Sunday, August 20, 2017

On the Eve of the Great 2017 American Eclipse, Let's Revisit Skylab's Artificial Eclipses

NASA Marshall Space Flight Center (MSFC) image, the Sun's corona observed by Skylab. The corona in real color would actually be white; this computer-enhanced image uses false color to augment coronal features. "At Skylab's orbital altitude, where almost no air was left and where the sky was starkly black, the outer corona was at last clearly seen. In the thousands of coronal portraits made by Skylab, in which the corona was observed more extensively than in all the centuries of humanity's interest in the Sun, the corona was constantly altering its form, ever adjusting to the shifting magnetic fields from the Sun's surface that so obviously gave it its distinctive shape. Skylab's coronagraph observations coupled with x-ray pictures of the inner corona helped establish the origin of the corona's varied forms and the important connection between coronal holes and high-speed streams in the solar wind." (Author's note: All material in quotes is from NASA.)
DID YOU KNOW: Skylab boasted a white light coronagraph in its suite of eight Apollo Telescope Mount (ATM) experiments which allowed its astronauts to photograph incredible simulated eclipses? On the eve of tomorrow's solar eclipse, let's revisit this little-hyped, long-forgotten cool Skylab feature. 

According to the 1979 NASA publication A New Sun, "The white light coronagraph provided high resolution photographs of the corona in the visible region of the electromagnetic spectrum. To block out direct sunlight and reduce diffracted light to an acceptable level, three external occulting disks were employed. This allowed observations of the outer corona from 1.5 solar radii to a distance of 6 solar radii from the center of the Sun. The optical elements of the instrument also performed the function of variable vignetting, which enhanced faint outer corona detail and suppressed blooming in the bright inner corona. A precise brightness calibration of the data was obtained by imaging direct sunlight through an 18 step wedge filter. A TV camera in the instrument provided real-time pictures of the occulted Sun to the astronauts at the control console." 

Thanks to this instrument, solar experts in space (Dr. Ed Gibson, Skylab 4 crew member, is a solar physicist by trade) and on Earth enjoyed spectacular images of the Sun's outer ring of fire. This wouldn't be the first (or last) time a spacecraft imaged or attempted to image an eclipse, simulated or otherwise. In July 1975, the U.S. Apollo spacecraft attempted to block out the Sun while being photographed by their Soviet counterparts during the Apollo-Soyuz Test Project mission. However, this attempt to create an artificial eclipse had mixed results, as the Apollo spacecraft's thrusters in action disrupted the distribution of sunlight.

This Space Available hopes you enjoy tomorrow's eclipse safely and responsibly tomorrow! As for now, enjoy this walk down Skylab memory lane...

NASA MSFC photo: "This 1970 photograph shows the flight unit for Skylab's White Light Coronagraph, an Apollo Telescope Mount (ATM) facility that photographed the solar corona in the visible light spectrum. A TV camera in the instrument provided real-time pictures of the occulted Sun to the astronauts at the control console and also transmitted the images to the ground. The Marshall Space Flight Center had program management responsibility for the development of Skylab hardware and experiments." 
NASA image: "The solar corona and a solar prominence as seen through the White Light Coronagraph, Skylab Experiment S052, on Jan. 17, 1974. This view was reproduced from a television transmission made by a TV camera aboard the Skylab space station in Earth orbit. The bright spot is a burn in the vidicon. The solar corona is the halo around the sun which is normally visible only at the time of solar eclipse by the moon. The Skylab coronagraphy uses an externally-mounted disk system which occults the brilliant solar surface while allowing the fainter radiation of the corona to enter an annulus and be photographed. A mirror system allows either TV viewing of the corona or photographic recording of the image." This image was taken during the Skylab 4 mission.


NASA MSFC images, a solar eruption sequence recorded by Skylab: "Breaking the grip of the closed magnetic loops that constrain other gases around it, a spray of chromospheric material surges upward, free of the Sun. Views 1 through 5 were recorded about 5 minutes apart by Skylab and comprise a composite of separate images made in chromospheric (red), transition region (green), and coronal (blue) temperatures of an ultraviolet sequence that depicts a solar eruption. Eruption begins (view 2) as material in or near a small, compact loop develops enough energy to overcome the Sun's magnetic bonds." Images dated 1973, but this may be incorrect (if so feel free to correct me). 
NASA photo, dated Jan. 1974: "A 35mm camera, operated by astronaut William R. Pogue, Skylab 4 pilot, recorded this wide scene of his Skylab 4 crewmates on the other end of the orbital workshop. Astronauts Jerry P. Carr (right), commander, and Edward G. Gibson, science pilot, pose for the snapshot. Also in the frame are parts of three Extravehicular Mobility Unit (EMU) spacesuits, used on several EVA sessions during the third manning of the Skylab space station." In my humble estimation, this is one of the best Skylab photographs ever.
NASA photo, a master at work...on the ground: "Scientist-astronaut Edward G. Gibson, science pilot for the third manned Skylab mission (Skylab 4), enters a notation in a manual while seated at the control and display panel for the Apollo Telescope Mount (ATM) during simulations inside the one-G trainer for the Multiple Docking Adapter (MDA) at the Johnson Space Center (JSC)." Photo dated Sept. 10, 1973.