The Iota Aquariids meteor shower
Key facts
- Peak
- Southern branch around 4–5 August; Northern branch around 20 August
- Active
- late July to late August
- Rate at peak (ZHR)
- about 2 for each branch
- Speed
- about 34 km/s
- Radiant
- Aquarius (two radiants, the southern one near Iota Aquarii)
- Parent body
- Unknown; now usually counted as part of the Antihelion Source
Dates shift slightly from year to year. This year's peak is in the events calendar, and the meteor-shower planner shows how high the radiant climbs from where you live, night by night.
The Iota Aquariids are two weak streams, a southern branch and a northern branch, that were long listed among the summer meteor showers of Aquarius. Today they are best known as an example of how meteor science decides what counts as a shower.
The Aquarius showers. In late July and August, Earth passes several streams whose radiants lie in or near Aquarius, the Water Carrier. The strongest is the Southern Delta Aquariids, with a peak rate of about 25 an hour. Next to it, observers in the twentieth century listed the Northern Delta Aquariids and the Southern and Northern Iota Aquariids, each producing only a few meteors an hour. Because their radiants were close together and their rates so low, separating them by eye was very difficult.
Southern and northern branches. The Southern Iota Aquariids were listed with a peak around 4–5 August and a radiant near Iota Aquarii. The Northern Iota Aquariids were weaker, with a peak usually given around 20 August, though different studies placed it anywhere from about 19 to 24 August. Both produce medium-slow meteors.
A change of view. Video networks, which measure the orbit of each meteor, found that much of this activity matches the Antihelion Source, the broad region of radiants opposite the Sun that supplies meteors all year. Observers now count both Iota Aquariid branches, along with the Northern Delta Aquariids, as part of that source. The Southern Delta Aquariids remain a separate, well-defined shower.
What to expect. A meteor or two an hour that seem to come from Aquarius, mixed with Southern Delta Aquariids and Alpha Capricornids, and often outnumbered by Perseids.
Viewing. Aquarius is low in the south from the UK in August, best around 1 to 3 am. From the tropics and the southern hemisphere it is high and well placed.
Viewing tips
- Watch after midnight, when Aquarius is highest in the south.
- Plot meteors on a star chart if you want to separate the Aquarius radiants.
- Expect most Aquarius meteors in late July to be Southern Delta Aquariids.
- Note that fast meteors from the north-east in August are almost certainly Perseids.
- Observe from the southern hemisphere or the tropics for a much higher radiant.