Solar Eclipse 20 March 2015

January 15, 2015 Leave a comment

On the morning of Friday 20 March 2015 there will be a total eclipse of the Sun. Between 0830 and 1042 the Moon will pass across the face of the Sun, blocking out part of its light. The maximum extend of the eclipse will happen at 0934 for a few minutes.

A Total Eclipse of the Sun, visible from the Faroe Islands on 20 March 2015

A Total Eclipse of the Sun, visible from the Faroe Islands on 20 March 2015

Unfortunately the “path of totality”, i.e. those parts of the world that will see a total eclipse, is in the far north Atlantic and Arctic oceans. Residents of the Faroe Islands get a ring-side seat at the total eclipse.

Path of Totality, Friday 20 March 2015

Path of Totality, Friday 20 March 2015

That said, it will still be a dramatic event in the UK, south of the path of totality, as we will see a partial solar eclipse where the Moon blocks some but not all of the Sun’s light.

A partial eclipse from Anamosa, Iowa. Credit: Steve Wendl - See more at: http://astrobob.areavoices.com/page/112/#sthash.ElDDdLAg.dpuf

A partial eclipse from Anamosa, Iowa. Credit: Steve Wendl – See more at: http://astrobob.areavoices.com/page/112/#sthash.ElDDdLAg.dpuf

The further north you are in the country the more of the Sun will be obscured, but wherever you are in the UK it’ll look quite dramatic. Here’s a handy table showing what % of the Sun’s disk will be obscured by the Moon from where you are.

Town/City % Eclipse on 20 March 2015
Lerwick, Shetland 96.8%
Kirkwall, Orkney 96.6%
Inverness 95.6%
Aberdeen 93.9%
Glasgow 93.7%
Edinburgh 93.1%
Belfast 93.0%
Newcastle 90.7%
Liverpool 89.4%
Manchester 89.1%
Birmingham 87.3%
Cardiff 86.7%
London 84.4%

Compare this with the August 1999 eclipse, where totality passed across the SW of England. During that eclipse the further south you were in the UK the better. Indeed the SW of England and the Channel Islands saw a total eclipse.  I was in Glasgow and saw an 82% eclipse. For me, this eclipse will be even better. In fact for anyone north of Liverpool, the 2015 eclipse is better than that in 1999!

Town/City % Eclipse on 11 August 1999
Lerwick, Shetland 67.9%
Kirkwall, Orkney 68.7%
Inverness 76.8%
Aberdeen 77.6%
Glasgow 82.2%
Edinburgh 81.8%
Belfast 86.8%
Newcastle 84.8%
Liverpool 90.5%
Manchester 90.1%
Birmingham 93.5%
Cardiff 97.2%
London 96.6%

Wherever you are in the UK though it’s worth watching, but BE CAREFUL. Never look at the Sun directly, even when it’s eclipsed. Here are some safety guidelines for viewing eclipses.

Stargazing Hotel Breaks And Cruises 2015

December 20, 2014 3 comments

In 2015 I’m delighted to be hosting a range of stargazing events, from stargazing weekend breaks under some of the UK’s darkest skies, to a cruise to one of the most remote islands in the world, steeped in astronomy history.

Steve Owens’ contribution was perfect. We liked how he joined in with the guests at meals etc and held the group together. He has a gift of being able to convey his knowledge in terms easy to understand.His lecture with slides was really informative and interesting as was the enthusiasm he put into answering our every question or listening to our accounts of minor brushes with stars!!

Here’s a list of the hotels I run stargazing breaks at:

Glenapp Castle, Ballantrae, Scotland (Galloway Forest Dark Sky Park)
Kirroughtree House Hotel, Newton Stewart, Scotland (Galloway Forest Dark Sky Park)
Selkirk Arms Hotel, Kirkcudbright, Scotland (Galloway Forest Dark Sky Park)
Yarn Market Hotel, Dunster, Exmoor (Exmoor Dark Sky Reserve)

And here’s the cruise I’m hosting:

Stargazing and astronomy cruise, 4-22 May 2015, Cape Town to St Helena. On this stargazing tour you will have the opportunity to stargaze from a truly unique place – St Helena. The island is steeped in astronomical history, and you’ll visit the sites of Halley’s observatory (he of comet fame), as well as those of the other astronomers who have visited St Helena over the centuries. Its location near the equator means that virtually every constellation in the sky is visible at one time or another from St Helena, and visitors from the UK will be amazed to see a whole new collection of stars in the southern hemisphere that simply aren’t visible from Europe: the famous Southern Cross, the Magellanic Clouds, and the galactic centre of the Milky Way.

Here’s a list of the weekends I’m running throughout the year. Click the links for the hotels above to find out more or to book!

Stargazing weekend break, 20-22 February 2015, at the Yarn Market Hotel, Dunster, in Exmoor International Dark Sky Reserve

Stargazing weekend break, 13-15 March 2015, at the Selkirk Arms Hotel, Kirkcudbright, near Galloway Forest Dark Sky Park

Stargazing weekend break and Solar Eclipse Special, 20-22 March 2015, Kirkcudbright, near Galloway Forest Dark Sky Park (this weekend break can be extended to a three night stay to watch the partial eclipse of the sun at sunrise on Friday 20 March!)

Stargazing weekend break, 9-11 October 2015, at the Selkirk Arms Hotel, Kirkcudbright, near Galloway Forest Dark Sky Park

Stargazing weekend break, 4-6 December 2015, at Kirroughtree House Hotel, Newton Stewart, in Galloway Forest Dark Sky Park

Stargazing weekend break, 11-13 December 2015, at Kirroughtree House Hotel, Newton Stewart, in Galloway Forest Dark Sky Park

 

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!

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

Autumn Equinox 2014

September 23, 2014 Leave a comment

Today, 23 September 2014, marks the moment of the Autumn Equinox. At 0229 UT (0329 BST) the Sun will cross from the northern hemisphere sky to the southern, and we’ll begin the slow approach to the Winter Solstice on 21 December.

The equinoxes (one in spring and one in autumn) are the two instances every year when the Sun makes that crossing from north to south and vice versa, and they’re commonly thought to be the days when day and night are equal length, but they’re really not, for reasons I’ve outline before:

  • Astronomers measure the timings of equinoxes, sunrises and sunsets based on the middle point of the Sun’s disk in the sky, so when you read a sunrise time it means the time that the centre of the Sun’s disk rises above the horizon. For a few minutes before that time the top of the Sun’s disk will already have risen, giving “daylight”.
  • Even before this happens the sky is lit up by the Sun below the horizon, and we experience twilight. Most people would think that the sky is bright enough to call it “daytime” long before the Sun pops above the horizon, during the phase of civil twilight.
  • So today, even though day and night are said to be equal on the equinox, the “daytime” (i.e the start of civil twilight) started about 0625BST in Glasgow (where I am) and will end this evening around 1950BST, giving me approx. 13.5 hours of “daylight”. (Londoners will have from about 0615 until 1930BST, or approx. 13.25 hours of “daylight”).

The day this year where I have exactly 12 hours of “daylight” (i.e. between the morning start and the evening end of civil twilight) is 11 October and this day is called the equilux. (In London the equilux falls on 12 October).

Join me for IndyRef Stargazing on Twitter!

September 16, 2014 3 comments

Join me this Thursday night / Friday morning (18/19 September 2014) for some Twitter-based stargazing!

Coll night sky, some of the darkest skies in Europe

Coll night sky, some of the darkest skies in Europe

Many people will be staying up late or even overnight to watch the results of the Scottish Independence Referendum come in. To while away the wee small hours I thought it’d be fun to do a bit of stargazing too!

If you find yourself staying up late then join in by following me on Twitter @darkskyman, and using the hashtag #indyrefstargazing. I’ll kick things off around 9pm on Thursday as the sky darkens, and throughout the night I’ll be describing what’s up in the sky, and how best to see it, winding up around 6am as the dawn breaks. By then we’ll be eagerly awaiting the result of the referendum, which is estimated to be around 7am.

Join in, it’ll be fun! You can send me questions via Twitter too, or just say hello. You don’t need any equipment to take part: just your eyes and clear skies. If you’ve got binoculars, dig them out, as you’ll be amazed how much more you can see.

Northern Lights Alert 12/13 September 2014

September 12, 2014 2 comments

*** UPDATE 0630UT 13 September: Overnight, some UK aurora watchers caught sight of some northern lights. Reports from Northumberland, N Norfolk, and those parts of Scotland not shrouded in fog. Now it’s night time in N America, activity rates have dropped off but it’s worth keeping an eye on Spaceweather.com for the Kp index to get back up to storm level (5+), as well as the NOAA Spaceweather Now page for the Bz component to turn S. Both of these have to happen in order for a good aurora display.***

Stargazers in the northern UK should look out for northern lights tonight and tomorrow, Friday 12 and Saturday 13 September 2014.

Aurora over Aberdeenshire, by Mark Tait @marktait78, taken 27 February 2014

Aurora over Aberdeenshire, by Mark Tait @marktait78, taken 27 February 2014

Two large solar eruptions blasted material off the Sun on 9 and 10 September, and that material has been hurtling through space for the last couple of days. The first batch of it hit our atmosphere in the small hours of this morning, resulting in some moderate northern lights displays seen from North America. The second batch has arrived this afternoon, and could possibly trigger a dramatic display of northern lights overnight and tomorrow night.

If you’ve never seen the northern lights (aurora borealis) before then this is an ideal opportunity to catch them. It’s unlikely that this display will be as good as the once-in-20-year display we saw back in February this year, but you never know. It’s hard to predict these things until they actually happen.

If you want to see the northern lights there are a few things you can do to increase your chances:

1. Find an observing site with a clear northern horizon
2. Get away from light pollution; put towns and cities behind you to the south (i.e. head to the northern edge of your town or city, preferably further)
3. Be patient. Aurorae can be faint and indistinct at first, and you need to let your eyes dark adapt to see them properly

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