Archive

Posts Tagged ‘geminids’

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!

Geminids Meteor Shower 2014

December 8, 2014 2 comments

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 between sunset on 13 Dec and sunset on 14 Dec, so the night of 13 Dec is the best bet, although nights on either side will still show plenty of shooting stars.

UPDATE: The excellent International Meteor Organisation (imo.net) have issued a live graph of Geminid activity. Last night the peak rate was around 46/hr +/- 21/hr. That rate will only increase overnight tonight, to a peak of around 120/hr.

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. You’ll have until near midnight under dark skies, at which point the last quarter moon will rise to brighten the sky a little and drown out some of the fainter meteors.

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 just as the Moon rises to spoil the view a little.

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 2014.

ZHR = 120 (maximum)

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

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

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.

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 nearly this good, but the bottom line is: there’s never a better night to see meteors!

Geminids Meteor Shower 2011

December 11, 2011 Leave a comment

The best view of the Geminids Meteor Shower this year will be after midnight on the nights of 13/14 and 14/15 December, however the hourly rate of meteors will be drastically reduced due to the presence of a waning gibbous Moon which will be high in the sky at the peak meteor times, and right next to the part of the sky that the Geminid meteors will appear to radiate from (called the radiant).

A Geminid Meteor (image credit Wally Pacholka / AstroPics.com / TWAN)

The light from the Moon will drown out all but the brightest meteors, and so rather than seeing 80+ meteors per hour (under cloudless skies, free of light pollution) that rate may be reduced to only a few an hour. This still represents an increase in the normal background rate of meteors, but is far from the spectacular display usually seen during this reliable performer.

To maximise your chances of seeing meteors you should plan to spend a few hours outside after midnight. A reclining lawn chair is ideal, allowing you to observe in comfort, and wrapping yourself in blankets should stave off much of the midwinter chill.

You should face your lawn chair away from the Moon, so you are not in its direct glare. Although the radiant of the shower will be behind you if you do this, the meteors will streak all over the sky, and so there is no real harm in facing away.

More information about the Geminids meteor shower can be found at the Meteorwatch website.

Geminids 2010 Meteorwatch Podcast

January 26, 2011 Leave a comment

Galloway Forest Park’s recreation ranger Lucy Hadley has put together a great podcast from recordings she took during the Geminids Meteorwatch event we ran in the Dark Sky Park on 13 December 2010.

You can listen to it here

On the podcast you’ll hear me, Dr Martin Henrdy from the Astronomy Dept of Glasgow University, and Dr Marek Kukula, public astronomer at the Royal Observatory Greenwich, as we lead the group of meteorwatchers in a tour of the sky. Mainly what you’ll hear though are whoops and squeals of delight as the crowd sees meteor after meteor streaking overhead. A great night!

Meteor Showers for 2011-2012: Ones to watch

January 4, 2011 8 comments

With the Quadrantids meteor shower that has just past yielding around 100 meteors per hour in near-perfect New Moon conditions, which showers of the next two years will give us as good a display?

Meteor Shower

There are a few regular, dependable showers that can be relied on to put on a good show year after year, given a good Moon phases, so let’s concentrate on those:

Lyrids 2011
The Lyrids peak this year on April 21/22, only three days after the Full Moon, making conditions far from ideal. The ZHR is around 20, but under bright Moon conditions this will be much reduced, so that from the UK you might only see a few Lyrids per hour.

Persieds 2011
The Perseids peak on 12/13 August 2011 coincides exactly with a Full Moon, making this shower pretty much a write-off in 2011.

Orionids 2011
The Orionids peak occurs on 21/22 October 2011 just after the last quarter Moon, with the Moon rising a little after midnight, just as the meteor shower radiant is gaining height. Again, far from ideal.

Leonids 2011
The Leonids peak on 17/18 November occurs during a last quarter Moon, which unfortunately is smack bang in the direction of Leo, and so will obscure many of the Leonids in 2011

Geminids 2011
The Geminids peak on 13/14 December 2011 will likewise be completely obscured by an almost-full Moon in Gemini.

Quadrantids 2012
The Quadrantids peak on 3/4 January 2012 will feature a waxing gibbous Moon which won’t set until 0400.

Lyrids 2012
The Lyrids peak on 21/22 April 2012 is the first major shower peak in 15 months where the Moon is absent, meaning that you should get good views of this shower which has a ZHR of only around 20.

Persieds 2012
The Perseids peak of 12/13 August 2012 will feature a thin waning crescent moon that’s visible in the sky from midnight, obscuring some of the Perseids. Here’s my up-to-date guide to the Perseids 2012.

Orionids 2012
The Orionids peak on 21/22 October 2012 is pretty much Moon-free from around 2330, as the Moon sets.

Leonids 2012
The Leonids peak on 17/18 November 2012 will also be Moon free from early evening, and so presents an opportunity to see a few Leonids.

Geminids 2012
Rounding off this two year run of poor Moon conditions for meteor showers, we end with the Geminids on 13/14 December, coinciding wonderfully with a New Moon on 13 December, meaning conditions will be near perfect.

The Geminids 2010: Status Update

December 14, 2010 Leave a comment

I spent last night helping run a great meteorwatch event in Galloway Forest Dark Sky Park, on the evening of the peak of the Geminids Meteor Shower. According to the International Meteor Organisation;

The Geminids is one of the finest, and probably the most reliable, annual meteor shower. Activity exceeds 100 meteors per hour around December 14, with meteors radiating from a point near Castor in constellation Gemini. Geminids are slow, bright and occasionally colorful. Many observers consider the shower to be more spectacular than the famous Perseids in August, but the Geminids are less widely known because of the cold and often clouded December nights in the northern hemisphere.

The latest report from the IMO is that the Zenith Hourly Rate (a measure of the shower’s activity) got up to around 80 meteors per hour at midnight last night, with it due to increase to around 120 at the actual peak at 1100 this morning. This rate will drop off over the next few days, but it’s still worth looking out for some tonight (14 Dec).

We had great clear skies in Galloway Forest Dark Sky Park, but the temperature was as low as -6°C. Despite the cold, dozens of people turned up to Glen Trool Village Hall to hear Dr Marek Kukula, Public Astronomer at the Royal Observatory Greenwich, deliver an excellent talk on “Collisions, Craters and Impacts”.

After the talk, at 9pm, we drove in convoy a short distance up the road to a large rally car park, where we spent several hours stargazing and meteorwatching. We were joined by Dr Martin Hendry from the University of Glasgow, and Keith Muir of the Forestry Commission Scotland, and the four of us led the gathered stargazers on a guided tour of the night sky, punctuated by cries of “ooh” and “aah” as meteors streaked overhead.

Galloway Forest Park’s recreation ranger, Lucy Hadley was also on hand recording snippets of interview for her podcast, which will be available in a few days time (watch this space).

The International Meteor Organisation (IMO) was founded in 1988 and has more than 250 members now. IMO was created in response to an ever growing need for international cooperation of meteor amateur work. The collection of meteor observations by several methods from all around the world ensures the comprehensive study of meteor showers and their relation to comets and interplanetary dust.

Geminids Meteor Shower 2010: What You Might See

November 23, 2010 1 comment

The final meteor shower of 2010 is the Geminids, the peak of which falls on the night of the 13/14 December 2010. The Geminids is described by the IMO as “one of the finest, and probably the most reliable, of the major annual showers presently observable”, and this year’s shower is set to put on a good show. (You can read the IMO’s rather technical summary of the 2010 Geminids here: http://www.imo.net/calendar/2010#gem)

It won't look like this

The predicted Zenith Hourly Rate (see my previous post about ZHR and what it actually means here) is around 120. Although the peak is predicted to occur around 1100 on 14 December, it should happen some time between 1840 on 13 December and 1600 on 14 December 2010. The best time for the peak to occur for stargazers in the UK would be between 0030 and 0600 on 14 December, after the Moon sets but before twilight begins.

The radiant for this shower is actually quite favourable, and if you wait till the Moon sets at around 0030 on 14 December then the only light pollution limiting your view will be man-made. If you observe before the Moon sets then you will lose a few of the fainter Geminids in its glow, but it’s only a first quarter moon, and so will only really have an impact if you’re observing from very dark skies.

Let’s use the equation relating ZHR to actual observations of meteors to work out how many you might see:

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

In the case of the 2010 Geminids, if observed from the UK, h = 45 degrees. Let’s assume you have clear skies (haha) with k = 0.

The number of Geminids you can expect to see from a variety of observing sites is as follows:

For very light polluted sites, such as city centres m = 3, and therefore you can expect to see only around 8 meteors per hour.

In suburban skies near a city or town centre m = 4, and you’ll see around 15 meteors per hour.

In rural skies where m = 5, you’ll see 30 meteors per hour.

Under very dark skies, where m = 6.5 (i.e. where there is no or negligible effect of light pollution, like in Galloway Forest Dark Sky Park) you’ll see up to 85 meteors per hour, once the Moon sets. A first quarter moon will impose a limiting magnitude, even at a very dark site, of around 6, in which case you’ll see a slightly reduced 60 meteors per hour.

Remember, all of these numbers assume perfectly clear skies. If half your sky is cloudy, cut these numbers in half!

How many Geminid meteors will I see?

Where are you observing from? Limiting magnitude Number of Geminids per hour
Very light polluted city centre 3 7 or 8
Suburban Site 4 15
Rural Site 5 30
Dark Sky Site 6.5 85 (after the Moon sets at 0030)

If you fancy a good view of this spectacular meteor shower, then head to Galloway Forest Dark Sky Park, where we have an evening of talks and meteorwatching planned, weather permitting!

%d bloggers like this: