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What are spring fireballs?

The rate of fireballs – or bright meteors – has been observed to go up in the Northern Hemisphere by as much as 30% from February through April. 2016 was a good year for spring fireballs. 2017, not so much.

View larger. | Photo taken March, 2016, by Mike Taylor in Maine.  Visit MikeTaylorPhoto.com

March fireball, captured in 2016 by Mike Taylor in Maine, against a backdrop of the aurora borealis.

In recent years, we’ve talked about the season of spring as being a good time to see especially bright meteors, aka fireballs. The story began with a 2011 report by NASA meteor expert Bill Cooke, who was quoted as saying:

Spring is fireball season. For reasons we don’t fully understand, the rate of bright meteors climbs during the weeks around the vernal equinox.

NASA said in 2011 that, in the weeks around the start of northern spring, the appearance rate of fireballs can increase by 10-30 percent.

2016 was apparently a good year for spring fireballs, according to a March 9, 2016 article by Vincent Perlerin of the American Meteor Society (AMS). Perlerin reported on six major fireball events over the U.S. between March 2 and March 8, 2016. He also wrote:

2016 seems to good year for fireballs. Since January 1st, 2016, the American Meteor Society has received more than 910 fireball reports through its online Fireball Report program. In comparison, only 839 have been received in 2015 during the same period (-8.5% compared to 2016). The 2016 reports have been linked to 49 fireball events with more than 10 reports, 25 events with more than 25 reports and 10 events with more than 50 reports (8 of these events have more than 100 reports).

In 2017, Robert Lunsford of the AMS told EarthSky that the time to watch for spring fireballs comes a month or so before the vernal equinox (around March 20-21 each year). He wrote:

[Spring fireballs] can be easily picked out from the list of events in our fireball table. I believe that there is no doubting the existence of these fireballs. They are the result of the antapex radiant being located at its highest point of the year in the the evening sky. I’m certain the same thing occurs in the southern hemisphere during the months of August through October. Unfortunately there are far fewer people to report them from down there. The overall results of the AMS fireball totals since 2005 display a spike in February, a month normally known for low meteor rates.

So spring fireballs – from, say, February to April in the Northern Hemisphere and from August to October in the Southern Hemisphere – may be caused by the fact that the antapex radiant lies highest above the horizon this time of year during the evening hours at these times. What is the antapex radiant? You might have heard the term apex of the sun’s way to describe the direction our sun is moving through space, with respect to the stars. Our sun and family of planets travel more or less toward the star Vega in the constellation Lyra; and that is the apex of the sun’s way. The antapex is the direction in space opposite the apex of the sun’s way; it’s the direction opposite our sun’s motion through space.

Fireball season ... via NASA

Fireball season … via NASA

A NASA website suggested:

The reason [for spring fireballs] is still unknown, but one hypothesis is that more space debris litters this section of Earth’s orbit.

Meteors are debris from space. They typically range in size from a few feet (about a meter) to smaller than a grain of sand. As these objects enter Earth’s atmosphere, they vaporize due to friction with the air.

NASA scientists at one time set up a network of ground cameras in order to track and record video of meteors flaming overhead. The footage could be used to pinpoint a meteor’s orbit and origin. The video below – which is from 2011 – explains more:

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Speaking of meteors, while spring might be the best time to see fireballs, major meteor showers – sometimes featuring a meteor or more every minute – take place throughout most of the year, with a break between the Quadrantids in early January and April’s Lyrid meteor shower.

The next regularly occurring, major meteor shower will be the Lyrids in April. In 2017, their expected peak is the morning of April 22.

Bottom line: In recent years, there’s been a discussion of the possibility of a spring fireball season. Apparently, in some years, the rate of fireballs – or bright meteors – in the Northern Hemisphere has been observed to increase by as much as 30% from February through about April (a similar increase might be expected from August to October in the Southern Hemisphere). 2016 seemed to be a good year for spring fireballs. 2017 … not so much.

Click here to see the dates of the major meteor showers.

Deborah Byrd

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