The Southern Delta Aquariids meteor shower
Key facts
- Peak
- around 30–31 July
- Active
- about 12 July to 23 August
- Rate at peak (ZHR)
- about 25
- Speed
- 41 km/s
- Radiant
- Aquarius (near the star Delta Aquarii)
- Parent body
- Uncertain; probably linked to Comet 96P/Machholz
Dates shift slightly from year to year. This year's peak is in the events calendar.
The Southern Delta Aquariids are the quiet companion of the Perseids. They peak in late July, while the Perseids are building up, and anyone watching on a summer night may see meteors from both showers at once. Learning to tell them apart is a good test of a meteor watcher's skills.
The shower takes its name from Delta Aquarii, a star in the constellation of Aquarius near the radiant. The word "Southern" is there because astronomers once recognised a weaker Northern branch as well. The Northern Delta Aquariids are now considered too faint to count as a significant shower, so in practice "Delta Aquariids" usually means the southern stream.
The parent body. Unlike most major showers, the Delta Aquariids have no single confirmed parent. The leading idea is that they are linked to Comet 96P/Machholz, a short-period comet with an unusual orbit that brings it very close to the Sun. This comet seems to belong to a family of related objects, including some small sungrazing comets, that may have come from the break-up of a larger body long ago. The Delta Aquariid stream may be debris from that same family. Because the evidence is indirect, it is fairest to say the parent is probably, rather than certainly, 96P/Machholz.
What to expect. Delta Aquariids are medium-speed meteors, entering the atmosphere at about 41 km/s. Most are faint, and the shower has a broad, gentle peak rather than a sharp spike, so several nights around the end of July give similar rates. Under very dark skies in the southern hemisphere you might see 15 to 20 an hour, sometimes more. The shower is active for weeks, so a few stragglers continue well into August.
Telling them from Perseids. Trace a meteor's path backwards across the sky. Delta Aquariids point back to Aquarius, low in the south, while Perseids point back to Perseus in the north-east. Delta Aquariids also tend to be slower and fainter than the swift, often bright Perseids.
Viewing from the UK. From Britain the radiant stays low in the southern sky, so many meteors are lost below the horizon, and the short summer nights limit the hours of true darkness. In the north of Scotland the sky barely darkens at all in late July. Even so, a patient observer in southern England with a clear southern horizon can expect a few an hour in the early hours, around 1 to 3 a.m. Combine your watch with the rising Perseids for a busier night.
Viewing worldwide. The Delta Aquariids are much better from the southern hemisphere and the tropics, where Aquarius climbs high overhead and the winter nights are long. Observers in Australia, South America and southern Africa see the shower at its best. In the northern hemisphere, the further south you are, the better: the southern United States and the Mediterranean do far better than northern Europe.
The Moon's phase can make or break this faint shower, so check it before planning a night out. Peak dates vary slightly from year to year.
Viewing tips
- Look towards the south, where the radiant in Aquarius sits low in the UK sky.
- Watch in the early hours, roughly 1 to 3 a.m., when the radiant is highest.
- Trace each meteor backwards to tell Delta Aquariids from Perseids.
- Pick a moonless night, because most Delta Aquariids are faint.
- Use the same night to watch for early Perseids, which are building up at the same time.
Read about the parent: Comet Machholz, and the other comets behind meteor showers.