Tue, 14 Nov 2017
Will there be a Leonid meteor storm?
Old engraving of a meteor storm
A Leonid storm in 2017? Simple answer: No. Longer answer: probably not.
The Leonid meteors, visible each year in November, have in the past produced the most spectacular displays of shooting stars ever recorded. In 1833 and 1866, and again in 1966, literally thousands of meteors poured out of the sky to produce a true meteor storm. Reports claimed that there was no part of the sky that was not filled with shooting stars.
These displays are caused by a swarm of dust particles along the track of Comet Tempel–Tuttle, which orbits the Sun once every 33¼ years. The swarm lags behind the comet itself, and the Earth encounters the densest part in years when the comet itself is close to the Sun. By chance, these occur in years 33, 66 and 99 in each century, which makes the maths easier.
But this year, the comet is just about as far as it can get from Earth, beyond the orbit of Uranus. So don’t worry about a collision! Nor will the comet be anywhere near us in 2032 when it is next close to the Sun.
And because the comet is at the other end of its orbit, the particles that have spread along its orbit will also not be very plentiful. However, there will still be a few shooting stars to be seen, so if it’s clear it will be worth keeping a watch for them this weekend, though numbers visible are only likely to be a few per hour, even at peak time, which is on the early morning of Saturday, 18 November.
The official rate expected is up to 15 an hour, but bear in mind that this only applies under ideal conditions, and includes the more numerous faint meteors which are not visible in typical UK skies. The good thing is that in 2017 the Moon will be new, so it won’t interfere with observing at all.
And there's just a tiny chance that there may be a denser clump of material that could produce higher numbers, but even if there were it would only be for a very short time. Those fantastic displays of the past were also limited to a matter of hours, and many parts of the world didn't see anything like those numbers. So if you read somewhere that 'astronomers say there could be a dramatic display of shooting stars tonight', take it with as many pinches of salt as they claim there will be meteors!
The orbit of Comet Tempel–Tuttle. Graphics from JPL
When and where to watch
Start watching any time after around 10.30 pm, and continue as long as you can, because rates are likely to rise throughout the night. Look anywhere in the sky apart from the east, which is where the meteors will appear to stream from. That way, you’re more likely to notice them. They are very fast, so each one will be over in literally a flash.
You don’t need to be anywhere special in the UK (or indeed the world) to see them, but try and get away from city lights and make sure you can see as much of the sky as possible.
Although the peak rates are due on the night of Friday–Saturday, 17–18 November, there could be Leonid meteors on nights either side. And you could also see meteors which are not Leonids. There are also likely to be just as many random meteors occurring as Leonids: these are known as sporadic meteors, and they can occur at any time. You can tell a Leonid because it will appear to come from the direction of the constellation of Leo, which rises in the east north east around 11 pm, whereas sporadics can come from any part of the sky. There are also Taurid meteors, which emanate from Taurus, in the south.
Position of the Leonid radiant, which moves night by night
As a quick guide, look for the well-known constellation of Ursa Major, better known as the Plough or Big Dipper. Follow its two right-hand stars downwards and they point to the source of the meteors (known as the radiant). These two stars also point upwards to the Pole Star, but the Leonid radiant is about the same distance in the other direction.
Q & A
Will Comet Tempel-Tuttle hit Earth in future?
Although its orbit intersects that of Earth, the comet is always well clear of this point in November when the Earth crosses its path. The closest it gets to Earth for the next few centuries will be in December 2163, but it will be well above the plane of the Earth’s orbit. Even then, the comet will be some 20 million km from Earth.
What causes a shooting star?
This happens when a tiny grain of dust from a comet hits Earth’s upper atmosphere. The speed of impact from the Leonids is about 71 km/sec so in no time they heat up and vaporise, leaving a trail of ionised air that is visible from the ground. This all happens at altitudes of around 100 km above Earth’s surface. It’s amazing that such a tiny particle can be visible at such a distance.
Why are the Leonids so fast?
Comet Tempel-Tuttle orbits the Sun in the opposite direction to Earth, so the closing velocity of the dust particles is greatly increased. Some other meteor showers, such as the Taurids, which are active at the same time as the Leonids, are much slower because the bodies orbit in the same direction around the Sun as the Earth.
Is there any danger from the Leonids?
Yes – you might catch a chill if you don’t dress up warmly! But there’s no risk of the shooting stars reaching the ground – they all disintegrate high in the atmosphere.
How can I photograph the meteors?
They happen so quickly that as soon as you spot one, it’s gone – so there’s no time to swing the camera round and press the shutter. The only way is to keep the shutter open for as long as you can and hope that one dashes through the field of view during the exposure.
|A Leonid meteor photographed by David Entwistle|
- Put the camera on a tripod or fix it viewing the sky
- Use a high ISO setting –- 1600 or higher
- Make sure the camera is focused on infinity. Switch off auto-focus, as the camera will have nothing to focus on
- Give the longest exposure you can without the image being overexposed due to light pollution. Compact cameras may not allow more than a few seconds’ exposure, but aim for at least 30 seconds if possible, with the lens at full aperture
- Check for dewing up every so often
- Aim at about 45º altitude (halfway up the sky) and a similar distance from the radiant.
Added by: Robin Scagell