Dust from Halley's comet
The Eta Aquariids come from comet 1P/Halley. Each time the comet comes near the Sun it sheds ice and rock, and the dust becomes the Eta Aquariids in May and the Orionids in October. Halley takes about 76 years to orbit the Sun. Casual observers last saw it in 1986, and it returns to the inner solar system in 2061.
Edmond Halley identified the comet in 1705 and predicted its orbit. It also appears on the Bayeux Tapestry, which depicts the Battle of Hastings in 1066. The nucleus measures 16 by 8 by 8 kilometers, and its albedo is 0.03, which makes it one of the darkest objects in the solar system.
A shower for the south
The radiant is in Aquarius, near Eta Aquarii, one of the four stars of the "water jar." That star and that constellation give the shower its name, but Aquarius is only a pointer. The meteors come from Halley's dust.
The meteors are fast, at about 65.4 kilometers a second, and leave glowing trains that last seconds to minutes. NASA says the Southern Hemisphere is the better place to watch, because Aquarius sits higher in the sky there. From the north the rate drops to about 10 an hour, and the meteors that do show are often Earthgrazers, long streaks that skim the horizon.
Records back to 74 BCE
Wikipedia lists records of outbursts in 74 BCE and many centuries since, the latest in 934. The Eta Aquariids were the first shower linked to Halley's Comet. The comet's current orbit doesn't pass close enough to Earth to be the source, so the meteoroids separated from it long ago.
Sato and Watanabe attributed the meteoroids in 2013 to a very old ejection from Halley that sits in resonance with Jupiter's orbit, the same mechanism seen in the Orionids.
The next 8 years
The peak is when Earth passes the densest part of the stream, and it falls on almost the same date each year. What changes is the Moon. The table shows the Moon at the peak and how many hours of dark, moon-free sky there are with the radiant above 20 degrees, on the better of the two nights around the peak.
| Year | Peak | Moon at the peak | Good hours, 40 N | Rating, 40 N | Good hours, 30 S | Rating, 30 S |
|---|---|---|---|---|---|---|
| 2027 | May 6, 2027, 15:11 UTC | 0% (new Moon) | 0.0 h | No dark window | 2.2 h | Good |
| 2028 | May 5, 2028, 21:20 UTC | 89% (waxing gibbous) | 0.0 h | No dark window | 2.2 h | Good |
| 2029 | May 6, 2029, 03:29 UTC | 43% (waning crescent) | 0.0 h | No dark window | 0.0 h | No dark window |
| 2030 | May 6, 2030, 09:38 UTC | 12% (waxing crescent) | 0.0 h | No dark window | 2.2 h | Good |
| 2031 | May 6, 2031, 15:47 UTC | 100% (full Moon) | 0.0 h | No dark window | 0.0 h | No dark window |
| 2032 | May 5, 2032, 21:57 UTC | 16% (waning crescent) | 0.0 h | No dark window | 0.2 h | Poor |
| 2033 | May 6, 2033, 04:06 UTC | 49% (first quarter) | 0.0 h | No dark window | 2.3 h | Good |
| 2034 | May 6, 2034, 10:15 UTC | 92% (waning gibbous) | 0.0 h | No dark window | 0.0 h | No dark window |
Good hours are measured in local solar time and count only times when the Sun is more than 18 degrees below the horizon, the Moon is below the horizon and the radiant is above 20 degrees. Rating: 4 hours or more is excellent, 2 to 4 good, under 2 poor. Peak times are in UTC.
The best and worst year
From 40 degrees north the best of these years is 2027, with 0.0 good hours and the Moon 0% lit at the peak. The worst is 2027, with 0.0 good hours. From 30 degrees south the best is 2033, with 2.3 good hours.
The night of the next peak at 40 degrees north
The better night around the May 6, 2027 peak starts on the evening of May 5, 2027. Times are local solar time.
| What | Local solar time |
|---|---|
| Astronomical darkness | 20:45 to 03:10 |
| Moon above the horizon during the dark hours | none |
| Radiant above 20 degrees during the dark hours | none |
| Good window: dark, no Moon, radiant up | none |
The radiant sits at declination -1 degrees and right ascension 22.5 hours. Rating for that night: no dark window, with 0.0 good hours.
What the Eta Aquariids are
The parent is comet 1P/Halley. Halley's Comet. The Orionids in October come from the same comet. NASA says about 50 meteors an hour can be seen at the peak, and about 10 an hour from the Northern Hemisphere.
The Southern Hemisphere is the better place to watch, because the radiant sits higher in the sky there.
The shower is named after Aquarius, where the radiant lies near the star Eta Aquarii. The constellation only helps you find the radiant. It isn't the source of the meteors.
Meteor shower calendarEvery major shower with the Moon at its peak.
Sky calendarEclipses, planets and meteor showers.
Milky Way seasonThe best nights for the galaxy, park by park.Questions people ask
When do the Eta Aquariids peak?
The next peak is May 6, 2027 at about 15:11 UTC. The shower is active 19 April to 28 May.
How many Eta Aquariids can you see an hour?
The ZHR, an ideal rate under perfect skies with the radiant overhead, is 50. NASA says about 50 meteors an hour can be seen at the peak, and about 10 an hour from the Northern Hemisphere.
Will the Moon spoil the Eta Aquariids next time?
At the next peak the Moon is 0% lit (new Moon). From 40 degrees north that gives 0.0 dark, moon-free hours with the radiant up on the better night.
Which year is best for the Eta Aquariids?
Of the next 8 years, 2027 has the least moonlight problem at 40 degrees north, with 0.0 good hours.
Broad, steady and southern
There's no sharp peak. The shower has a broad maximum of good rates lasting about a week around 5 May. In 2013 the rate ran well above average for about 2 days, peaking at a ZHR of 135. Apart from that, activity is steady from year to year.
Wikipedia ranks it as the third strongest annual shower, usually 2 to 3 times stronger than the Orionids. The peak rate is about a meteor a minute, but northern observers rarely see it because the radiant stays low, and the best viewing is from the equator to 30 degrees south.
Watching the Eta Aquariids
Both hemispheres can see the shower in the pre-dawn hours. Lie with your feet facing east and let your eyes adapt. The shower runs 19 April to 28 May, so the peak night isn't the only chance.
The next peak is May 6, 2027, with the Moon 0% lit (new Moon). At 40 degrees north, none of the 8 peaks from 2027 to 2034 gives four moon-free hours with the radiant up. The best is 2027, with 0.0. The Moon is under a quarter lit at the peak in 2027, 2030 and 2032. It's three-quarters lit or more in 2028, 2031 and 2034, and in those years only the brightest meteors show.
From the south the radiant is higher before dawn. At 30 degrees south, none of the 8 peaks from 2027 to 2034 gives four moon-free hours with the radiant up. The best is 2033, with 2.3.
Two numbers for one shower
NASA's fast facts give about 10 meteors an hour under dark skies, and its main text says about 50 at the peak. The International Meteor Organization lists a ZHR of 50.
The larger figures are for the south, with perfect skies. For most of the world north of the equator, plan on a handful of meteors an hour in the hour before dawn, which makes the shower a modest return for an early alarm.
The Southern Delta Aquariids follow in July, and the meteor shower calendar shows both with the Moon.
Who's under the peak
The calculated peak is May 6, 2027 at 15:11 UTC. In local solar time that's the middle of the night (10 p.m. to 3 a.m.) for Beijing and Sydney, and evening, dawn or daytime for London, New York, Los Angeles, Sao Paulo, Johannesburg and Delhi.
The hour of the peak moves from year to year, because a calendar year isn't a whole number of Earth orbits. Across 2027 to 2034 it ranges from 03:29 to 21:57 UTC, so the part of the world that sits under the peak changes with it.