Skylab 4 Imaged Comet Kohoutek’s Hydrogen Halo November 1973 to February 1974

Summary: Skylab 4 imaged Comet Kohoutek’s hydrogen halo November 1973 to February 1974 with Apollo 16 mission’s backup far-ultraviolet electrographic camera.

geometry of pre-perihelion observation of Comet Kohoutek; C.A. Lundquist, Skylab’s Astronomy and Space Sciences (1979), Figure 4-7: "Work of the US Gov. Public Use Permitted," via NASA History

Skylab 4 imaged Comet Kohoutek’s hydrogen halo November 1973 to February 1974 with the Apollo 16 mission’s backup far-ultraviolet electrographic Schmidt camera as the recently discovered comet made its closest passage to the sun.

Czech astronomer Luboš Kohoutek (born Jan. 29, 1935) is credited with discovering the long-period comet via plates taken Wednesday, March 7, 1973, at northern Germany’s Hamburg Observatory (Hamburger Sternwarte). Calculations placed Friday, Dec. 28, 1973, as the date for the comet’s reach of perihelion (Ancient Greek: περί, perí, “near” + ἥλιος, hḗlios, “sun”).

The National Aeronautics and Space Administration (NASA) revised time parameters for Skylab 4, the third manned mission to the first United States space station, to overlap with Comet Kohoutek’s December 1973 to January 1974 perihelion passage. Skylab 4 launched Friday, Nov. 16, 1973, at 14:01:23 Coordinated Universal Time (9:01 a.m. Eastern Standard Time) from east central Florida’s John F. Kennedy Space Center. The Apollo module’s successful Pacific Ocean splashdown Friday, Feb. 8, 1974, at 15:16:53 UTC (10:16 a.m. EST) signaled the completion of the Skylab 4 mission.

Gerald Paul Carr (born Aug. 22, 1932) commanded the Skylab 4 mission. Edward George Gibson (born Nov. 8, 1936) and William Reid Pogue (Jan. 23, 1930-March 3, 2014) participated as the mission’s scientist pilot and pilot, respectively. All three astronauts logged their first, and only, spaceflight via the Skylab 4 mission.

The mission’s Experiment S201 called for imaging the immense hydrogen halo layering outside the comet’s fuzzy coma. Thornton Leigh Page (Aug. 13, 1913-Jan. 2, 1996) of the United States Naval Research Laboratory (NRL) and NASA’s Lyndon B. Johnson Space Center, served as the experiment’s principal investigator. S201 necessitated a far-ultraviolet electrographic Schmidt camera, an instrument not already among Skylab’s onboard instrumentation array.

Page had collaborated with George Robert Carruthers (born Oct. 1, 1939) in the S201 far-ultraviolet camera study that was conducted as part of the Apollo Lunar Surface Experiments Package (ALSEP) during the Apollo 16 mission’s stay on the lunar surface in April 1972. Carruthers is credited with inventing and building the experiment’s gold-plated, electrographic Schmidt camera-based instrument, which was left at the Apollo 16 mission’s landing site in the Descartes Highlands in the central lunar highlands.

The Naval Research Laboratory minorly modified a backup model of Carruthers’ lunar surface camera to allow for observations at Skylab space station via the antisolar Scientific Air Lock (SAL), the Articulated Mirror System (AMS) or Extravehicular Activity (EVA). The modified camera journeyed with Skylab 4 mission’s crew to the space station in Apollo Command and Service Module (CSM) 118.

Between Monday, Nov. 26, 1973, and Saturday, Feb. 2, 1974, the far-ultraviolet camera captured 126 frames of Comet Kohoutek. In his preliminary report on Skylab’s far-ultraviolet photographs of Comet Kohoutek, published in 1975, Thornton Page announced that 30 of the frames had been “. . . measured for analysis of the comet’s hydrogen halo on nine separate dates from 31.7 days pre-perihelion to 13.0 days post-perihelion” (page 37).

The hydrogen halo’s brightness and diameter were plotted relative to time and comet-to-sun distance. An expected increase in the halo generally occurred with decreasing distance. Page noted, however, “an unexpected pre-perihelion maximum” on Wednesday, Dec. 12, at a comet-to-sun distance of 0.6 astronomical units (au) (89,758,722 kilometers; 55,773,484 miles). Page’s analysis found a much larger ratio of peak nuclear brightness to diameter near perihelion. “Such an increase in ‘concentration’ of the hydrogen halo might be expected from the increase in hydrogen production from the comet nucleus near perihelion,” he explained (page 55, 64).

The takeaways for Skylab 4’s images of Comet Kohoutek’s hydrogen halo are that the halo showed an unexpected increase in brightness and diameter on Wednesday, Dec. 12, and that images were obtained by one of the backup far-ultraviolet electrographic cameras invented by principal investigator Thornton Page’s Naval Research Laboratory colleague George Roberts Carruthers for the Apollo 16 mission.

six frames of Skylab 4 Far Ultraviolet Electronographic (S201 experiment) show Comet Kohoutek’s halo; NASA ID s74-20010: 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

Acknowledgment

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

Image credits:

geometry of pre-perihelion observation of Comet Kohoutek; C.A. Lundquist, Skylab’s Astronomy and Space Sciences (1979), Figure 4-7: "Work of the US Gov. Public Use Permitted," via NASA History @ https://history.nasa.gov/SP-404/ch4.htm

six frames of Skylab 4 Far Ultraviolet Electronographic (S201 experiment) show Comet Kohoutek’s halo; NASA ID s74-20010: 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/s74-20010

For further information:

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