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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

Perseids Meteor Shower 2014

August 10, 2014 Leave a comment

This month sees the most reliable meteor shower of the year; the Perseids. However this year the near-full Moon will be in the sky too, brightening the sky so much that only the brightest Perseid meteors will be visible. It’s still worth looking up over the next week if you have clear skies, in case you might spot a bright Perseid.

You can begin watching for Perseid meteors now, and the shower will last until late-August, but the peak of the shower occurs on Tuesday 12 August 2014, which means that the nights on either side of this will be best for meteorwatching, albeit with interference from the moon.

Perseus at 0200 13 August 2014

The best time of night to watch the meteor shower is from around 2200 onwards on both 11 and 12 August 2014, 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.

This year though the full Moon is a great leveller, giving everyone a limiting magnitude of around 3.

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 2014.

ZHR = 100 at the peak, say.

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

k = 0 (let’s hope!)

m = 3 (pesky moon!)

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

(100 x sin(30))/((1/(1-0) x 2^(6.5-3) = 4.4 meteors per hour at 0001
(100 x sin(45))/((1/(1-0) x 2^(6.5-3) = 6.2 meteors per hour at 0200
(100 x sin(60))/((1/(1-0) x 2^(6.5-6.5) = 7.6 meteors per hour at 0400

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

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

Mercury at maximum elongation, 25 May 2014

May 13, 2014 1 comment

The planet Mercury is the most elusive of all of the naked eye planets. It orbits nearest the Sun, and so always rises just before the Sun or sets just after it, appearing in the glow of twilight. For much of Mercury’s orbit it isn’t visible at all, lying too close to the Sun in the sky.

To see Mercury at its best you have to wait until it’s as far as possible from the Sun in the sky; what astronomers refer to as its maximum elongation. When Mercury is at its maximum eastern elongation it’s visible just before sunrise; when it’s at its maximum western elongation its visible just after sunset.

At the moment Mercury is nearing its maximum western elongation and so makes a perfect evening target.

Mercury in the WNW, at Maximum Elongation, 25 May 2014

Mercury in the WNW, at Maximum Elongation, 25 May 2014, created using Stellarium

Mercury’s range of maximum elongation is between 18° and 28°, and in this particular apparition it’s furthest distance from the Sun is 22.7°. This occurs on 25 May 2014. Between now and the end of May look west just after sunset to try and catch a glimpse of Mercury shining at magnitude +0.4. It’ll be low in the sky, very low, but if you look towards the west, find Jupiter shining brilliantly, and follow a line down to the right at an angle of approx. 45° you should see Mercury a few degrees above the horizon.

If you’re trying to observe it through a telescope then make sure you wait until the Sun has well and truly set below the horizon. Mercury exhibits phases like the Moon and Venus which can be seen through a telescope but shows no other detail through an earth-based scope; on 25 May the disk of Mercury facing the Earth will only be 40% illuminated, making a fat crescent shape. Mercury’s angular size is the smallest of all the planets save distant Uranus and Neptune.

If you’ve ever seen Jupiter or Saturn through a telescope then you’ll know that they look spectacular despite their relatively meagre size. On 25 May, for example, Jupiter will appear to have a diameter of 33 arcseconds (written 33″), Saturn 19″, Venus 15″, Mars 12″, and Mercury a paltry 8″.

And you can actually see all five of these planets on the night of 25 May (or any night between now and the end of May. Mercury is the trickiest to find, but Jupiter will be blazing low in the east, Mars high in the south, Saturn lower in the south-east, and if you’re keen to get up before sunrise you’ll see Venus low in the east. (Uranus and Neptune are dawn objects too at the moment).

Lyrids Meteor Shower 2014

April 16, 2014 3 comments

UPDATE: the peak of this year’s Lyrids is expected at 1700 UT on 22 April, so for UK meteorwatchers the best time is pre-dawn on 22 April or after midnight on 23 April. Via @popastro

Starting tonight and peaking next week on 22/23 April 2014 is our spring season’s best meteor shower, the Lyrids. It’s not nearly as dramatic as the Big Three meteor showers – the Perseids in mid-August, the Geminids in mid-December, and the Quadrantids in early January –  but dedicated meteorwatchers will catch glimpses of plenty of shooting stars overnight around or after midnight on 21/22 or 22/23 April.

Meteors

Meteors

The peak rate (more correctly the Zenith Hourly Rate) of the Lyrids is around 20 meteors per hour, but that’s under ideal conditions: 100% clear skies, zero light pollution, and the radiant (the point at which the meteors appear to emerge from) at the zenith (directly overhead). In the nights leading up to the peak you can still expect to see a few but the ZHR is much lower, around 5 meteors per hour.

So how many Lyrids can we expect to see from the UK next week at the peak? To work this out we’ll have to make some assumptions, and then crunch some numbers.

Let’s assume clear skies at least. Then we’ll assume that the peak will fall either some time between dusk on 21 April and dawn on 22 April or some time between dusk on 22 April and dawn on 23 April (currently the suggestion is that it’ll be pre-dawn on 22 April, but it’s worth watching out on both nights). Finally we’ll assume that the ZHR at the peak will be around 20.

The only limiting factors then are (a) the height of the radiant above the horizon, which changes as Lyra rises in the east, climbing high in the south by dawn; and (b) the light pollution

Time Height of Radiant* Hourly rate if peak occurs at this time
2200 21 or 22 April 18° 6
2300 21 or 22 April 25° 8
0000 21 or 22 April 32° 11
0100 22 or 23 April 40° 13
0200 22 or 23 April 49° 15
0300 22 or 23 April 57° 17
0400 22 or 23 April 65° 18**
0500 23 April 71° 19**

* This is based on my observing location in Glasgow, but it’ll only be a few degrees out .
** The last quarter Moon rises around 0330 and so will create enough light pollution to significantly reduce these numbers.

Location Limiting Magnitude Divide above hourly rates by…
Bright Urban 3.5 8
Urban 4 6
Bright Suburban 4.5 4
Suburban 5 3
Rural 6 1.5
Truly Dark 6.5 1

These graphs of previous years show the how the Lyrids activity rate increases and decreases with time centred round a peak on 22 or 23 April:

Lyrids Activity 2011

Lyrids Activity 2011

lyr2012overview

Lyrids Activity 2012

lyr2013overview

Lyrids Activity 2013

Mars at Opposition 2014

This week the red planet Mars reached opposition, making it best placed for observing. Opposition is, as the name suggests, the point where a planet is directly opposite the Sun in our sky.

This means that Mars is up all night long at the moment, rising as the Sun sets and setting as the Sun rises, and so you should be able to spot it whatever time of night you’re out.

Mars reached opposition on 8 April, but on 14 April it will reach its closest approach to Earth, at a mere 57.4 million miles!

On that night – and on nights near that date – the planet Mars will shine very brightly at magnitude -1.5, brighter than anything else in the night sky except the Moon (which is Full on 14 April, and sits near Mars) and Jupiter.

Mars in the sky at midnight on 9 April

Mars in the sky at midnight on 9 April

Mars also looms larger than normal when seen through a telescope, at a whopping 15″ (15 arcseconds = 0.25 arcminutes = 1/240 of a degree!). Stargazers with a decent sized telescope, good observing skills, and good observing conditions should be able to make out the north polar cap of Mars which is tilted towards us at the moment.

Through a small scope you might catch it looking like this:

Mars as seen through a small telescope

Mars as seen through a small telescope

The Great Northern Lights Display of 27 Feb 2014

February 28, 2014 1 comment

Last night, Thursday 27 February 2014, the UK was treated to one of the best displays of Northern Lights in the past twenty years. Twitter erupted with excitement, and then pictures, which my good friend @VirtualAstro and myself @darkskyman RT-ed and commented on throughout the evening.

Aurora over Aberdeenshire, by Mark Tait @marktait78

Aurora over Aberdeenshire, by Mark Tait @marktait78

Below is just a sample of some of the best images that came in last night, but before that let’s look at why this aurora display was so good.

Two days previously a large sunspot on the surface of the Sun erupted with a huge X-class flare, rated at X4.9, the strongest of the year so far. This flare blasted off material from the Sun’s surface in what’s known as a Coronal Mass Ejection (CME). We knew that this material wasn’t aimed straight at us, but last night, two days after the eruption, it sideswiped the Earth, getting caught in our magnetic field and funnelled to the north and south poles.

It just so happened that the angle of the impact, and the timing, was perfect for evening skywatchers across the UK, and with largely clear skies across the country reports started coming in around 7pm that we might be about to see storm level activity. In the end it was rated as G2 (moderate) but the position of the auroral oval meant that even this moderate storm produced some of the best views of aurorae in the UK that I can remember.

Don’t be downhearted if you missed it; there’s a chance (55% according to NOAA) that we might see more tonight as we move through the wake of the CME. It’s unlikely to be as good as last night’s show, but still worth a look.

I tweeted the best way to see the aurora:

Then images started coming in!

This from @garethpaxton in Central Scotland (a pic of the viewfinder of his camera):

Then this beautiful one from Jim Hunter Images in East Lothian:

From @ross1772 in Newmill, Scotland

Dave @makapala uploaded a bunch of images taken from Fife to his Flickr account:

Mark Tait @marktait78 got this amazing image from Aberdeenshire, showing the verticality of the aurora:

England also got some of the action with the aurora stretching as far south as Uttoxeter, in this image by @RichardH082:

And Whitby (from @whitbyglenn)

From Ravenscar (from @andy_exton)

And NE England (via @Astro_Matt27)

Northern Ireland got in on the action too, as this amazing image from Paul Martin shows:

But of course the best of it was in the north of Scotland, such as this stunning image from Innes Mackay in Lewis:

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!

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