Update: NASA has postponed the Wallops launch until 8:02 p.m. on Friday May 14, writing:

"The Black Brant XII launch scheduled for May 12 has been postponed to provide time for inspection of the rocket after the vehicle came in contact with a launcher support during today’s preparations. The next launch opportunity is NET 8:02 pm ET, Friday, May 14."

That's the time window for NASA's latest rocket launch, which will see the U.S. space agency send a four-stage Black Brant XII sounding rocket up into the air as part of a mission called KiNet-X, designed to study how energy and momentum are magnetically connected through space.

Weather permitting, this event will put on a spectacular (albeit brief) show for people all along the Atlantic coast, most of the eastern United States, and parts of Canada, including Toronto.

Now's a good time to take a look at our vapor tracer thread, especially for those in Bermuda tonight! https://t.co/OZwR1pyIsN

— NASA Wallops (@NASA_Wallops) May 12, 2021

Here's what's going to happen:

About 10 minutes after the rocket leaves NASA's Wallops Flight Facility in Virginia, it will release a whole bunch of barium vapour just north of Bermuda.

The vapour is not harmful to the environment or public health, but it is quite colourful.

"Immediately after release of the vapor, the spherical clouds are a mixture of green and violet, but that phase only lasts about 30 seconds when the un-ionized component of the cloud has diffused away," explains NASA's Keith Koehler.

"After exposure to sunlight the vapour clouds quickly ionize and take on a violet colour."

As the violet lines diffuse and spread out, they'll become too thin to see with the naked eye, giving viewers only about 30 seconds to enjoy the phenomenon, which will either look like proper clouds or "short trails" depending on where they're watching from.

LAUNCH UPDATE 🚀 We're extending tonight's launch window, which now opens at 7:59 pm ET and runs through 8:53 pm. Clouds in Bermuda are a concern, but we're hoping for a break in the weather for our vapor tracer experiment. Live stream begins at 7:40 pm.https://t.co/94r0BlGfI6

— NASA Wallops (@NASA_Wallops) May 12, 2021

People in Bermuda are expected to get a full on "light show," says NASA, if the launch goes forward as planned (it's already been delayed three times due to poor weather conditions).

Everyone else should be able to see the vapour, but at different time intervals.

NASA has released a map showing how long after deployment people in different parts of North America can expect to see the barium clouds. Toronto is in the yellow "60-90 seconds" zone, but only just; viewers along the southern shores of Lake Ontario are in the purple "30-60 seconds" zone.

You can watch the mission live via the Wallops IBM video site beginning at 7:40 p.m. this evening — but don't forget to look up (and keep looking up) nine minutes after the launch!