The Sigma Hydrids meteor shower

Key facts

Peak

around 7–9 December

Active

early to mid-December

Rate at peak (ZHR)

about 3–7

Speed

58 km/s

Radiant

Hydra (near the head of the Water Snake, close to the star Sigma Hydrae)

Parent body

Possibly comet C/2023 P1 (Nishimura)

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 Sigma Hydrids are a fast December shower radiating from the head of Hydra, the Water Snake. They are active in the week before the Geminids and have recently been linked to a comet that was easy to see in 2023.

History. The shower was first identified around 1960 by Richard McCrosky and Annette Posen, who searched photographs of meteors taken by the Harvard Meteor Program in the United States for groups with matching orbits. Video networks have since confirmed it as a regular annual shower.

The parent. For decades no parent was known. In August 2023 the Japanese amateur astronomer Hideo Nishimura discovered a comet with a camera and telephoto lens. Comet C/2023 P1 (Nishimura) brightened enough to be seen with binoculars and, by some, with the naked eye in September 2023, low in the twilight sky shortly before it passed close to the Sun. Calculations of its orbit showed a close match with the Sigma Hydrids. The comet takes several centuries to orbit the Sun. The link is likely but still being tested.

The radiant. Hydra is the largest constellation in the sky. Its head, a small group of stars south of Cancer and east of Procyon, contains Sigma Hydrae. The radiant lies close to the celestial equator and rises in the late evening.

What to expect. Around three to seven meteors an hour at the peak, around 7–9 December. They are fast, at about 58 kilometres per second, and many are faint. A fast meteor from the area east of Procyon in early December may be a Sigma Hydrid; Geminids from nearby Gemini are much slower.

Viewing. The shower is visible from both hemispheres. From the UK the radiant is highest in the south in the hours before dawn. Southern observers see it high in the north.

Viewing tips

1. Watch in the hours before dawn, when Hydra's head is high in the south.
2. Find the small ring of stars below Cancer that forms the Snake's head.
3. Separate them from Geminids by speed: Sigma Hydrids are much faster.
4. Count for at least an hour, as rates are modest.
5. Use the same nights for the Monocerotids and early Geminids.