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CGROTL - CGRO Timeline



The Compton Gamma-Ray Observatory (CGRO) was the second of NASA's Great Observatories. It was launched on April 5, 1991, from Space Shuttle Atlantis. It operated successfully for 9 years, and then was safely de-orbited and re-entered the Earth's atmosphere on June 4, 2000.

Compton had four instruments that covered an unprecedented six decades of the electromagnetic spectrum, from 30 keV to 30 GeV. In order of increasing spectral energy coverage, these instruments were the Burst And Transient Source Experiment (BATSE), the Oriented Scintillation Spectrometer Experiment (OSSE), the Imaging Compton Telescope (CompTel), and the Energetic Gamma Ray Experiment Telescope (EGRET). BATSE viewed the full sky, as a transient monitor and is thus not included in this database table of pointed telescope observations. Also, EGRET and CompTel had wide fields of view, about 30 degrees, and, as such, viewed multiple targets per X-axis pointing. OSSE could be slewed (about one axis) independently from the spacecraft, so it typically viewed 2 targets per spacecraft Z-axis orientation, or "viewing period." Viewing periods were typically two weeks long.

This database table contains the CGRO observations for Cycles 1 through 9. The Cycle 1 observations for EGRET and COMPTEL were part of the All-Sky Survey with no defined targets.


The Compton Observatory Science Support Center observation timelines are available at


This database table was last updated in November 2001. The information contained therein was provided by the Compton Observatory Science Support Center (COSSC). Galactic coordinates were added to the table by the HEASARC in August 2005. Duplicate entries in the table were removed in June 2019.


The proposal phase/cycle number.

The viewing period of the observation.

The start date of the viewing period.

The end date of the viewing period.

The unique proposal number from which the observation was derived.

The last name of the Principal Investigator of the observation or the instrument team.

The instrument(s) used for the observation, where O = OSSE, C = CompTel, and E = EGRET.

The primary target's Right Ascension.

The primary target's Declination.

The primary target's Galactic longitude.

The primary target's Galactic latitude.

The designation of the primary target.

Estimated exposure of the target (in seconds). Off-axis targets are weighted by the angular response function of EGRET and COMPTEL respectively.

The angle between target and z-axis of the spacecraft. This number is important for EGRET and COMPTEL, which point in the z-axis direction.

Contact Person

Questions regarding the CGROTL database table can be addressed to the HEASARC Help Desk.
Page Author: Browse Software Development Team
Last Modified: Thursday, 10-Feb-2022 20:44:15 EST