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Perseids Meteor Shower 2016

August sees the return of the most reliable meteor shower of the year; the Perseids, with rates of shooting stars possibly increasing to over 100 per hour under perfect conditions.

Read my previous blog post Meteor Showers: The What, How, Where, When, Why for general advice on how best to observe meteor showers.

A shooting star – otherwise known as a meteor – is a tiny piece of space dust that burns up in our atmosphere, forming a bright, brief streak of light in the sky. Many people have never seen a shooting star, and think they’re rare events, but given dark skies you can expect to see a few every hour on a clear night. From cities, under light polluted skies, you can’t see most of the faint ones, and so only the rarer bright ones are visible.

However at regular times each year the Earth moves through thick clouds of space dust – left behind by comets – and we get a dramatically increased rate of meteors. On the night of 12/13 August we’ll pass through the densest part of a dust cloud left behind by Comet 109P/Swift-Tuttle, and will see the rate of meteors increase by a factor of 20!

You can begin watching for Perseid meteors now, and the shower will last until late-August, but the peak of the shower occurs overnight on 12/13 August 2016, which means that the nights on either side of this will be best for meteorwatching.

Location of the Perseids Radiant at 0001 on 13 August

Location of the Perseids Radiant at 0001 on 13 August

The best time of night to watch the meteor shower is from around 2200 onwards on 12 August, once the radiant, the point from where the meteors appear to originate, rises above the horizon. However the moon will be in the sky until after midnight, and will interfere slightly for observers in dark sites. The later you observe the higher the radiant will be, and the more meteors you’ll see.

The number of meteors that you will observe every hour depends on a number of factors:
•the density of the dust cloud 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 darkness of your sky, measured using naked-eye limiting magnitude, a measure of the faintest object you can see.

This year the Perseid meteor shower has an expected zenith hourly rate (ZHR) of around 150. 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 that perfect. In the UK, for example, the radiant of the shower will not be at the zenith; it will be around 30° above the horizon at 2200, 40° high at midnight, and 50° high at 0200.

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 Persieds 2016.

ZHR = 150 at the peak, say.

h = 30° at 2200, 40° at 0000, 50° at 0200, 65° at 0400

k = 0 (let’s hope!)

m = 6.5 (if you’re observing under skies free from light pollution)

So your actual hourly rate under clear dark skies is

(150 x sin(30))/((1/(1-0) x 2^(6.5-6.5) = 75 meteors per hour at 2200
(150 x sin(40))/((1/(1-0) x 2^(6.5-6.5) = 96 meteors per hour at 0000
(150 x sin(50))/((1/(1-0) x 2^(6.5-6.5) = 115 meteors per hour at 0200
(150 x sin(65))/((1/(1-0) x 2^(6.5-6.5) = 135 meteors per hour at 0400

Remember though that these numbers apply only to the peak of the Perseid occuring at these times. If the peak happens at 0400 on 13 August (and we’re not sure exactly when it’ll occur) then you might see 135 meteors per hour, but “only” 75 per hour if the peak occurs at 2200 on 12 August.

Remember that these rates are for perfectly dark skies. If you live in suburbia then divide these numbers by 4 or 5; if you live in a bright city divide these numbers by 10. Take home message: get somewhere dark!

It is worthwhile having a look on the days leading up to the peak, when the numbers of meteors will be gradually increasing towards this rate.

Live in or near Glasgow? Come and join me for the Perseids #Meteorwatch at Whitelee Wind Farm!

Perseids Meteor Shower 2015

August 5, 2015 2 comments

This month sees the return of the most reliable meteor shower of the year; the Perseids. And with a New Moon occuring at the same time as the peak of this shower this is the perfect opportunity to see hundreds of shooting stars.

Read my previous blog post: Meteor Showers: The What, How, Where, When, Why for general advice on how best to observe meteor showers.

A shooting star – otherwise known as a meteor – is a tiny piece of space dust that burns up in our atmosphere, forming a bright, brief streak of light in the sky. Many people have never seen a shooting star, and think they’re rare events, but given clear dark skies you can expect to see a few every hour on a clear night. From cities, under light polluted skies, you can’t see most of the faint ones, and so only the rarer bright ones are visible.

However at regular times each year the Earth moves through thick clouds of space dust – left behind by comets – and we get a dramatically increased rate of meteors. We’re already within the diffuse outer reaches of the dust cloud that forms the Perseids, and on the night of 12/13 August we’ll be in the densest part of that cloud, and will see the rate increase by a factor of 20!

You can begin watching for Perseid meteors now, and the shower will last until late-August, but the peak of the shower occurs overnight on 12/13 August 2015, which means that the nights on either side of this will be best for meteorwatching.

Location of the Perseids Radiant at 0001 on 13 August

Location of the Perseids Radiant at 0001 on 13 August

The best time of night to watch the meteor shower is from around 2200 onwards on 12 August 2014, once the radiant, the point from where the meteors appear to originate, rises above the horizon. The later you observe the higher the radiant will be, and the more meteors you’ll see.

The number of meteors that you will observe every hour depends on a number of factors:
•the density of the dust cloud 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 darkness of your sky, measured using naked-eye limiting magnitude, a measure of the faintest object you can see.

The Perseid meteor shower has a zenith hourly rate (ZHR) of around 100. 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 that perfect. In the UK, for example, the radiant of the shower will not be at the zenith; it will be around 30° above the horizon at 2200, 40° high at midnight, and 50° high at 0200.

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 Persieds 2015.

ZHR = 100 at the peak, say.

h = 30° at 2200, 40° at 0000, 50° at 0200, 65° at 0400

k = 0 (let’s hope!)

m = 6.5 (if you’re observing under skies free from light pollution)

So your actual hourly rate under clear dark skies is

(100 x sin(30))/((1/(1-0) x 2^(6.5-6.5) = 50 meteors per hour at 2200
(100 x sin(40))/((1/(1-0) x 2^(6.5-6.5) = 64 meteors per hour at 0000
(100 x sin(50))/((1/(1-0) x 2^(6.5-6.5) = 77 meteors per hour at 0200
(100 x sin(65))/((1/(1-0) x 2^(6.5-6.5) = 90 meteors per hour at 0400

Remember though that these numbers apply only to the peak of the Perseid occuring at these times. If the peak happens at 0400 on 13 August (and we’re not sure exactly when it’ll occur) then you might see 90 meteors per hour, but “only” 20-25 per hour if the peak occurs at 2200 on 12 August.

Remember that these rates are for perfectly dark skies. If you live in surbribia then divide these numbers by 4 or 5; if you live in a bright city divide these numbers by 10. Take home message: get somewhere dark!

It is worthwhile having a look on the days leading up to the peak, when the numbers of meteors will be gradually increasing towards this rate.

After the Peak: How Long Does a Meteor Shower Last?

August 13, 2014 Leave a comment

I had a question on Twitter asking whether it was worth while looking out for any Perseid meteors tonight after the shower peaked yesterday.

While individual meteors are short blink-and-you’ll-miss-them events, meteor showers themselves last many days, sometimes weeks. The rate of meteor activity builds up in the days before the peak, and tails off afterwards. The peak itself lasts a few hours, maybe a day or so for some broad-peaked showers.

Take a look at this graph of activity for the Perseids meteor shower 2013:

Perseids 2013 Rate (from imo.net)

Perseids 2013 Rate (from IMO.net)

The number of meteors per hour under ideal conditions (known as the ZHR, the Zenith Hourly Rate) built up to around 20 meteors//hour during the month before the peak. The rate started to increase around 9 Aug, doubling to 40 meteors//hour around 11 Aug, before tripling again to 120 meteors//hour around 13 Aug at the peak. The drop off was quicker, but even for the two days after the peak the rate was still above 20 meteors//hour.

So even in the days after the peak of the Perseids rates of meteors stat well above the background rate, at least 4 or 5 times that for a couple of nights.

My Perseids Meteorwatch

August 9, 2013 3 comments

On Monday night one of the year’s most spectacular meteor showers is set to peak.

You’ll get a great view of it if you’re somewhere dark with clear skies. But those of us stuck in the city can see plenty too.

I’ll be heading to the grounds of Glasgow Science Centre to view it, and you’re welcome to join me. A few things first:

If it’s cloudy or raining DON’T COME! I won’t be there.

I’ll be there from around 10pm, probably till around midnight.

If you want a great view then head somewhere dark, but if you’re in Glasgow and don’t want to head out of the city this is a decent site.

This ISN’T a formal event; I’ll be hanging out there and you’re welcome to come under your own steam. You’ll be responsible for your own safety and comfort; bring extra clothing, a torch, and a deck chair if you have one.

You can park in Glasgow Science Centre car park for £3. Public transport at that time of night is pretty sparse.

Glasgow Science Centre will NOT be open, so there’s no access to refreshments or toilets etc.

Thanks to Glasgow Science Centre for letting us use their outside space.

Perseids 2013: The What, How, Where, When, and Why

Here’s a simple guide for observing the Perseids 2013 meteor shower this year, covering five basic questions:
What is the Perseids meteor shower?

The Perseids meteor shower is the most reliable of the active regular meteor showers that happen throughout the year. A meteor shower is a display of meteors (or shooting stars) where you see lots of them in the space of just a few hours. The Perseids occurs around the same time each year, in mid-August, and during the peak of the shower meteor rates increase from just a few an hour (the background rate that you’ll see on any clear, dark night) up to maybe 100 or 200 meteors every hour for observers in the perfect location. Meteorwatchers in the UK will probably see dozens per hour from dark sites, dropping to a few an hour (still worth watching for) in towns and cities.

How can I observe the meteor shower?

You don’t need any special equipment to observe a meteor shower; just your eyes. Try and get as far from city lights as possible (out into the countryside if you can, or into a local park if not), and get comfortable. You might want to bring a reclining deck chair with you, as that makes meteorwatching much more civilised! Just lie back and take in as much of the sky as possible. If you’re lucky enough to see a good display of meteors, you might see as many as one a minute, maybe more!

Where should I look?

Meteors streak across the whole sky, so you don’t need to look in any specific direction, but of course if you’ve got a tall building or tree that’s blocking the view, or a streetlight nearby that’s a bit glare-y, then put these to your back. The Perseids meteors all appear to streak from a point in the sky (called the radiant) in the constellation of Perseus (hence the name) which rises in the east about 10pm local time, climbing to its highest in the sky towards dawn.

When is it happening?

The peak of the meteor shower will probably happen some time around 1815 and 2045 UT (1915 and 2145 BST) on Monday 12 August 2013, although there are uncertainties here. The peak could happen any time between 1415 BST 12 Aug and 0215BST 13 Aug. This means that observers in the UK might catch the peak of the shower, if it happens after the sky darkens on 12 August. Even on the nights on either side we’ll still see plenty. In fact the peak of the Perseids is several days wide, so you can start meteorwatching early, and carry on well after 12 August, so that even if this weekend is cloudy you’ll almost certainly have a chance to see some Perseids. Whatever night you’re out you’ll see more the later you’re up. Starting after dusk, the meteor rate will increase each night as Perseus climbs higher in the sky towards dawn.

Why do meteor showers happen?

Meteors are tiny bits of space dust streaking through our atmosphere. These motes of dust float about in space and as the Earth orbits the Sun it hoovers them up. Sometimes the Earth passes through a particularly dense clump of dust, and we get lots of meteors, in a meteor shower. These clumps of dust are left behind by comets as the orbit the Sun, their streaking tails leaving behind a trail of tiny rock particles. The comet that left behind the space-rocks that we’ll see in the Perseids meteor shower is called Swift-Tuttle, after the two astronomers that discovered it in 1862.

Perseids Meteor Shower 2012

August 7, 2012 1 comment

UPDATE: Here’s my easy guide to the what, how, where, when and why of the Perseid Meteor Shower.

This month sees the most reliable meteor shower of the year; the Perseids. You can begin watching for Perseid meteors now, and the shower will last until late-August, but the peak of the shower occurs around mid-day on Sunday 12 August 2012, which means that the nights on either side of this will be good for meteorwatching.

Perseus at 0200 Monday 13 August 2012

The best time of night to watch the meteor shower is from around 2200 onwards on both 11 and 12 August 2012, once the radiant, the point from where the meteors appear to originate, rises above the horizon.

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 Perseid meteor shower has a zenith hourly rate (ZHR) of between 50 and 200. 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 that perfect. In the UK, for example, the radiant of the shower will not be at the zenith; it will be around 30° above the horizon at midnight, and 45° above the eastern horizon at 2am.

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 Persieds 2012.

ZHR = 100 at 1200 on Sunday 12 August 2012, but by 0001 on Monday 13 August, ZHR might be down to 50 say, maybe less.

h = 30° at 0001, 45° at 0200, 60° at 0400

k = 0 (let’s hope!)

m = 6.5 (assuming you can get somewhere dark).

So your actual hourly rate at 0200 under clear dark skies is

(50 x sin(30))/((1/(1-0) x 2^(6.5-6.5) = 25 meteors per hour at 0001 Monday 13 August
(50 x sin(45))/((1/(1-0) x 2^(6.5-6.5) = 35 meteors per hour at 0200 Monday 13 August
(50 x sin(60))/((1/(1-0) x 2^(6.5-6.5) = 45 meteors per hour at 0400 Monday 13 August

Remember though that these numbers might be lower if the ZHR drops off after the daytime peak.

It is of course worthwhile having a look on the days leading up to the peak, when the numbers of meteors will be gradually increasing towards this rate.

You can keep track of the increasing ZHR at the International Meteor Organisation website.

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

Perseids: Last Chance to See?

August 9, 2011 Leave a comment

Tonight (9/10 August 2011), between Moonset and the start of twilight, might present the best opportunity to view the Perseids meteor shower, at around 0200, although the peak of the shower doesn’t occur until the night of 12/13 August 2011.

The International Meteor Organisation has been recording the increasing ZHR (activity level) of this year’s Perseids meteor shower, and it currently stands at ZHR=20. It is expected to increase over the next four nights to ZHR=50-200 at the peak on 12/13 August.

IMO's ZHR for Perseids 2011

However, tonight is the last night of the shower where the Moon will be absent from the sky for part of the night, setting before 0200. After the Moon sets there will be a period of time before twilight begins where the sky will be free of any natural light pollution, so assuming you can get away from man-made light pollution you’ll maximise your chances of seeing meteors.

How long you will have under dark skies will depend on where in the UK you are, with observers in the far south of England having until 0330, while those in southern Scotland having until 0230. Observers north of central Scotland will not experience truly dark skies for several days yet. (To find your local Moonset and twilight times visit timeanddate.com)

If you can get somewhere very far from light pollution (like Galloway Forest Dark Sky Park, or Exmoor National Park) then you’ll have the best chance of seeing lots of meteors tonight. Let’s take these locations as demonstrations of how the actual hourly rate will vary between tonight and the peak at the weekend.

Observing Night Hours of true darkness
(Glentrool)
Hours of true darkness
(Exmoor)
Limiting Mag
(due to Moon)
ZHR (estimate) Actual Hourly Rate
 09/10 August  0148-0225  0207-0322  6.5  25  22
 10/11 August  none (due to Moon)  none (due to Moon)  4.5  30  7
 11/12 August  none (due to Moon)  none (due to Moon)  4.0  35  5
 12/13 August  none (due to Moon)  none (due to Moon)  3.5 (Full Moon)  100 (peak)  11* (peak)

*The peak ZHR has been taken here to be 100, although it may be as much as twice this, meaning that even under a Full Moon you’ll see the same at the peak as you will under dark skies tonight.

So if you can get somewhere truly dark tonight between Moonset and the start of astronomical twilight (and you might get less than an hour of these perfect conditions) then your Actual Hourly Rate tonight may be better than that during the peak, due to the Full Moon then.

For those observing in towns and cities this won’t be such a big issue, as man-made light pollution will impose a limiting mag on the sky tonight, which will reduce tonight’s Actual Hourly Rate rate to ~3, compared to ~11 at the peak.

So if you get the chance head out tonight, and indeed every night this week, to look for Perseids in the wee small hours. This is the most reliable shower of the year, and one that even the Full Moon cannot ruin completely!

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