The Tau Herculid Meteor Shower — Possible Outburst

May 25, 2022: In late 1995, Comet 73P/Schwassmann-Wachmann 3 exploded. Next week, some of the debris might hit Earth.


Above: NASA images of Comet 73P still crumbling years after its initial breakup. [more]

Multiple forecasters agree that a meteor shower could erupt on May 31, 2022, when Earth runs into one or more debris streams from Comet 73P. The display could be as intense as a meteor storm (1000 or more meteors per hour) or as weak as nothing at all. No one knows how much debris is inside the approaching streams, so meteor rates are hard to estimate.

Whatever happens, people in North America are in a good position to see it. Almost the entire continent will be in Moon-free darkness when the shower peaks. Maximum activity is expected around 1:00 am Eastern Daylight Time (05:00 UT) on Tuesday morning, May 31st. The shower’s radiant (the point from which all meteors stream) will be almost straight above Baja California.

Above: Altitude contours for the shower’s radiant. Baja California is favored with zenith observing geometry. Image credit: Josselin Desmars (IMCCE/IPSA) [more]

This isn’t the first time Earth has sampled debris from Comet 73P. In 1930, at least a handful of meteors were observed shortly after the comet’s discovery by German astronomers. The meteors emerged from a radiant near 4th magnitude star tau Herculis, so the shower has since been called “the tau Herculid meteor shower.” NASA cameras also detected minor tau Herculid activity in 2011 and 2017.

Based on past performance, the tau Herculids seem unlikely to produce a good show. For nearly a century the shower has been a dud. The X-factor this year is fresh material from the comet’s catastrophic breakup. If the new meteoroids reach Earth–and that is a big IF–shooting stars will fly from a point near the bright star Arcturus in the constellation Bootes. Here is a sky map to help you find it.

To learn more about the tau Herculid meteor shower, we recommend this comprehensive paper by Joe Rao, a lecturer at the Hayden Planetarium in New York. Also, a new analysis by Jérémie Vaubaillon of the Institute for Celestial Mechanics and Computation of Ephemerides in Paris raises the possibility of two additional outbursts on May 31st resulting from debris shed by Comet 73P in the years 1892 and 1897.

It all adds up to a date with the night sky at the end of the month. Don’t miss it!

A Mixed Up Sunspot

May 10, 2022: Sunspot AR3006 is having an identity crisis. It is supposed to have a +/- magnetic field. Mostly it does. But deep inside the sunspot’s primary core, the polarity is opposite: -/+. Note the circled region in this magnetic map of the sunspot from NASA’s Solar Dynamics Observatory:

The mixture of magnetic polarities makes this sunspot interesting and dangerous. When opposite polarities bump together, it can light the fuse of magnetic reconnection–the explosive power source of solar flares. If AR3006 flares today, it will be geoeffective. The sunspot is directly facing Earth.

Update: The sunspot *did* flare today. An X1.5 class explosion on May 10th (1355 UT) caused a radio backout over the Atlantic Ocean and may have hurled a complicated CME toward Earth. Solar flare alerts: SMS Text

A Tiger ELVE over Texas

May 2, 2022: For a few milliseconds last Thursday night, an enormous (100 km wide) red ring of light appeared over west Texas. Thomas Ashcraft photographed it from across the state line in New Mexico:

This is an “ELVE”–short for Emissions of Light and Very Low Frequency Perturbations due to Electromagnetic Pulse Sources. It’s a rare species of sprite discovered in 1990 by cameras onboard the space shuttle. Ashcraft may have just taken the best ever picture of one from the ground.

“The ELVE was generated by a super-strong lightning stroke that occurred over west Texas near the town of Borger at April 28 2022 0439:10.5326 UT,” says Ashcraft. “Note also the sprite elements at the bottom of the ELVE.”

The lightning bolt was so strong, it generated an intense electromagnetic pulse (EMP). The red ring marks the spot where the EMP hit Earth’s ionosphere. Normal lightning bolts carry 10 to 30 kilo-ampères of current; this bolt was about 10 times stronger than normal.

Above: A close-up view of the ELVE shows “tiger stripes” and sprites near the center of the ring.

“The lightning stroke that manifested this event registered on VLF radios at least as far away as Germany,” notes Ashcraft. “You can actually hear the lightning stroke in my video.”

Bonus: This is also a Tiger ELVE. Note the linear corrugations across the red ring. These are impressed on the ELVE by gravity waves in the upper atmosphere. Like a tiger, this ELVE has stripes.

Learn more about the history and physics of ELVEs here and here.