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Geminids Meteor Shower 2015

December 11, 2015 1 comment

One of the most active and reliable meteor showers, the Geminids, happens every year in mid-December. This year’s display promises to be a good one for those meteorwatchers with clear skies.

The maximum rate of Geminids is predicted to occur around 1800 on 14 Dec 2015, but peak rates normally persist for around a day, so the nights of 13 and 14 Dec are both good for meteorwatching. In addition. you’ll see plenty of Geminids from now until a few days after the peak.

When Gemini Sends Stars to Paranal  Image Credit & Copyright: Stéphane Guisard (Los Cielos de America), TWAN

When Gemini Sends Stars to Paranal
Image Credit & Copyright: Stéphane Guisard (Los Cielos de America), TWAN

There are a few ways you can maximise your chances of seeing some Geminids (see The What, How, Where, When and Why) but the best way is to get somewhere dark, like one of the UK’s International Dark Sky Places. I’ll be heading down to Galloway Forest in SW Scotland.

The Geminids’ radiant (the point in the sky where all the meteors appear to emerge from) rises at sunset, so you can begin your meteorwatch as soon as it gets dark enough. The Moon is only 3 days old at maximum so you’ll have no interference to your dark skies.

The number of meteors that you will observe every hour depends on a number of factors:

  • the density of the cloud of dust that the Earth is moving through, that is causing the shower in the first place;
  • the height above the horizon of the radiant of the shower, the point from which the meteors appear to radiate;
  • the fraction of your sky that is obscured by cloud;
  • the naked-eye limiting magnitude of the sky, that is a measure of the faintest object you can see.

The Geminids meteor shower has a maximum zenith hourly rate (ZHR) of  around 120 (the highest of any meteor shower). This is the number of meteors that you can expect to see if the radiant is directly overhead (the point in the sky called the zenith), and you are observing under a cloudless sky with no trace of light pollution.

However conditions are rarely perfect. In the UK, for example, the radiant of the shower will not be at the zenith; it will be around 10° above the horizon at 1800h, 25° above the horizon at 2000h, 40° at 2200h, 60° at 0000h, and at its highest of 70° at 0200h.

Assuming a clear night, the other factor is the limiting magnitude of the sky, a measure of the faintest object you can see. Man-made light pollution will be an issue for most people. From suburbia the limiting magnitude of the sky is ~4.5 (around 500 stars visible), so you will only be able to see meteors that are at least this bright; the fainter ones wouldn’t be visible through the orange glow. In a big city centre your limiting magnitude might be ~3 (only around 50 stars visible); in a very dark site like Galloway Forest Dark Sky Park the limiting magnitude is ~6.5 (many thousands of stars visible), limited only by the sensitivity of your eye. So in most cases it’s best to try and get somewhere nice and dark, away from man-made light pollution.

The calculation that you need to make in order to determine your actual hourly rate is:

Actual Hourly Rate = (ZHR x sin(h))/((1/(1-k)) x 2^(6.5-m)) where

h = the height of the radiant above the horizon

k = fraction of the sky covered in cloud

m = limiting magnitude

Let’s plug the numbers in for the Geminids 2015.

ZHR = 120 (maximum)

h = 10° at 1800, 25° at 2000, 40° at 2200, 60° at 0000, 70° at 0200h

k = 0 (let’s hope!)

m = 6.5 (if you get somewhere really dark!)

So your actual hourly rate under clear dark skies is

(120 x sin(10))/((1/(1-0) x 2^(6.5-6.5) = 21 meteors per hour at 1800
(120 x sin(25))/((1/(1-0) x 2^(6.5-6.5) = 50 meteors per hour at 2000
(120 x sin(40))/((1/(1-0) x 2^(6.5-6.5) = 77 meteors per hour at 2200
(120 x sin(60))/((1/(1-0) x 2^(6.5-6.5) = 104 meteors per hour at 0000
(120 x sin(70))/((1/(1-0) x 2^(6.5-6.5) = 112 meteors per hour at 0000

If you’re observing in suburbia you need to divide these numbers by around 4, and in bright cities by 10! Nonetheless, even in a city if you’re out at midnight during peak activity you’ll see around 10 meteors per hour.

Remember though that these numbers are assuming perfectly clear skies under perfectly dark conditions, and are assuming a peak rate of 120 at each of these times. It probably won’t be quite this good, but the bottom line is: there’s never a better night to see meteors!

Orionids Meteor Shower 2014

October 9, 2014 Leave a comment

October sees a fine meteor shower, the Orionids, grace our skies. While not reaching the maximum rates of one of the Big Three Meteor Showers (Perseids, Geminids, and Quadrantids), this month’s shower is still impressive, coinciding as it does this year with the new moon, meaning dark skies and lots of meteors for those who can get out of towns and cities.

Orionids Meteor Shower

Orionids

See: Meteor Showers: The What, How, Where, When, Why 

All meteor showers happen as the Earth passes through a cloud of dust left behind by comets (or in rare cases asteroids). The Orionids is associated with the most famous of all comets, Halley’s Comet, which orbits the Sun every 75.3 years.

The best time of night to watch the Orionids meteor shower is from local midnight onwards, once the radiant (the point from where the meteors appear to originate) rises well above the horizon. The maximum rate for this shower is due to occur on 21 October 2014, but unlike the big three meteor showers the Orionids peak is very broad, lasting several days rather than several hours, and so it’s worth watching on any night for a few days either side of the peak.

The ZHR of the Orionids during 2012, from imo.net

The ZHR of the Orionids 2012, from imo.net

Compare this chart with that for the Perseids meteor shower peak, which is much narrower (although because the Perseids is a much more active shower the ZHR stays high – above 20 – for roughly the same amount of time!):

Perseids 2013 Rate, from imo.net

The ZHR of the Perseids 2013, from imo.net

The number of meteors that you will observe every hour depends on a number of factors:

  • the density of the cloud of dust that the Earth is moving through, that is causing the shower in the first place;
  • the height above the horizon of the radiant of the shower, the point from which the meteors appear to radiate;
  • the fraction of your sky that is obscured by cloud;
  • the naked-eye limiting magnitude of the sky, that is a measure of the faintest object you can see.

The Orionids meteor shower has a maximum zenith hourly rate (ZHR) of  around 25 (sometimes the ZHR can be higher, up to 40, sometimes even 70, but that isn’t expected this year). This is the number of meteors that you can expect to see if the radiant is directly overhead (the point in the sky called the zenith), and you are observing under a cloudless sky with no trace of light pollution.

However conditions are rarely perfect. In the UK, for example, the radiant of the shower will not be at the zenith; it will be around 15° above the horizon at midnight, 30° above the horizon at 2am, 45° at 4am, and reaching a maximum height of 50° due south before dawn

Assuming a clear night, the other factor is the limiting magnitude of the sky, a measure of the faintest object you can see. Man-made light pollution will be an issue for most people. From suburbia the limiting magnitude of the sky is ~4.5 (around 500 stars visible), so you will only be able to see meteors that are at least this bright; the fainter ones wouldn’t be visible through the orange glow. In a big city centre your limiting magnitude might be ~3 (only around 50 stars visible); in a very dark site like Galloway Forest Dark Sky Park the limiting magnitude is ~6.5 (many thousands of stars visible), limited only by the sensitivity of your eye. So in most cases it’s best to try and get somewhere nice and dark, away from man-made light pollution.

The calculation that you need to make in order to determine your actual hourly rate is:

Actual Hourly Rate = (ZHR x sin(h))/((1/(1-k)) x 2^(6.5-m)) where

h = the height of the radiant above the horizon

k = fraction of the sky covered in cloud

m = limiting magnitude

Let’s plug the numbers in for the Orionids 2014.

ZHR = 25 (maximum)

h = 15° at 0001, 30° at 0200, 45° at 0400

k = 0 (let’s hope!)

m = 6.5 (if you get somewhere really dark!)

So your actual hourly rate under clear dark skies is

(25 x sin(15))/((1/(1-0) x 2^(6.5-6.5) = 6.5 meteors per hour at 0001
(25 x sin(30))/((1/(1-0) x 2^(6.5-6.5) = 12.5 meteors per hour at 0200
(25 x sin(40))/((1/(1-0) x 2^(6.5-6.5) = 17.7 meteors per hour at 0400

If you’re observing in suburbia you need to divide these numbers by around 4, and in bright cities by 10!

Remember though that unlike other meteor showers where the peak lasts only a few hours these rates for the Orionids can last days, so any time you’re outside at night it’s worth looking up!

*UT = Universal Time = GMT, so for UK times (BST) add one hour to these

A New Meteor Shower for 2014: The Camelopardalids

January 9, 2014 Leave a comment

UPDATE: See below

This year sees a brand new meteor shower possibly gracing our night skies, on 24 May 2014.

Meteor showers occur when the Earth passes through a cloud of dust left behind by a comet. These clouds hang in space in the same place, and so meteor showers occur at the same time every year as the Earth revisits them.

But every so often a new comet comes along and creates a cloud of dust where none existed before. In the case of this anticipated shower the comet that left the cloud behind goes by the name of 209P/Linear. It was discovered in 2004 and passed near the sun in 2009, and will do so again this year in early May.

Current predictions are that the Earth will pass through the cloud of dust left by 209P/Linear on 24 May 2014. Quite how many shooting stars will be visible is unknown, but given that this is a fresh cloud of dust that hasn’t been “used up” before in previous meteor showers, we might expect a good display.

Stargazers in North America are probably best suited to see it, but in the UK it’s still worth looking out for. More accurate information regarding timings will become available nearer the time, but regardless of when exactly the Earth passes through the dust stargazers in the UK will have to wait until the sky is dark. It never gets truly dark in the UK in late May except in the south, and the Channel Islands, but the best time is between 0000 and 0200.

And where to look in the sky? As with all meteor showers it doesn’t matter where you look; the shooting stars streak across the sky in all directions. However if you trace the trails back they will all converge at the same part of the sky, called the radiant. Meteor showers are named after their radiants (e.g. the Perseids emerge from Perseus, and the Geminids from Gemini) and this new shower will appear to emanate from the dim constellation of Camelopardalis*, so they’ll be known as the Camelopardalids! Just flows off the tongue…

* Camelopard comes from the romanised Greek words for “camel” and “leopard”, and is the name for a giraffe, which the Greeks thought were part camel, part leopard!

UPDATE: The International Meteor Organisation repeats the need for caution in predicting how good this meteor shower might be:

[M]uch is unknown about this comet, including its dust productivity and even its precise orbit. Consequently, while tentative proposals have been made that ZHRs at best could reach 100+, perhaps up to storm proportions… these are far from certain. The strongest activity could be short lived too, lasting perhaps between a few minutes to a fraction of an hour only. In addition, the number of dust trails involved means there may be more than one peak, and that others could happen outside the “key hour” period, so observers at suitable locations are urged to be vigilant for as long as possible to either side of the predicted event to record whatever takes place. Remember, there are no guarantees in meteor astronomy!

They suggest that independent calculations show that the peak of activity (which might be very narrow, see above) will fall some time around 0700-0740UT (0800-0840BST) Saturday 24 May which obviously means that UK observers will miss the peak (US meteorwatchers will be perfectly placed).

However it is still worthwhile keeping an eye out during the darkest part of the night on the nights of 23/24 and 24/25 May in case there are multiple peaks, or the main peak is broad.

We just don’t know yet what is going to happen with this meteor shower: it might fizzle out to nothing, or it might reach storm levels, meaning hundreds of shooting stars per hour. Good luck!

Leonids Meteor Shower 2012

November 15, 2012 3 comments

One of the year’s regular meteor showers, the Leonids, happens this weekend, peaking at around 0930 on 17 November 2012. It (usually*) isn’t one of the very active showers (such as the Perseids, Geminids or Quadrantids), with the maximum rate in a normal year between 10-20 meteors per hour in perfect conditions.

The peak of the Leonids is quite broad, lasting several days, so between now and early next week it’s worth looking up to see if you can catch a glimpse of any shooting stars. The best time to view the Leonids shower is in the pre-dawn hours, but any time after 11pm on Thursday through to Tuesday night should mean you’ll see at least a few meteors.

How to see the Leonids Meteor Shower

1. Find somewhere dark with as little light pollution as possible. The countryside is best, but if you’re stuck in a city try and get away from as many lights as possible.
2. Bring a reclining deck chair. Standing outside looking up for long stretches of time gets uncomfortable.
3. Bring a blanket. It gets VERY cold outside at night in November.
4. Position yourself under your blanket on your reclining deck chair so that you take in as much of the sky as possible. Although the meteors all appear to radiate out of the constellation of Leo in the SE there’s no need to specifically face this direction as the meteors will streak across any part of the sky.
5. Wait. The rate of this shower isn’t very high, so you might only see one every five or ten minutes, maybe less often than that, so patience is a virtue.

* every 33 years the Leonids meteor shower turns into a meteor storm, in which the rates dramatically increase by a factor or 50 or more, up to perhaps several thousand meteors per hour. This regularity is due to the nature of the origin of the dust that causes these meteors. It comes from the tail of a comet, Comet Temple-Tuttle, which orbits the Sun once every 33 years. This means that the dust trail left behind by the comet – and subsequently hoovered up by the Earth to make a meteor shower at the same time every year – is refreshed every 33 years, resulting in a spike of activity for a few years afterward each pass of the comet. The comet last renewed the trail in 1998, and so the years 1999, 2001 and 2002 were all spectacular years for the Leonids, with storm rates peaking at 3000 Leonids per hour. I was lucky enough to see all of these showers, the most memorable being 2002 where in the space of just two hours under half-cloudy skies on the outskirts of Glasgow I saw over 300 shooting stars.

Quadrantids Meteor Shower 2012

January 2, 2012 Leave a comment

On the night of 03/04 January 2012 the first meteor shower of the year will take place, the Quadrantids. This shower ranks as one of the best performers of the year, assuming your skies aren’t clouded, as they so often are in winter. If the peak of this shower occurs under ideal conditions – i.e. perfectly clear skies, free from light pollution – then you can expect to see in excess of 100 meteors every hour. The peak for this shower is very brief though, so you’ll have to catch just the right conditions at just the right time to see a display this good. This year’s peak is estimated to occur just before dawn on 04 January 2012.

Not only do you have the weather to contend with, but this year the waxing gibbous Moon will be up for much of the night. However the Moon sets at around 0415, giving you a couple of hours before the sky starts to brighten before sunrise. Given that the peak of this shower will probably occur within this short window, things are looking pretty good for this year’s display.

Last year’s graph of meteor activity shows how sharp the peak is, so you probably won’t see many Quadrantids on the nights either side of the peak, but it’s worth a look if you have clear dark skies. ZHR for this year may be anywhere between 60 and 200.

Quadrantids Activity from 2011, credit imo.net

How best to view the Quadrantids 2012

  1. Get somewhere as far from street lights and city glow as possible, preferably somewhere really dark, like your nearest national park or one of the UK’s dark sky places: Galloway Forest Park, Sark or Exmoor.
  2. Go out at the right time, which for this year’s shower is between around 0400 and 0700 GMT.
  3. You don’t need binoculars or a telescope, your eyes are best for viewing meteors.
  4. Wrap up warm, as if you have clear skies (which you’ll be hoping for) it will be very cold in these early morning hours.
  5. Bring a reclining deck chair so you don’t have to stand all night, and a blanket to wrap yourself in!
  6. Although the radiant of the meteor shower (the point where the meteors will appear to stream from) is high in the E around 0400 you don’t need to worry about facing in any particular direction, just position yourself so that you can see as much sky as possible, and enjoy the view!

You can follow the progress of the meteor shower at meteorwatch.org, or on twitter via @VirtualAstro and the #meteorwatch hashtag.

If you want to make more serious observations of this shower you can submit them to either the International Meteor Organisation, the British Astronomical Association, or the Society for Popular Astronomy.

Leonids Meteor Shower 2011

November 10, 2011 1 comment

On the night of 17/18 November 2011 the Leonids meteor shower reaches its peak. This annual performer is associated with Comet Temple-Tuttle, which orbits the Sun once every 33 years leaving a trail of debris as it goes. Once a year the Earth passes through this trail, and we see a meteor shower.

Leonids 2001

This year’s Leonids shower is hampered by the last quarter Moon which sits just to the right of the radiant of the Leonids, in Leo. Despite this there is good reason to observe the shower this year, as the International Meteor Organisation suggest there might be as many as three peaks of activity.

Throughout November the rate of Leonids will increase, with the main peak occurring at 0340 GMT on 18 November, at which time the Zenith Hourly Rate may be 20+. For observers in the UK, observing under cloudless skies, away from light pollution, this translates as an hourly rate of ~14, but the Moon will interfere and reduce this value somewhat. Two other peaks may also occur, at ~2100 on November 17, and at ~2300 on 18 November, with similar rates. This means that both the nights of 17/18 and 18/19 November may offer good opportunites to observe this shower.

The Leonids has the distinction of being the most dramatic meteor shower that I’ve ever seen, as I observed the Leonid meteor storms every year from 1998 to 2002, when we saw hundreds of meteors each night at the peak of the shower. These storm peaks are predictable, and occur every 33 years, associated with the pass of comet Temple Tuttle, as it refreshes the trail of debris that cause the meteors. The next pass of Temple Tuttle is due 2031, so we’ve a long wait for the next storm.

Interestingly, the Leonid storm of 1833 was truly stunning, with rates estimated to be around 100,000 per hour across North America.

To view the Leonids, find a dark spot, away from light pollution, sit on a reclining deck chair facing as large an area of the sky as you can manage, wrap yourself in a blanket, and enjoy the view. For observers in the UK the meteor shower radiant will rise around 2200 GMT on 17 November and will be high in the SE by 0400 on 18 November.

If you want to make observations of the Leonids that might help scientists better understand the shower, you can do so via the Society of Popular Astronomy, or the British Astronomical Association. Lots more info can be found at the Meteorwatch website.

Meteor Showers & the Zenith Hourly Rate

May 6, 2010 1 comment

Today (6th May 2010) was the maximum of a meteor shower called the eta-Aquarids. This shower lasts many weeks, beginning on 19th April and ending around 28th May, with a peak of activity today. If you look up info for this shower you will find quoted a Zenith Hourly Rate (ZHR) of 85.

That means  if you were oberving this shower in perfect conditions – no light pollution, no cloud, no moon, and with the radiant of the shower (the point where the meteors appear to emerge from) directly overhead (at the zenith) you would expect to see around 85 shooting stars per hour.

It won't look like this

When people talk about meteor showers they sometimes quote the ZHR as an indication of how many you can expect to see, but this is often misleading, for reasons I’m about to discuss.

Let’s use the eta-Aquarids shower as an example.

If I wanted to view the shower at it’s most advantageous position I’d need to go out around 0200 tomorrow morning, after the radiant had risen in the east, and before the sky starts to brighten as we enter twilight.

The radiant at this point will be very low, about 5° above the horizon, well short of the 90° it needs to be for the radiant to appear directly overhead.

This isn’t the only problem; the Moon is up in last quarter phase, rising before the radiant, and so the Moon’s light will drown out the fainter meteors.

Then there’s light pollution. From my garden I can see stars (and meteors) down to around magnitude 4, and so the fainter ones won’t be visible through the orange city glow. Let’s assume the Moon’s glow won’t be any worse than the man-made light pollution.

And finally there’s the more mundane problem of cloud cover. If my sky isn’t entirely clear of clouds, then I may miss some of the shooting stars.

How do these factors effect the number of meteors I’ll see? We can put them into an equation to find out:

Actual Hourly Rate = =(ZHR x sin(h))/((1/(1-k)) x 2^(6.5-m)) where

h = the height of the radiant above the horizon

k = fraction of the sky covered in cloud

m = limiting magnitude

Tonight for the eta-Aquarids at 0200 ZHR = 85, h = 5°, m = 4 (optimistically), k = 0 (very optimistically)

Therefore the actual hourly rate of eta-Aquarids I can expect is

(85 x sin(5))/((1/(1-0)) x 2^(6.5-4)) = 1.3, or just over one per hour. Not great at all, and that’s assuming a cloudless sky!

But don’t let that put you off. You never know, if you pop out at 0200 (perhaps taking a break from the UK election coverage) look over to the east and maybe you’ll catch that one bright eta-Aquarid meteor…

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