There’s a Meteor in My Image!

The night of August 16, 2019 UT, I was hoping to be the first person to record an occultation of a star by the asteroid 10373 MacRobert, named after Sky & Telescope senior editor Alan MacRobert. Alas, it was not to be, but I did receive a celestial consolation prize (or is that a constellation prize?) just as rare: a meteor! Here it is:

Kappa Cygnid recorded on 16 Aug 2019, 3:51:21.540 – 3:51:21.807 UT (0.267s, field size ~ 15′)

In the caption above, you’ll note that I stated this was a Kappa Cygnid meteor. How did I determine that?

The first step is to determine the direction the meteor traveled through the image. Since I have an equatorially-mounted telescope, north is always up and east is to the left, just like in the real sky. Using Bill Gray’s remarkable Guide planetarium software, which I always use when imaging at the telescope, I identified two stars (and their coordinates) very close to the path of the meteor across the field. The meteor flashed through the field so quickly that I am not able to determine whether the meteor was traveling from NNE to SSW or vice versa. But since I was imaging in Sagittarius, south of all the radiants active on that date, it is most likely that the meteor was traveling NNE to SSW. But, of course, it could have been a sporadic meteor coming from any direction, though as you will see, I think I can convincingly rule out that scenario.

The two stars very close to the meteor’s path were:

3UC 148-239423
α = 17h 56m 38.42s, δ = -16° 23′ 27.1″

3UC 147-243087
α = 17h 56m 31.96s, δ = -16° 30′ 40.0″

The right ascensions and declinations above are epoch of date.

Now, if this meteor came from a particular radiant, a great circle from the meteor shower radiant to either of the two stars (or the midpoint along the line connecting them) should be in the same direction as the direction between the two stars crossed by the meteor.

Meteor shower radiants drift from night to night as the Earth passes through the meteor stream due to its orbital motion around the Sun. We must find the radiant position for each meteor shower that was active on August 16, 2019 UT for that date.

Antihelion, South δ Aquariid, α Capricornid, and Piscis Austrinid meteor shower radiant drift
Source: International Meteor Organization, https://www.imo.net/files/meteor-shower/cal2019.pdf
Perseid meteor shower radiant drift
Source: International Meteor Organization, https://www.imo.net/files/meteor-shower/cal2020.pdf
Kappa Cygnid meteor shower radiant drift
Source: International Meteor Organization, https://www.imo.net/files/meteor-shower/cal2020.pdf

Looking at Table 6, Radiant positions during the year in α and δ, on p. 25 of the International Meteor Organization’s 2019 Meteor Shower Calendar, edited by edited Jürgen Rendtel, we find that four major meteor showers were active on August 16: the Antihelion source, which is active throughout the year (ANT), the Kappa Cygnids (KCG), the Perseids (PER), and the South Delta Aquariids (SDA). Though right ascension and declination for these radiants (presumably epoch of date) are not given specifically for August 16, we can interpolate the values given for August 15 and 20. Note that the right ascensions are given in degrees rather than in traditional hours, minutes, and seconds of time.

We are now ready to plug all these numbers into a SAS program I wrote that should help us identify the likely source of the meteor in the image.

The results show us that the Kappa Cygnids are the likely source of the meteor in the image, with a radiant that is located towards the NNE (15.8˚) from the “pointer stars” in our image, at a bearing that is just 3.7˚ different from their orientation.

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