Daytime Arietid Meteor Shower

The Daytime Arietids are the strongest meteor shower of the year that almost nobody sees. In early June their radiant in Aries sits only about 30 degrees west of the Sun, so the shower is at its best in broad daylight. Radio and radar detect it easily, but your eyes can catch only a few of its meteors, in the last hour before dawn, when the radiant has just cleared the eastern horizon.

Where the meteors come from

The IAU Meteor Data Center lists Comet P/1999 J6 (SOHO) as the parent. The IMO calendar does not name one, so treat the link as likely rather than proven. The comet, found in images from the SOHO solar observatory, goes around the Sun about every 5.5 years on a very elongated orbit that takes it within about 7 million km of the Sun, far closer than Mercury. Its dust meets Earth at 38 km/s, a medium speed, but from a direction close to the Sun, so most of it strikes Earth's daytime side.

When to watch

The shower is listed as active from mid-May to late June, peaking around June 7 or 8. Radio counts show the main activity from late May to about June 20; the exact length is not well known, partly because the shower overlaps the Daytime Zeta Perseids. The table above gives the expected peak and the Moon, but for a daytime shower the hour matters less than usual.

Your window is short. The radiant rises roughly two hours before the Sun, which leaves about an hour before twilight washes out the fainter meteors. Watch on the mornings within a few days of the peak, from about 90 minutes before sunrise until the sky gets too bright.

How to find the radiant

The radiant is in Aries, a small constellation between the Pleiades and the Great Square of Pegasus. Its brightest star, Hamal, is a useful guide: the radiant lies about 10 degrees east of it, roughly one fist at arm's length, a little closer to the horizon. When the sky begins to brighten noticeably, the radiant is only about 10 degrees up in the east, from either hemisphere. You do not need to see it; just trace each meteor back toward Aries.

What to expect

The listed ZHR of 30 comes mostly from radio and radar, which count meteors day and night. With the radiant about 10 degrees up, you see only around a sixth of that even under a perfect sky, and twilight cuts it further. One to three Arietids in the hour before dawn from a dark site is realistic; from the suburbs you may see none. The meteors are of medium speed, but coming in at a low angle they often look long and leisurely. The population index of 2.8 points to a mix of faint and moderately bright meteors.

Viewing tips

• Check your sunrise time and be outside, facing east, about 90 minutes before it.
• Pick a spot with a clear, low eastern horizon, free of trees and town lights in that direction.
• Look 30 to 50 degrees up rather than at the horizon. Meteors from a low radiant travel a long way up the sky.
• To follow the whole shower, try radio. The IMO collects forward-scatter radio counts, which pick up daytime meteors around the clock.

History and notable displays

The daytime showers came to light almost by accident. During radar observations of the Eta Aquariids in May 1947, the team at Jodrell Bank in England, led by Bernard Lovell, left the equipment running after dawn and found that meteor echoes kept coming in daylight. More daytime streams turned up that summer and in the following years, including those described in a 1949 paper by Aspinall, Clegg and Lovell. Of these, the IMO rates the Arietids as the strongest. Today they are followed mainly by radio observers, and recent radio studies put the maximum about a day later than the date in the IAU list.