2018 Daytime Arietids Peak June 10 as Invisible Yet Audible Shower

Summary: The 2018 Daytime Arietids peak Sunday, June 10, as a mostly invisible yet radio-audible meteor shower.

Shooting stars from Daytime Arietids appear to radiate from Aries the Ram constellation: Bob King @AstroBob_bk, via Twitter June 6, 2017

The 2018 Daytime Arietids, which shower mostly invisible yet radio-audible meteors between May 22 and July 2 each year, peak Sunday, June 10, at 22:07 Coordinated Universal Time (6:07 p.m. Eastern Daylight Time).

The Arietids occur as the strongest annual daytime shower. Their radiant in Aries the Ram constellation, however, renders them largely invisible. The radiant is a meteor shower’s apparent point of radiant in the sky.

Bruce McClure, EarthSky Tonight’s lead writer, notes the sun’s apparent passage in front of Aries occurs annually from about April 19 to May 14. In June, Aries is only about 30 degrees from the sun and, therefore, still within the sun’s glare.

Brief Arietid visibility is possible for Earth-based observers, though, because the radiant precedes sunrise by about 45 minutes. Peter Jenniskens, senior research scientist at SETI (Search for Extraterrestrial Intelligence) Institute’s Carl Sagan Center and meteor showers expert, points to the possibility of early morning observations, “in the hour before dawn,” during June’s first three weeks. Tony Phillips, formerly Science @NASA production editor and now Spaceweather.com’s science writer, explains that pre-dawn visibility is available to observers in both the Northern Hemisphere and the Southern Hemisphere.

For mid-northern latitudes, Phillips places the Daytime Arietid radiant at about 15 degrees above the eastern horizon at 5 a.m. on the date of the shower’s expected maximum, known as the peak date. Robert Lunsford, the American Meteor Society’s weekly Meteor Activity Outlook columnist, expects approximately six sporadic meteors per hour during pre-dawn’s last hour at rural sites at 45 degrees north latitude. Pre-dawn rates of nearly nine meteors per hour are suggested for rural sites at 25 degrees south latitude.

The radiant’s pre-dawn low altitude discourages vividly flaring, steep-angle entries into Earth’s upper atmosphere by Arietid particles. Instead, the shower tends toward producing nearly horizontal atmospheric skimmers. Known as Earthgrazers, the meteoroidal skimmers move slower than atmospheric meteors but streak brightly and lengthily.

Lunsford hypothesizes that, if the radiant were higher in the sky, Arietid visibility would rival that of August’s famous Perseids. Yet, Phillips considers the value of pre-dawn Arietid watches.

“Watching for early morning Arietids is a no-lose proposition,” Phillips says, “because, even if you don’t glimpse any meteors, you’ll be able to see the two bright planets Jupiter and Saturn less than 2 degrees apart rising above the eastern horizon.”

NASA’s Meteoroid Environment Office at Huntsville, Alabama’s Marshall Space Flight Center forecasts a maximum zenithal hourly rate (ZHR) of 74 meteors per hour for the Daytime Arietid shower’s peak date. The Arietids’ maximum ZHR rates as fourth in NASA’s 2018 list of 30 meteor showers. First place goes to the Geminids, with a maximum ZHR of 127 meteors per hour. The Quadrantids occupy second place, with a maximum ZHR of 120 meteors per hour. The Perseids claim third place, with a maximum ZHR of 106 meteors per hour.

The Meteoroid Environment Office assigns second place to the Daytime Arietids in its forecasted ranking of 2018’s six most active meteor showers in terms of flux. First place goes to January’s Quadrantids. July’s Southern Delta Aquariids, August’s Perseids, December’s Geminids and December’s Ursids hold third, fourth, fifth and sixth places, respectively.

Visual observation is not the only method for detecting the Daytime Arietid meteor shower. Radio astronomy identifies the Arietids as blips, reflected by meteor trails, as the shower’s particles hit Earth’s atmosphere at a velocity of 39 kilometers per second (87,000 miles per hour).

Phillips explains that as Daytime Arietid meteoroids “. . . move rapidly through the air, these specks of space dust heat and ionize the gas around them. During major meteor showers like the Arietids . . ., radio signals from TV stations, RADAR facilities, and AM/FM transmitters are constantly bouncing off these short-lived meteor trails.”

Radio astronomy, not observational astronomy, actually is credited with the Daytime Arietids’ discovery. Radio astronomy pioneers James Stanley Hey (May 3, 1909-Feb. 27, 2000) and G.S. Stewart discovered the mostly invisible yet radio-audible meteor shower in 1947 at Jodrell Bank Experiment Station (now Jodrell Bank Observatory), established on the University of Manchester’s Cheshire site.

The parent body for the Daytime Arietids is unknown. Proposed candidates comprise eccentric, near-Earth asteroid 1566 Icarus and short-period sungrazing comet 96P/Machholz. German astronomer Wilhelm Heinrich Walter Baade (March 24, 1893-June 25, 1960) discovered Icarus June 27, 1949, at Palomar Observatory, San Diego County, southwestern California. Using 29x130 binoculars, amateur astronomer Donald Machholz (born Oct. 7, 1952) discovered 96P/Machholz May 12, 1986, on central California’s Loma Prieta peak.

Peter Jenniskens profiles the Daytime Arietid meteor shower as having a breakup type of formation rather than the gas drag formation of gradual ejection by water vapor drag at perihelion (closest approach to the sun). He places the breakup formation date as around 1059 C.E.

The takeaway for the 2018 Daytime Arietids, which peak Sunday, June 10, is that the placement of the shower’s radiant near the sun accounts for mostly invisible shooting stars but does not prevent radio-audibility as blips reflecting Daytime Arietid meteor trails in the sky.

Canadian Meteor Orbit Radar (CMOR), a multi-frequency HF/ VHF radar, detects ablating meteoroids' ionized trails used to detect the ionized trails associated with ablating meteoroids; ARI=Daytime Arietids; DLT=Daytime lambda Taurids; JMC=June mu Cassiopeiids; ZPE=Daytime zeta Perseids: EarthSky @earthskyscience, via Twitter June 6, 2017

Acknowledgment

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

Image credits:

Shooting stars from Daytime Arietids appear to radiate from Aries the Ram constellation: Bob King @AstroBob_bk, via Twitter June 6, 2017, @ https://twitter.com/AstroBob_bk/status/872191946630062085

Canadian Meteor Orbit Radar (CMOR), a multi-frequency HF/ VHF radar, detects ablating meteoroids' ionized trails used to detect the ionized trails associated with ablating meteoroids; ARI=Daytime Arietids; DLT=Daytime lambda Taurids; JMC=June mu Cassiopeiids; ZPE=Daytime zeta Perseids: EarthSky @earthskyscience, via Twitter June 6, 2017, @ https://twitter.com/earthskyscience/status/872083253175386112

For further information:

Astro Bob (Bob King). “Arietid Meteor Shower Peaks -- Watch for Earthgrazers.” Area Voices. June 6, 2017.
Available @ http://astrobob.areavoices.com/2017/06/06/arietid-meteor-shower-peaks-watch-for-earthgrazers/

Bob King ‏@AstroBob_bk. “Arietid Meteor Shower Peaks -- Watch for Earthgrazers.” Twitter. June 6, 2017.
Available @ https://twitter.com/AstroBob_bk/status/872191946630062085

Byrd, Deborah. “This Week, a Daytime Meteor Shower.” EarthSky > Astronomy Essentials. June 6, 2017.
Available @ http://earthsky.org/astronomy-essentials/arietid-meteor-shower-daytime-june-peak

Dalbey, Beth. “Arietids Daytime Meteor Shower: How to See June 7 Peak.” Detroit Patch > Community Corner. June 6, 2017.
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EarthSky ‏@earthskyscience. "Daytime meteors in Arietid meteor shower! Will you see any? Maybe. Radar image via Canada’s Meteor Orbit Radar." Twitter. June 6, 2017.
Available @ https://twitter.com/earthskyscience/status/872083253175386112

Humanoid History @HumanoidHistory. “Asteroid 1566 Icarus near the Sun, drawn by David A. Hardy. At perihelion, it comes closer to the Sun than Mercury. Via @davidastrohardy.” Twitter. April 8, 2017.
Available @ https://twitter.com/HumanoidHistory/status/850800264764424192

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Jenniskens, Peter; Heather Duckworth; Bryant Grigsby. “Daytime Arietids and Marsden Sunskirters (ARI, IAU #171).” WGN: Journal of the International Meteor Organization, vol. 40, no. 3 (2012): 98-100.
Available @ http://cams.seti.org/jenniskens-ari_offprint.pdf

Kronk, Gary W. “Arietids.” Meteor Showers Online > Meteor Shower Calendar > June.
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Lunsford, Robert. “Meteor Activity Outlook for June 3-9, 2017.” American Meteor Society. June 1, 2017.
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Lunsford, Robert. “Meteor Activity Outlook for June 11-17, 2016.” American Meteor Society. June 10, 2016.
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Lunsford, Robert. Meteors and How to Observe Them. Astronomers’ Observing Guides. New York NY: Springer Science+Business Media, 2009.

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McClure, Bruce. “Aries? Here’s Your Constellation.” EarthSky > Astronomy Essentials > Constellations. Nov. 28, 2017.
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Ohtsuka, Katsuhito; Syuichi Nakano; Makoto Yoshikawa. “On the Association Among Periodic Comet 96P/Machholz, Arietids, the Marsden Comet Group, and the Kracht Comet Group.” PASJ Publications of the Astronomical Society of Japan, vol. 55, issue 1 (25 February 2003): 321-324. DOI: 10.1093/pasj/55.1.321. Tokyo, Japan: National Astonomical Observatory of Japan, 2003.
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Patel, Neel V. “You Can’t See the Arietid Daytime Meteor Shower But You Can Hear It Right Now.” Inverse Science. June 8, 2016.
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Phillips, Dr. Tony. “Daylight Meteors: The Arietids.” Spaceweather.com.
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Will Mysterious Gamma Delphinid Meteor Shower Shoot Stars Before 2027?

Summary: Will the mysterious Gamma Delphinid meteor shower, which was observed as an outburst June 10, 1930, shoot stars before its next outburst in 2027?

Gamma Delphinid meteor captured by two different all sky cameras in southern New Mexico, Tuesday, June 11, 2013: NASA’s Marshall Space Flight Center, CC BY NC 2.0 Generic, via Flickr

Will the mysterious Gamma Delphinid meteor shower, which announced its existence Tuesday, June 10, 1930, as a brief, brilliant outburst, shoot stars before its next projected outburst in 2027?

American astronomer Charles Pollard Olivier (April 10, 1884-Aug. 14, 1975) announced observation of the hithertofore unknown meteor shower in an article entitled “Meteor Notes” in the August-September 1930 issue of Popular Astronomy. Olivier had founded the American Meteor Society (AMS) in 1911 to promote visual study of random meteors and of meteor showers.

Paul S. Watson, a member of the American Meteor Society, reported the meteoric event to Olivier. Watson, along with co-observers Joseph Field and Frank Oertle, witnessed the outburst between 9:15 and 9:45 p.m. Eastern Standard Time, Tuesday, June 10, 1930 (2:15 to 2:45 a.m. Coordinated Universal Time, Wednesday, June 11, 1930), in Baltimore, Maryland.

The ”most unusual display” comprised 51 yellowish-white shooting stars. Despite the presence of a full moon and the shower’s brief duration, the shooting stars shone brightly. The trio’s report placed 39 at magnitude 1 and 10 at magnitude 0.

Watson’s report to Olivier identified the radiant, or apparent point of origin, for the meteor shower as tracing back to within 3 degrees of Gamma Delphini (γ Del; Gamma Del; γ Del) in Delphinus the Dolphin constellation. In his announcement in “Meteor Notes,” Olivier gave a rough calculation of 12 degrees above the horizon for the altitude of Gamma Delphini, as viewed at Baltimore, Maryland, at the time of the outburst. With the width of one fist, held at arm’s length, measuring approximately 10 degrees, Gamma Delphini’s altitude of 12 degrees equals about one and one-eighth fist widths above the horizon.

Meteor shower namesakes reflect the bright star or constellation nearest to the radiant at the shower’s peak. With a radiant near Gamma Delphini, Delphinus the Dolphin constellation’s third brightest star, the June 10, 1930, outburst is known as the Gamma Delphinid meteor shower.

Olivier reported the lack of meteors that night from his location, distanced about 100 miles northeast of Baltimore. Olivier’s outdoor observation point was on the grounds of Flower Observatory, where he served as the observatory’s fourth director for almost 25 years.

Located in Upper Darby Township, Delaware County, in southeastern Pennsylvania, Flower Observatory yielded good meteor viewing conditions June 10, 1930. Olivier noted in his announcement: “That same night was one of the most transparent we have had at Flower Observatory.”

Olivier unsuccessfully scanned the skies for about half an hour, beginning at 9:45 p.m. EST (2:45 UTC). University of Pennsylvania Astronomy Professor Samuel G. Barton, who was stationed indoors that night at the observatory’s 18-inch refracting telescope, made several 10 to 15 watches outdoors, with one preceding Olivier’s 9:45 p.m. start time. He also saw no meteors.

Eight and one-third decades later, a return outburst of the Gamma Delphinid meteor shower was projected for Tuesday, June 11, 2013. The geographic region of visibility favored the Americas.

American Meteor Society member Robert Lunsford pointed observers at mid-northern latitudes to Gamma Delphini’s June rising in the east after dusk. Earliest visibility was timed to Delphinus the Dolphin constellation’s appearance above the horizon.

In a live web chat beginning Monday, June 10, at 11 p.m. EDT (3 a.m. UTC, Tuesday, June 11), William “Bill” Cooke, program manager of NASA’s Meteoroid Environments Office at the Marshall Space Flight Center, gave easy viewing guidance. “Lie flat on your back and look straight up, 3:30-5:30 Eastern Time,” Cooke explained.

The moon, thin-slivered in its waxing crescent phase, offered no competition. Also, the moon exited early from the night sky, with moonset Tuesday, June 11, at 10:28 p.m. Eastern Daylight Time (2:28 a.m. UTC, Wednesday, June 12).

Peter Jenniskens, a Dutch and American astronomer and research scientist at NASA Ames Research Center and SETI (Search for Extraterrestrial Intelligence) Institute, and Esko Lyytinen, a Finnish mathematician and researcher, calculated a peak time of 4:30 a.m. EDT (8:30 a.m. UTC) for the June 11 display. They based their calculations upon the premise of an unknown, long-period comet, with an orbital period of more than 200 years, as the Gamma Delphinids’ parent body. Another important premise was the accuracy of nearness to Gamma Delphini as the reported radiant.

Unfortunately, the 2013 display was not a re-enactment of the 1930 outburst. Alan Boyle, MSNBC’s science editor, wrote on his website, Cosmic Log, that Bill Cooke described the faint event as a “very minor shower -- but that's why we look, right?”

Yet, stationed at geographical coordinates 35.50 north longitude, 105.89 west latitude, near Eldorado, north central New Mexico, natural phenomena videographer Thomas Ashcraft posted on Vimeo his capture of a "possible Gamma Dolphinid fireball." The impressive fireball flared Tuesday, June 11, at 2:38 a.m. Mountain Daylight Time (4:38 a.m. EDT; 8:38:34 UTC), only two minutes before the projected peak time.

Jenniskens and Lyytinen also have projected a possible outburst for June 2027. Although the Gamma Delphinid meteor shower’s parent body is unknown, the team’s premise of a long period comet is based upon the descriptions from the 1930 display.

The Gamma Delphinid meteor shower’s near-radiant, Gamma Delphini, is actually a binary star system comprising a yellow-white dwarf orbited by an orange subgiant. The fifth magnitude dwarf and fourth magnitude subgiant join Delphinus the Dolphin constellation from a distance of 104 light years. The duo also participates in the Dolphin’s diamond-like asterism, Job’s Coffin.

The takeaway for the elusive, hoped-for outburst of the mysterious Gamma Delphinid meteor shower is that observation, by experts as well as citizen scientists, will reveal whether the Gamma Delphinids shoot stars, faintly or dramatically, before 2027.

"Probable Gamma Delphinid Fireball Tuesday, June 11, 2013," from Thomas Ashcraft on Vimeo.

Acknowledgment

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

Image credit:

Gamma Delphinid meteor captured by two different all sky cameras in southern New Mexico, Tuesday, June 11, 2013: NASA’s Marshall Space Flight Center, CC BY NC 2.0 Generic, via Flickr @ https://www.flickr.com/photos/nasamarshall/9013480432/

Thomas Ashcraft, "Probable Gamma Delphinid Fireball June 11, 2013," via Vimeo June 11, 2013, @ https://vimeo.com/68139353

For further information:

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Available via VIMEO @ https://vimeo.com/68139353

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