Skylab 4 Began Observing Comet Kohoutek in November 1973

Summary: The Skylab 4 mission began observing Comet Kohoutek in November 1973 as the recently discovered comet orbited through the inner solar system.

artist’s concept of observations of Comet Kohoutek by Skylab 4 astronauts through the scientific airlock in the space station’s Orbital Workshop; illustration created Nov. 27, 1973; NASA ID s73-37274: NASA, Generally not subject to copyright in the United States; may use this material for educational or informational purposes, including photo collections, textbooks, public exhibits, computer graphical simulations and Internet Web pages; general permission extends to personal Web pages, via NASA Image and Video Library

The Skylab 4 mission began observing Comet Kohoutek in November 1973 as the recently discovered long-period comet continued its passage through the inner solar system.

Czech astronomer Luboš Kohoutek (born Jan. 29, 1935) discovered Comet Kohoutek at the Hamburg Observatory (Hamburger Sternwarte) in northern Germany. Officially designated as C/1973 E1, Comet Kohoutek was discovered Wednesday, March 7, 1973, in the direction of Hydra the Sea Serpent Constellation, according to NASA Goddard Space Flight Center astronomer Robert D. Chapman in Comet Kohoutek: A Teacher's Guide (1973). Calculations identified Friday, Dec. 28 as the date of the newly discovered comet’s perihelion (Ancient Greek: περί, perí, “near” + ἥλιος, hḗlios, “sun”), closest passage to the sun.

In response to Kohoutek’s discovery, the National Aeronautics and Space Administration (NASA) initiated Operation Kohoutek, headed by Stephen Paul Maran, an astrophysicist at NASA’s Goddard Space Flight Center since 1969. The multi-resource program aimed to coordinate widespread ground, air and space observations of the comet.

Skylab 4 launched Friday, Nov. 16, 1973, at 14:01:23 Coordinated Universal Time (9:01 a.m. Eastern Standard Time) from Cape Canaveral, east central Florida, as NASA’s third manned mission to Skylab, the first United States space station. The three-astronaut crew comprised Gerald Paul Carr (born Aug. 22, 1932) as commander; Edward George Gibson (born Nov. 8, 1936) scientist pilot; and William Reid Pogue (Jan. 23, 1930-March 3, 2014) as the mission’s pilot. The mission’s Apollo Command and Service Module (CSM) 118 docked at Skylab at 21:55:00 UTC (4:55 p.m. EST). The mission’s Apollo Command and Service Module (CSM) 118 docked at Skylab at 21:55:00 UTC (4:55 p.m. EST).

NASA finessed the Skylab 4 mission’s time parameters to maximize perihelion-centered observations. As Charles Lundquist, director of the Space Sciences Laboratory at NASA’s George C. Marshall Space Flight Center in Huntsville, Alabama, explained in Skylab’s Astronomy and Space Sciences (1979): “It is during this period that the most interesting and dramatic changes happen to comets, and it is also during this period that observations from the Earth’s surface are hardest to make or even impossible because light from the nearby Sun is scattered by the Earth’s atmosphere into instruments aimed at the comet” (page 43).

“Systematic comet observations” were initiated on Friday, Nov. 23, according to authors William David Compton and Charles Dunlap Benson in Living and Working in Space: A History of Skylab, published by NASA in 1983. The camera associated with Charles Lundquist’s photometric studies (Skylab Experiment S233) was designated as the first instrument to gather data on the comet. Photometry concerns measurement of visible light in terms of human perception of light’s brightness.

The Skylab space station’s 35-mm Nikon camera, which had a 55-mm focal length and a focal range from two feet to infinity, was used for the experiment. Four cassettes of 60-exposure Kodak Plus-X Aerial 3401 film were supplied for the experiment.

Calibrated photometric data was to be obtained from a twice daily observational sequence of defocused and in-focus photographs. Defocused photographs of the coma and starfields were to be obtained at a specified focus setting of 15 feet. Long duration in-focus photographs were to record as much of the comet’s tail structure as possible. In his final report of the experiment, published in 1981, Charles Lundquist explained that the operation plan of twice daily photographs “. . . could serve as a reference record of the gross changes in the comet appearance and magnitude” (page 2).

The photometric study’s photographs were taken inside the space station. Photography sessions took place at window number one (CM-1) in the Apollo Command and Service Module (CSM) and windows three (STS-243; S-3) and four (STS-242; S-4) in the Structural Transition Section (STS) linking the station’s Airlock Module (AM) and Multiple Docking Adaptor (MDA). The mission’s astronauts were responsible for manually pointing the Nikon camera at the comet. The George C. Marshall Space Center’s MSFC Skylab Kohoutek Project Report, published in 1974, noted that “. . . the astronauts taped the camera to a rotatable mirror structure over the CM-1 window and improvised cardboard to tape the camera in place at the STS-242 and STS-243 windows” (page 43).

Pilot Pogue is credited with the last photographs for Experiment S233. Frame 52, at the infinity setting, and frame 53, at the 15-foot focal length, were obtained Feb. 5, 1974, at 01:03 UTC (9:03 p.m. Eastern Daylight Time, Monday, Feb. 4, 1974). Pogue was stationed at window four (STS-4; S-4) in the Structural Transition Section.

The takeaways for Skylab 4 beginning observations of Comet Kohoutek in November 1973 are that the mission’s time parameters coincided with the recently discovered comet’s perihelion passage between December 1973 and February 1974 and that the first Kohoutek-based experiment operated from Friday, Nov. 23, 1973, to Monday, Feb. 5, 1974.

Comet Kohoutek’s perihelion passage December 1973 to February 1974; C.A. Lundquist, Skylab’s Astronomy and Space Sciences (1979), Figure 4-6: "Work of the US Gov. Public Use Permitted," via NASA History

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

artist’s concept of observations of Comet Kohoutek by Skylab 4 astronauts through the scientific airlock in the space station’s Orbital Workshop; illustration created Nov. 27, 1973; NASA ID s73-37274: NASA, Generally not subject to copyright in the United States; may use this material for educational or informational purposes, including photo collections, textbooks, public exhibits, computer graphical simulations and Internet Web pages; general permission extends to personal Web pages, via NASA Image and Video Library @ https://images.nasa.gov/details/s73-37274

Comet Kohoutek’s perihelion passage December 1973 to February 1974; C.A. Lundquist, Skylab’s Astronomy and Space Sciences (1979), Figure 4-6: "Work of the US Gov. Public Use Permitted," via NASA History @ https://history.nasa.gov/SP-404/p47.htm

For further information:

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