Geminid meteor shower at a glance
| Detail | Value |
|---|---|
| Activity window | about December 4 to December 20 |
| Peak | around December 14 |
| Zenithal hourly rate (ZHR) | about 150 |
| Radiant | Gemini, near the star Castor |
| Parent body | asteroid 3200 Phaethon |
| Entry speed | about 35 km/s |
These values follow the International Meteor Organization (IMO) calendar. For all showers in one list, see the meteor shower calendar.
A shower from an asteroid
Most meteor showers come from comets. The Geminids are unusual because their parent is 3200 Phaethon, an object discovered in 1983 that looks like an asteroid. Phaethon orbits the Sun about every 1.4 years and comes very close to the Sun, closer than Mercury. Scientists still debate exactly how it produced so much debris. One idea is that intense heating near the Sun cracks its surface and releases dust. Another is that it shed material in a more active past.
Because Geminid particles are thought to be denser than the fluffy dust of most comets, they survive a little longer in the atmosphere and often look bright and steady.
What to expect
A ZHR of about 150 is the rate an observer would see under perfect conditions with the radiant overhead. In practice, from a dark rural site at mid-northern latitudes, more than 100 meteors an hour around the peak is possible on a clear, moonless night. From a suburban site you may see a few dozen an hour, still a fine show.
Geminids move at about 35 km per second, which is medium speed. They often appear as graceful, fairly long streaks rather than quick flashes, which makes them easy to enjoy.
Where and when to look
The radiant is close to Castor, one of the two bright stars that mark the heads of the twins in Gemini. In December, Gemini rises in the northeast in the early evening and is high overhead around 2 AM local time. That means:
- You can start watching around 9 or 10 PM.
- Rates usually climb until the radiant is highest, after midnight.
- The shower is visible from the Southern Hemisphere too, though the radiant is lower and rates are smaller.
Look at a dark part of the sky, roughly 45 degrees from the radiant. Meteors appear in all directions.
Moonlight
The richness of the Geminids means they hold up better than most showers under moonlight, but a bright Moon still hides the fainter meteors. Check the moon phases for mid-December and the moonrise and moonset times for your location. If the Moon sets late in the night, the evening hours may be darker, or the other way round.
Viewing tips
- Dress for winter. December nights in the Northern Hemisphere are cold. Wear layers, a hat and gloves.
- Bring a reclining chair or insulated mat. You will see more sky with less strain.
- Avoid lights and screens. Allow 20 to 30 minutes for your eyes to adapt fully.
- Watch the night of December 13–14. It usually gives the best rates, but the nights before are good too.
- Try photography. A camera on a tripod with a wide-angle lens and long exposures can capture bright Geminids.
- Stay a while. Meteors come in clusters and quiet spells; an hour or more gives the best experience.
The Ursids follow a week later. For other events in the sky, see the sky tonight.