Skylab 4 Imaged Comet Kohoutek During Second EVA on Christmas Day 1973

Summary: Skylab 4 imaged Comet Kohoutek during second EVA on Christmas Day, Dec. 25, 1973, three days before perihelion, the closest comet-to-sun distance.

Comet Kohoutek, at three days’ distance from perihelion; false-color reproduction of black-and-white photograph taken during Christmas Day spacewalk, Dec. 25, 1973, by Skylab 4 mission pilot William Pogue, with far-ultraviolet electrographic camera; yellow (center) is brightest area, with outward color successions indicating decreasing brightness; C.A. Lundquist, Skylab’s Astronomy and Space Sciences (1979), Figure 4-1: "Work of the US Gov. Public Use Permitted," via NASA History

Skylab 4 imaged Comet Kohoutek during the second EVA, on Christmas Day, Dec. 25, 1973, three days before the recently discovered comet reached perihelion (Ancient Greek: περί, perí, “near” + ἥλιος, hḗlios, “sun”), its closest distance to the sun.

Czech astronomer Luboš Kohoutek (born Jan. 29, 1935) discovered his namesake comet via plates obtained Wednesday, March 7, 1973, at northern Germany’s Hamburg Observatory (Hamburger Sternwarte). The long-period comet was calculated to makes its perihelion (Ancient Greek: περί, perí, “near” + ἥλιος, hḗlios, “sun”) passage between December 1973 and January 1974 and to reach perihelion on Friday, Dec. 28, 1973.

Skylab 4 launched Friday, Nov. 16, 1973, from east central Florida’s John F. Kennedy Space Center as the National Aeronautics and Space Administration’s (NASA) third and last manned mission to Skylab, the first United States space station. Skylab had been launched into low Earth orbit six months earlier, on May 14, 1973, from Kennedy Space Center.

The three-astronaut crew of Skylab 4 made their first, and only, spaceflights via the mission. The mission’s commander was Gerald Paul Carr (born Aug. 22, 1932). Edward George Gibson (born Nov. 8, 1936) and William Reid Pogue (Jan. 23, 1930-March 3, 2014) served as the mission’s scientist pilot and pilot, respectively.

Carr and Pogue’s EVA (extravehicular activity) on Tuesday, Dec. 25, 1973, marked NASA’s first Christmas Day spacewalk and numbered as the mission’s second spacewalk. Gibson and Pogue had conducted Skylab 4 mission’s first EVA Thursday, Nov. 22, 1973, as NASA’s first Thanksgiving Day spacewalk.

EVA 2 began at 16:00 Coordinated Universal Time (11 a.m. Eastern Standard Time) and ended at 23:01 UTC (6:01 p.m. EST). Repairs and an unplanned issue with the station’s proper attitude prolonged the spacewalk from its originally scheduled length of 3 hours 50 minutes to its actual duration of 7 hours 01 minute. The record-breaking spacewalk’s length remained unsurpassed until the Aug. 31, 1985, EVA 1 of 7 hours 20 minutes conducted by James Dougal Adrianus “Ox” van Hoften (born June 11, 1944) and William Frederick Fisher (born April 1, 1946) during Space Shuttle Discovery’s sixth flight.

While Carr attended to the stuck filter wheel on the Apollo Telescope Mount’s (ATM) S056 X-ray Telescope, Pogue photographed Comet Kohoutek for the mission’s S201 experiment. Principal investigator Thornton Page designed the S201 experiment for studying Comet Kohoutek’s coma, or gaseous halo formed around the nucleus, in the far ultraviolet spectrum of electromagnetic radiation. Page had arranged for use and modification of one of the backup far-ultraviolet electrographic cameras designed by his U.S. Naval Research Laboratory (NRL) colleague, George Robert Carruthers (born Oct. 1, 1939), for the Apollo 16 mission (Sunday, April 16, to Thursday, April 27, 1972).

In an interview July 17, 2000, with NASA Johnson Space Center (JSC) historian Kevin M. Rusnak, Pogue recalled his outdoor photographs of Comet Kohoutek at three days’ distance from perihelion. “As a matter of fact, I took this instrument outside to take pictures and images of the comet,” Pogue related. “It was kind of tricky because I had to use one of the solar panels off of the ATM to shield the sun, because it was so close to the sun, it’s approaching the sun. So I finally got this thing into position and kind of eyeballed it so that the solar panel would be shading the sun” (pages 12-43 to 12-44).

The takeaways for Skylab 4’s images of Comet Kohoutek during the mission’s second EVA on Christmas Day 1973 are that the images capture the recently discovered comet at three days’ distance from perihelion and that over 11 years 8 months passed before Skylab 4’s record EVA length of 7 hours 1 minute was finally surpassed during Space Shuttle Discovery’s sixth flight.

(left) Figure 4-13: far-ultraviolet electrographic camera capture of Comet Kohoutek (white arrow; upper right) and stars, filtered for wavelengths from 125 to 160 nanometers (nm); Tuesday, Dec. 25, 1973; (right) Figure 4-14: false-color enhancement of Comet Kohoutek and stars from Figure 4-13 to reveal ranges of optical density (sky’s “brightness”) via corresponding color zones: C.A. Lundquist, Skylab’s Astronomy and Space Sciences (1979), Figures 4-13 to 4-14, pages 51-52: "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:

Comet Kohoutek, at three days’ distance from perihelion; false-color reproduction of black-and-white photograph taken during Christmas Day spacewalk, Dec. 25, 1973, by Skylab 4 mission pilot William Pogue, with far-ultraviolet electrographic camera; yellow (center) is brightest area, with outward color successions indicating decreasing brightness; C.A. Lundquist, Skylab’s Astronomy and Space Sciences (1979), Figure 4-1: "Work of the US Gov. Public Use Permitted," via NASA History @ https://history.nasa.gov/SP-404/ch4.htm#4.18

(left) Figure 4-13: far-ultraviolet electrographic camera capture of Comet Kohoutek (white arrow; upper right) and stars, filtered for wavelengths from 125 to 160 nanometers (nm); Tuesday, Dec. 25, 1973; (right) Figure 4-14: false-color enhancement of Comet Kohoutek and stars from Figure 4-13 to reveal ranges of optical density (sky’s “brightness”) via corresponding color zones: C.A. Lundquist, Skylab’s Astronomy and Space Sciences (1979), Figures 4-13 to 4-14, pages 51-52: "Work of the US Gov. Public Use Permitted," via NASA History @ https://history.nasa.gov/SP-404/ch4.htm#4.18

For further information:

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Available @ https://history.nasa.gov/SP-400/ch9.htm

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Available @ https://history.nasa.gov/SP-4208/ch17.htm

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