Green Comet Approaches Earth

On March 21st, Comet 252P/LINEAR will make a close approach to Earth–only 0.036 AU (5.4 million km) away. This is the fifth closest cometary approach on record and, as a result, the normally dim comet has become an easy target for backyard telescopes. Indeed, it is brightening much faster than expected.

“Comet 252P/LINEAR has surpassed expectations and is now bordering on naked eye visibility for southern observers,” reports Michael Mattiazzo of Swan Hill, Australia. “At the moment it is near magnitude +6,” Observing from Brisbane, Australia, Tom Harradine didn’t even need a telescope to photograph 252P/LINEAR. On March 17th, he caught the green comet (circled) passing by the Tarantula Nebula using just a digital camera:

“This image is a stack of 140 four second exposures I made using a Canon EOS 70D set at f/4.0, ISO 12800, and 200mm,” he says.

The comet is green because its vaporizing nucleus emits diatomic carbon, C2, a gas which glows green in the near-vacuum of space. The verdant color will become more intense in the nights ahead as 252P/LINEAR approaches Earth.

In recent days, astronomers have realized that Comet 252P/LINEAR might have a companion. A smaller and much dimmer comet named “P/2016 BA14” will buzz Earth even closer than 252P/LINEAR on March 22nd. P/2016 BA14 appears to be a fragment of 252P/LINEAR. Unlike its parent, however, P/2016 BA14 is “pitifully faint” and difficult to observe. Sky and Telescope has the full story.

There is a chance that the comet’s approach could cause a minor meteor shower. According to the International Meteor Organization, “[modeling by forecaster] Mikhail Maslov indicates that there might be a weak episode of faint, very slow meteors (15.5 km/s) on March 28–30 from a radiant near the star μ Leporis.” Little is known about meteors from this comet, so estimates of the meteor rate are very uncertain. Maslov’s models suggest no more than 5 to 10 per hour.

This is a southern hemisphere event. At closest approach on March 21st, 252P/LINEAR will speed through the constellations Triangulum Australis and Apus, far south of the celestial equator. Observers can use this ephemeris to point their cameras and telescopes.

Physics of an Exploding Space Weather Balloon

by Dr. Tony Phillips (

On Feb. 27, 2016, the students of Earth to Sky Calculus launched a space weather balloon to measure increasing levels of cosmic rays. At the apex of the flight, the balloon exploded as planned and the radiation sensors parachuted back to Earth. A high-speed camera on top of the payload captured some extraordinary images of the pop:

These images illustrate new findings about the physics of exploding balloons. In Oct. 2015, researchers Sébastien Moulinet and Mokhtar Adda-Bedia of the Ecole Normale Supérieure published a Physical Review Letter entitled “Popping Balloons: A Case Study of Dynamical Fragmentation.” In it, they reported the results of a series of fun yet informative laboratory experiments in which one balloon after another was popped and analyzed.

Basically, there are two ways a balloon can pop: along a single tear (the “opening regime”) or along many tears (the “fragmentation regime”). This video shows the two regimes in action. Which way the balloon decided to pop depends on the stress in the rubber membrane. When the stress is low, it can be relieved with a single tear, but when the stress is high, many tears are required to do the job.

Clearly, space weather balloons explode in the fragmentation regime. This is hardly a surprise. When space weather balloons are launched, they measure no more than 6 to 8 feet in diameter. By the time they reach the stratosphere, they have stretched into a sphere as wide as a house. That’s a lot of tension to release!

More information about this research is available from the American Physical Society.

Spherical Camera at the Edge of Space

On Feb. 27th, and the students of Earth to Sky Calculus launched a helium balloon to the stratosphere to monitor increasing levels of cosmic rays. In addition to radiation sensors, the payload carried something special: a spherical camera. Click and drag on the image below to explore California’s Sierra Nevada from an altitude of 115,300 feet–and don’t forget to look up at the balloon!

The camera, a Ricoh Theta S, will probably become a regular part of our cosmic ray payload. Imagery should improve in future flights as the students learn to lower the profile of the camera’s thermal pack–the strange-looking black object in the center of the 3D image. During its flight to the stratosphere, the camera experienced temperatures as low as -65 C. The thermal pack helps keep the camera’s batteries warm in these harsh conditions.

more spherical images: the students preparing to launch the balloon, the balloon ascending through clouds, the balloon exploding in the stratosphere.

Next week, the camera will take another trip–to Indonesia. The students will be using it to record a total eclipse of the sun on March 9th. Stay tuned for that!