In November and December 2011, professional and amateur astronomers revelled in observing a sun-grazing comet that dove close to the Sun and survived for a return flight back to the outer solar system. Astronauts on the International Space Station (ISS) enjoyed their own surreal view of the comet as it appeared on Earth’s horizon on the day of the solstice.
ISS Commander Dan Burbank captured a series of digital photographs of Comet Lovejoy on December 21, 2011, as it rose above Earth’s limb. The ISS was passing from eastern Australia southeast toward New Zealand, between 17:35:50 to 17:43:02 Universal Time (6:35 to 6:43 a.m. local time on December 22). Those still images were compiled into a time-lapse video that you can view here. In an interview with WDIV-TV, Burbank described the moment as “the most amazing thing I have ever seen in space.”
Note how the tail of the comet points away from the Sun even as the comet itself is moving in the same direction, away from our star. Every comet has two tails, one of ice and dust, the other of ions, or charged particles. The heat and pressure of sunlight sloughs off the ice and dust, pushing it away from the Sun. Likewise, the solar wind strips ions off of the comet surface, though not necessarily in the same direction as the tail of debris and ice. The ion tail is not visible in this image.
The comet, officially designated C/2011 W3 (Lovejoy), was discovered by Australian amateur astronomer Terry Lovejoy on November 27, 2011. It belongs to a group of comets known as the Kreutz sungrazers, which are thought to be pieces of a much larger comet that broke up centuries ago. The comets are termed sungrazers because their orbits take them quite near—and often into—the Sun.
In the ISS image above, you can also see green and yellow airglow paralleling the Earth’s horizon line (or limb) before it is overwhelmed by the light of the rising Sun. Airglow is the emission of light by atoms and molecules in the upper atmosphere after they are excited by ultraviolet radiation. In the video, small intermittent flashes of white lightning discharges also are visible over Earth’s surface.
Astronaut photograph ISS030-E-015491 was acquired on December 22, 2011, with a Nikon digital camera, and is provided by the ISS Crew Earth Observations experiment and Image Science & Analysis Laboratory, Johnson Space Center. The image was taken by the Expedition 30 crew. The image has been cropped and enhanced to improve contrast. Lens artifacts have been removed. The International Space Station Program supports the laboratory as part of the ISS National Lab to help astronauts take pictures of Earth that will be of the greatest value to scientists and the public, and to make those images freely available on the Internet. Additional images taken by astronauts and cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of Earth by Michael Carlowicz, NASA Earth Observatory, and Melissa Dawson and William L. Stefanov, Jacobs/ESCG at NASA-JSC at NASA-JSC.