviolet radiation that Earth's atmosphere largely prevents ground-based telescopes from observing. The mission also developed the practical ability to point at an astronomical target and hold that direction long enough for useful measurements.

Imaging and measuring brightness were separate approaches

OAO 2 carried the Smithsonian Celescope experiment and the Wisconsin Experiment Package. The latter combined stellar and extended-source photometers with scanning spectrometers. Brightness measurements and spectra can answer questions about a source without producing a detailed photograph. Not every telescope aboard the observatory was performing the same kind of observation.

An instrument shutdown was not the spacecraft shutdown

NASA records Celescope being turned off in April 1970 after detector sensitivity declined, while the spacecraft continued until February 1973. A search for late-mission observations must therefore identify the instrument. Using only the overall mission dates could incorrectly imply that Celescope was still collecting data throughout that interval.

Mission reference: NASA: OAO 2 ultraviolet instruments, pointing and mission history. Editorial review: 2026-09-14.

A source catalog is not the same thing as a stack of frames

The Smithsonian's Celescope report describes a catalog containing 5,068 stars and documents the data-tape format and software used to read it. This is a processed observational product, not one entry for every image exposure. Repeated frames, measurements, and identified sources represent different quantities; comparing them without checking their definitions can make a survey appear larger or smaller than it was.

Reference: Smithsonian/NASA NTRS: Celescope catalog content and data format.

A disappearing star could reveal ozone above Earth

A published investigation used OAO-2 Wisconsin photometers to measure ultraviolet starlight as Earth's atmosphere moved across the line of sight. Absorption near 250 nanometres allowed the researchers to derive nighttime ozone profiles over roughly 60 to 100 km altitude from about twelve low-latitude occultations. This was a limited set of atmospheric soundings, not a continuous global ozone map or a direct view of the ground below the satellite.

Reference: NASA NTRS: OAO-2 stellar occultations and mesospheric ozone profiles.

Reading this orbital snapshot

Based on TLE epoch: 2026-09-05. Estimated altitude ranges from 730 km at perigee to 738 km at apogee, a difference of 8 km. The orbital period is about 99.5 minutes. Eccentricity 0.00056 indicates a nearly circular path. In a two-body approximation, perigee speed is 1.00 times apogee speed. These are mean-element estimates, not instantaneous measurements. Distance per orbit uses an ellipse approximation.

Saved build snapshot. If a valid TLE is retrieved, this explanation and the orbit panel update together. Otherwise this dated snapshot is retained.

Ground track is not sensor coverage

An inclination of 34.99 degrees implies approximate geocentric ground-track limits of 35.0 degrees north and south. This is a prograde orbit, moving in the same general direction as Earth rotation. The plotted line marks the point beneath the object. It does not represent camera coverage, radio reception, or a guaranteed visible pass.

Accuracy and missing information

The introductory record describes the build snapshot. The orbital snapshot explanation and orbit panel share any successfully retrieved TLE; check the displayed epoch. Reentered objects retain historical data only. Mission history is not rewritten by TLE updates. TLE/SGP4 positions are predictions and can change after maneuvers or updated observations. The 14-day stale-data cutoff is a display safeguard, not an accuracy guarantee. Local passes are geometric predictions, not a visibility forecast. No verified operator or mission status means unknown, not active. Do not use this catalog for collision avoidance or operational flight decisions.

Catalog sources: CelesTrak SATCAT: NORAD 3597 · GCAT: S03597 (source update 2026 Sep 4 2345:57). Supplementary metadata: SatNOGS DB, retrieved 2026-09-05T12:57:25.375Z. Page assembled 2026-09-15. GCAT phase codes describe trajectory phases, not mission health.

Learn more: TLE data · Perigee and apogee · Ground tracks · JOT (Jewawud Live Orbital Map)

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