The Geminids come around again

Here is a space-picture of how the meteors of this stream cross Earth’s orbit.

Geminid meteors in space

The picture shows the courses of several particles with slightly different orbital elements, to suggest the vastness of the stream in space. Earth’s collecting of a relative few of them is like a bullet passing through a cloud of gnats. We show the Sun 10 times larger than it really is, Earth 500 times, so even the line representing Earth’s course is thicker than the real Earth.

Properly, the particles are “meteoroids” when they are hurtlint through outer space; they become “meteors” if and when they hit our atmosphere and vaporize with flashes of light, or “meteorites” in the even rarer chance that they survive to be found as lumps somewhere on Earth.

They are bits of dust or rock that separated from the asteroid 3200 Phaethon, so they still approximately follow its orbit. The diagram shows their courses over a span of 120 days, centered on their perihelia (nearest points to the Sun). Red indicates the parts of the orbits south of the ecliptic plane. Those passing us now will pass closest to the Sun in July.  Shortly after that, they return northward through the ecliptic plane, then fly on out, to return about 20 months later.

They approach us from outside and north of our orbit. It is the angle between these approaching paths and our own December path that causes them to appear to radiate from the direction that we call the constellation Gemini.

Geminid radiant rising

Hers is the Geminid radiant appearing above the northeastern horizon early in the night. The meteor trails shown are of course schematic; they can be in any part of the sky (tending to appear longer in more distant parts), but you know they are Geminids if you can trace them back to near the Twin stars. The hazy band of light is the Milky Way; the imaginary “Earth’s shadow” is at the point opposite to the Sun.

The Geminid shower is nowadays perhaps the year’s most reliably abundant; you could see 50 an hour, or more, during its most intense hours. It is convenient also (for people in Earth’s north hemisphere) because the radiant is in the sky for the whole of this long near-midwinter night. True, it is liable, like most meteor showers, to be best in the after-midnight hours: the radiant keeps climbing higher (parallel to the “motion of the sky” arrow on the celestial equator) until about 2 AM. If you are up and out about that time, you are facing into the Geminid stream, and you are around on the front side of your planet as it curves along its course around its star.


4 thoughts on “The Geminids come around again”

  1. Here in NE England, the abysmal weather’s been primarily the apparently endless gales since early November, but there’s been plenty of clouds and rain too. However, I did catch a glimpse of Geminid activity on Dec 12/13, but just for about thirty-five minutes after 23:30 UT, as the day’s clouds broke up only around 23h, and returned soon after midnight, if then without the day’s rain at least. Seven Geminids and four sporadics seen in a limiting magnitude +5.6 sky in that time, so pretty healthy activity under less than ideal conditions, and largely what I’d have expected about 24 hours ahead of the maximum, with rising Geminid rates.

    Sadly, Dec 13/14 was disappointing, with heavy overcast, yet more rain, mist then fog after midnight till beyond dawn. Hazily clear at times through the day since, with a very watery Sun, but back to overcast, mist and fog tonight (14/15) so far.

    Checking various places online hasn’t found a whole lot more, with the radio and radar meteor observers among the only real successes so far, but the NASA all-sky fireball camera results posted on the webpage give further hints as to what’s been happening. They recorded 107 of 148 fireballs as Geminids on Dec 14, for example, up from 15 out of 29 on Dec 13 and just 6 of 21 on Dec 12. Of course, the actual fireball numbers are affected night to night by weather conditions, so the percentage of Geminids per night is a more useful value, at 72, 52 and 29% on the three respective nights.

  2. Clouded out here too in NY :( Should have looked the night before peak when less cloudy, maybe not as many , but might have been some worth reporting. Better luck next time.

  3. Great weblog. Thanks for the update.

    It’ll be mostly cloudy in northern Ohio, 6/8 to 7/8 cloud cover, but that sometimes means the clouds range from 5/8 to 8/8 of the sky. At the low end, 3/8 of the sky is visible, meaning 20 meteors per hour, or one very 3 minutes.

    That’s worth seeing, if I get my Christmas shopping done.

    I’m sure you know about the KP Index. I keep an eye on it at

    1. Thanks, Rick. It’s been almost solid cloud for most of the past month in southern Britain. It looks like being much the same in Portugal, where I shall be till nearly the end of the year. There is a low to the west of Britain, with bands of cloud revolving around it counterclockwise over Europe.

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