Eye on the sky
Rare planetary nebula Abell 78 glows as it reawakens as a so-called ‘born again’ star
HUBBLE SPACE TELESCOPE & PAN-STARRS, 15 MARCH 2021
We can’t blame William Herschel, who first coined the term in the 1780s, but ‘planetary nebula’ is a confusing misnomer. They have nothing to do with planets, but as he had recently also discovered Uranus (which he initially called a comet and a ‘nebulous star’), it’s understandable that Herschel conflated these hazy, disc-like objects with gas giant planets.
Planetary nebulae, like the Crab and the Dumbbell, are in fact the death throes of a star which, having exhausted the nuclear fuel at its core, collapses. Its shrugged-off outer layers create a diffuse gas shell, lit from within by a newly formed white dwarf.
Abell 78, however, is unusual. Found 5,000 lightyears away in Cygnus, it’s a rare ‘born-again’ planetary nebula. While it has a hydrogen-poor centre, the blue filaments show that hydrogen is so dense in its outer layers that nuclear fusion has fleetingly restarted – the final gasp of the dying star.
J-P METSAVAINIO, MARCH 2021
This extraordinary 234-panel high-resolution mosaic of the Milky Way was started by Finnish visual artist and astrophotographer J-P Metsavainio in 2009 and took almost 12 years to complete. About 100,000 pixels wide and capturing 125˚ of sky from the constellations of Taurus, the Bull (left) to Cygnus, the Swan (right), it shows an estimated 20 million individual stars. This Herculean effort called for over 1,250 hours of exposure time, including 100–plus hours on some of the dimmest supernova remnants.
TIANWEN-1, 4 MARCH 2021
This is one of the first highdefinition pictures returned by China’s Tianwen-1 robotic probe. Currently in orbit above Mars, its seven mission payloads are performing scientific tasks and analysing the surface for potential landing sites for its landing capsule. The capsule is due to be deployed this month, becoming the sixth rover to ever land on the Red Planet (after Sojourner, Opportunity, Spirit, Curiosity and Perseverance).