2018 October Delta Aurigids Peak Midnight to Pre-Dawn Thursday, Oct. 11

Summary: The 2018 October Delta Aurigids peak midnight to pre-dawn Thursday, Oct. 11, as a little-known, minor annual meteor shower.

The radiant, or apparent point of origin, for October Delta Aurigids lies in Auriga the Charioteer constellation, south of Delta (δ) Aurigae (top center): Sky & Telescope magazine (Roger Sinnott and Rick Fienberg), CC BY 4.0 International, via the International Astronomical Union

The 2018 October Delta Aurigids peak midnight to pre-dawn Thursday, Oct. 11, as a little-known minor annual meteor shower that was discovered and named in the late 20th century.

The International Meteor Organization’s 2018 Meteor Shower Calendar recommends peak date skywatching after local midnight for October Delta Aurigid observers. The calendar’s compiler, Dr. Jürgen Rendtel of northeastern Germany’s Leibniz Institute for Astrophysics Potsdam (AIP), describes the October Delta Aurigids as “visible chiefly from the northern hemisphere.”

The 2018 October Delta Aurigids encounter no interference from the moon for visibility on the shower’s peak date. The moon rises and sets as a daytime moon. Also, the moon’s entrance into its new phase Tuesday, Oct. 9, would promise invisibility if the moon were a nighttime presence during the 2018 October Delta Aurigid peak.

A zenithal hourly rate of two shower members per hour is predicted for the 2018 October Delta Aurigids. The zenithal hourly rate (ZHR) references ideal observable rates under optimal conditions.

Robert Lunsford, American Meteor Society’s Meteor Activity Outlook weekly columnist, describes the October Delta Aurigid shower’s meteors as swift movers. He clocks their entry velocity as 64 kilometers per second (40 miles per second).

The incomplete profile for the newly discovered autumnal shower offers possible activity dates that generally fall within the first half of October. Since 2011, the International Meteor Organization’s meteor shower calendars have identified annual activity dates of Oct. 10 to Oct. 18. Dr. Bill Cooke, lead of NASA’s Meteoroid Environment Office (MEO), gives activity dates of Sept. 20 through Oct. 16. American amateur astronomer Gary W. Kronke’s Meteor Showers Online website dates activity in the interval between Sept. 22 and Oct. 23.

The moon phases are mainly conducive for viewing the 2018 October Delta Aurigids, not only on peak date, but also for most of the shower’s October activity dates. The IMO’s range of Wednesday, Oct. 10 to Thursday, Oct. 18, finds day moons that set before prime viewing between local midnight and pre-dawn.

The 2018 opening activity date’s new moon transitions to the waxing crescent phase Thursday, Oct. 11. The first quarter phase takes over Tuesday, Oct. 16, with surface visibility of the lunar disk at 48 percent. The IMO-identified closing date, Thursday, Oct. 18, increases to 67 percent surface visibility as a waxing gibbous moon. And yet, the phase’s surface visibility does not matter because of the moon’s absence from the nighttime sky during the hours that are conducive to proper observation of the 2018 October Delta Aurigids.

Credit for discovery of the October Delta Aurigids goes to Jack D. Drummond of New Mexico State University, Robert K. Hill of National Radio Astronomy Observatory in Socorro, New Mexico, and Herbert A. Beebe of New Mexico State University. The 1979 discovery occurred during a review of 13 meteors that were doubly photographed between Oct. 25, 1976, and Dec. 13, 1977, at the NASA-NMSU Meteor Observatory in southern New Mexico. The trio noted two meteors, photographed Oct. 13, and Oct. 18, 1977, as a “matching pair” with similarities, such as retrograde orbits and respective velocities of 62.9 and 62.5 kilometers per second (39.08 and 38.8 miles per minute).

Drummond, Hill and Beebe pinpointed the apparent point of origin, known as the radiant, for the two similar meteors as near Delta Aurigae (δ Aur, δ Aurigae) in Auriga the Charioteer constellation. Its location south of Delta Aurigae places the radiant at maximum at 5 degrees northwest of Capella (Alpha Aurigae, α Aurigae; Alpha Aur, α Aur), according to American amateur astronomer Robert Lunsford. Capella’s star system of two binary pairs shines as the Charioteer’s brightest star, the Northern Celestial Hemisphere’s third brightest and the night sky’s sixth brightest star.

The October Delta Aurigids stream from an unknown parent body. Drummond hypothesizes an unknown comet with a short-period (115 years), retrograde orbit. Dr. Jürgen Rendtel of northeastern Germany’s Leibniz Institute for Astrophysics Potsdam (AIP) suggests a similarity in eccentricity and inclination with the orbits of Kreutz-group comets. He notes that Kreutz-group cometary orbits are evaluated as “end-states of orbital evolution.”

The takeaway for the 2018 October Delta Aurigids’ midnight to pre-dawn peak Thursday, Oct. 11, is that the minor shower, recently discovered and named in the late 20th century, features swift movers from an unknown parent body.

Praja, or Prajapati (Delta Aurigae), nearest star to October Delta Aurigid radiant, perches at the apex of triangle formed with Auriga the Charioteer’s two brightest stars, Capella and Menkalinan: Petr Kocna, CC BY ND 3.0 Unported, via Univerzita Karlova 1. Lékařská Fakulta

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

The radiant, or apparent point of origin, for October Delta Aurigids lies in Auriga the Charioteer constellation, south of Delta (δ) Aurigae (top center): Sky & Telescope magazine (Roger Sinnott and Rick Fienberg), CC BY 4.0 International, via the International Astronomical Union @ https://www.iau.org/public/themes/constellations/

Praja, or Prajapati (Delta Aurigae), nearest star to October Delta Aurigid radiant, perches at the apex of triangle formed with Auriga the Charioteer’s two brightest stars, Capella and Menkalinan: Petr Kocna, CC BY ND 3.0 Unported, via Univerzita Karlova 1. Lékařská Fakulta @ http://www1.lf1.cuni.cz/~kocna/stars01.htm (image specific URL @ http://www1.lf1.cuni.cz/~kocna/ha118358.jpg)

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