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Credit: David Dickinsen

2012 is here, and the world shows no sign of ending as the heavens spin on their appointed rounds high overhead. But the diligent observer may be rewarded with several unique an spurious sights, both natural and manmade…

1^st up is everyone’s favorite meteor shower named after an obsolete constellation; the Quadrantids peak the morning of January 4^th in what is the first large meteor shower of the year. The peak is very swift, only lasting about 12 hours or so and is centered this year on 2:00 AM EST/7:00 AM UTC. This favors the U.S. East Coast in 2012, as the 79% waxing gibbous Moon will set around 2AM local the morning of the 4^th for observers in mid-northern latitudes. The radiant of the shower lies at a declination of 52° degrees north at the junction of the modern constellations of Draco, Bootes and Hercules, and thus activity may be visible pre-midnite local, although the setting of the Moon and the rising of the radiant will raise sighting prospects considerably. Expect swift-moving meteors headed outward from the radiant above the handle of the Big Dipper to appear anywhere in the sky. The Quadrantids have been known since the early 1800’s, but there has been much conjecture as to the source parent body. Astronomer Fred Whipple noted in 1963 that the stream bears some resemblance to the Delta Aquarids, and that the orbital path has undergone alterations by the planet Jupiter in the last few thousand years. In 2003, SETI researcher Peter Jenniskens proposed that the source may be then recently discovered asteroid 2003 EH1, which has been tentatively linked to Comet C/1490 Y1, which approached Earth at a distance of 0.52 Astronomical Units on January 12^th 1491. Be sure to keep an eye out for Quadrantids on these chilly January mornings, as we commemorate Quadrans Muralis, a constellation that is no longer! Read the rest of this entry »

I am the dead albatross on your boat.

I am the peacock feather in the house.

I am horseshoe carelessly nailed upside down so all the good luck falls out down a grid.

If you ever see me coming to stand next to you at a star party, meteor shower, or eclipse, you have permission to make the cross sign with your fingers and run backwards as fast as you can.

That’s because, for my 33 and a half years of sky gazing, I have managed to cause cloudy skies and inclement weather at every single major event I have attended.

Just for the record, I’m a keen amateur astronomer without a telescope. I follow as many Twitter astro accounts as I can, avidly retweeting the latest data from Cassini, and following lonely Mars landers as they bump across rusty rocks. I cried the first time I saw the ISS, and as a child, I used to stand in the garden with a compass, straining hard to see the northern lights. I never did.

My bad luck began in earnest when I went to Cornwall for the eclipse. A boyfriend and I spent a small fortune hiring out a dank, uncomfortable cottage in the middle of nowhere. I was so excited that I woke up at 6.30am every morning, causing us to be grey faced and exhausted for the whole pitiful ‘holiday.’ And of course, on the big day, there was 100% cloud cover and it was so cold we had to wear gloves.

One night, me and the chap were out in Sefton Park, Liverpool, admiring a wonderful conjunction of several planets dancing around a new moon like fairy lights. Flushed with happiness, we went in and congratulated ourselves for figuring out how to use a planisphere.  Next morning we were mortified to find out aurora had been visible ten minutes after we went in.

And indeed, only last week, I was photographing some incredible clouds where I live in Bristol, only to be told a short while later that even more aurora had decided to shimmy their way on to the sky’s stage while I had my back turned.

I travelled to America last year, and on my first night, I was so jetlagged that I shut the blind to keep out an incredibly bright moon. Mr Moon was very cross at my ignorance, and proceeded to turn bright red with rage, causing me to miss a spectacular lunar eclipse.

But the thing I have had the LEAST luck with…is meteor showers. I have stood out in back gardens and dark fields trying to catch a glimpse of these fleeting sky streaks at least three times a year from the age of 15. And guess what? Except for ONE Leonid I saw, cutting through soupy orange cloud two years ago, I have not had ANY luck. Truly disheartening.

That is, if you forget about last year. I was in Portland, on the west coast of America. Through a set of remarkable coincidences, which really do make me wonder if we are being pulled through our lives by twinkling cosmic threads, I ended up meeting some wonderful people who shared my love of all things that require tipping your chin up to 90 degrees to observe.

They took me out to a pitch-black nature reserve, bundled up with blankets and deckchairs, as bullfrogs boomed in the blackness, and baby racoons cavorted in the undergrowth.

On that magical, starry, starry night, we counted several hundred Perseids, each one causing me to gasp and grip the arm of my chair. One of the most memorable experiences of my life and one I long to repeat.

So. Will I be turning my head skywards for the Perseids this year? Of course I will. But judging from past form, I’d say, chances are, Bristol is not going to enjoy clear skies. I just seem to have that unfortunate effect on the sky over my head.

So if there are any astronomers in the Bristol area hoping for a good viewing, you may want to drive me out of town with planks and pitchforks. Either that, or take a trip to Inverness.

Follow me for further antics on twitter, I am @RadioVicky

Originally posted on Dark Sky Diary by Steve Owens (@darkskyman on twitter)

Tonight (actually around 0130 tomorrow morning) the Full Moon will reach its highest point due south, just an hour and a half after the eclipse ends. Despite being at its highest in the sky, you’ll still struggle to see it, as it is very low down. In fact the Full Moon nearest the Summer Solstice is the lowest Full Moon of the Year

First, let’s begin with the definition of “Full Moon”. A Full Moon occurs when the Moon is diametrically opposite the Sun, as seen from the Earth. In this configuration, the entire lit hemisphere of the Moon’s surface is visible from Earth, which is what makes it “Full”. There is an actual instant of the exactly Full Moon, that is the exact instant that the Moon is directly opposite the Sun. Therefore when you see timings listed for the Full Moon they will usually include the exact time (hh:mm) that the Moon is 180° round from the Sun (we call this point opposition). Here’s a list of the times of all Full Moons between June 2011 and June 2012:

* UK observers should add on one hour for BST As you can see from this table, the instant of the Full Moon can occur at any time of day, even in the daytime when the Moon is below the horizon. So most often when we see a “Full Moon” in the sky it is not exactly full, it is a little bit less than full, being a few hours ahead or behind the instant of the Full Moon. I’ll refer to this with “” marks, to distinguish this from the instant of the Full Moon (they look virtually identical in the sky). The Moon rises and sets, like the Sun does, rising towards the east and setting towards the west, reaching its highest point due south around midnight (although not exactly at midnight, just like the Sun does not usually reach its highest point exactly at noon). And like with the Sun the maximum distance above the horizon of the “Full Moon” varies over the year. The Sun is at its highest due south around noon on the Summer Solstice (20 or 21 June) and at its lowest due south around noon on the Winter Solstice (21 or 22 Dec) (of course the Sun is often lower than this, as it rises and sets, but we’re talking here about the lowest high point at mid-day, i.e. the day of the year in which, when the Sun is at its highest point that day, that height is lowest…) And because Full Moons occur when the Moon is directly opposite the Sun, you can imagine the Moon and Sun as sitting on either sides of a celestial see-saw: on the day when the Sun is highest in the middle of the day (in Summer), the Moon is at its lowest high point at midnight; and on the day when the Sun is at its lowest high point in the middle of the day (in Winter), the Moon is at its highest high point at midnight. This means, in practical terms, that Summer “Full Moons” are always very low on the horizon, while Winter “Full Moons” can be very high overhead. Here’s a table of the altitude of the “Full Moon” when due south. Remember the times in this table don’t match the exact time of the Full Moon, but instead have been chosen as the closest in time to that instant, and so have be labelled “Full Moon” (in quotes).

* UK observers should add on one hour for BST ** The altitude here is based on my observing location in Glasgow, Scotland. You can find out how to work out how high these altitudes are here. As you can see from this table, the highest “Full Moon” due S this year occurs at 0030 on 11 December 2011, when the Moon will be over 56° above the southern horizon (approximately the height of the midsummer mid-day Sun which culminates at 57°34′). Compare this to the “Full Moon” this month, just after the eclipse, in the morning of 16 June, when the Moon barely grazes 10° above the horizon, and you can see just how low the midsummer Full Moon can be. In fact the closeness of summer “Full Moons” to the horizon means that this is an ideal time of year to try and observe the Moon Illusion.  

Originally posted on Dark Sky Diary by Steve Owens (@darkskyman on twitter)

Today, 13 June, is one of only four days in the year when the time as read on a sundial will be exactly correct.

Sundials usually tell the time using the shadow of the gnomon as cast by the Sun. This is possible as the Sun appears to move across the sky at an approximately constant speed, and so the shadow of the gnomon also moves at an approximately constant speed. The inconstancy of the Sun’s apparent motion in the sky – and therefore of the gnomon’s shadow on a sundial – is the subject of this article, and is calculated using the Equation of Time.

If you look at the shadow of a sundial’s gnomon it will fall onto a curve of numbers, along hour lines indicating local solar time. This is not equal to the official clock time until three important corrections are made:

Please read the rest of this article on Dark Sky Diary

Originally posted on Dark Sky Diary by Steve Owens (@darkskyman on twitter)

The first total eclipse of the Moon of 2011 occurs this Wednesday evening, 15 June 2011, and it will be the longest lunar eclipse in over a decade. However the views from the UK (and Europe) will be constrained by the fact that the Moon will be below the horizon for much of the eclipse, and will rise fully eclipsed, or in some cases even coming out of eclipse. It’s still worth having a look though: just try to find somewhere with a very low and clear SE horizon, as this will be the direction in which the Moon will rise, and it will be in eclipse only while it is VERY low (only a few degrees above the horizon).

A lunar eclipse occurs when the Moon, in its orbit around the Earth, passes into the Earth’s shadow, as cast by the Sun. You might imagine that this would happen once every lunar orbit, or once a month. That it does not is due to the fact that the Moon’s orbit around the Earth is tilted by around 5 degrees compared with the Earth’s orbit around the Sun. So in most orbits the Moon passes above or below the Earth’s shadow.

Please read the rest of this article on Dark Sky Diary

Originally posted on Dark Sky Diaries by Steve Owens (@darkskyman on Twitter)

The Channel Island of Sark has been recognised for the quality of its night sky by the International Dark-sky Association (IDA), who have designated it the world’s first dark sky island, the latest in a select group of dark sky places around the world.

Sark has no public street lighting, there are no paved roads and cars, so it does not suffer from the effects light pollution in the same way as towns and cities do. This means that the night sky is very dark, with the Milky Way stretching from horizon to horizon, meteors streaking overhead, and thousand of stars on display.

Caption: “Stargazers on Sark enjoy the wonder of the Milky Way”. Image Credit: Martin Morgan-Taylor

The announcement was hailed as a great success by astronomers. Prof Roger Davies, president of the Royal Astronomical Society, said: “This is a great achievement for Sark. People around the world are become increasingly fascinated by astronomy as we discover more about our universe, and the creation of the world’s first dark sky island in the British Isles can only help to increase that appetite. I hope this leads to many more people experiencing the wonders of a truly dark sky”.

The award follows a long process of community consultation, which included the assessment of the sky darkness and an audit of all the external lights on Sark. A comprehensive lighting management plan was created by lighting Jim Patterson of the Institute of Lighting Engineers, and many local residents and businesses have altered their lighting to make them more dark sky friendly, ensuring that as little light as possible spills upwards where it can drown out the starlight.

Caption: “The Milky Way above the Seigneur’s Mill on Sark”. Image Credit: Martin Morgan-Taylor

The government of Sark, the Chief Pleas, were supportive from the start. Conseilleur Paul Williams, chair of the Agriculture Committee, which oversees environmental matters, said: “Sark becoming the world’s first dark sky island is a tremendous feather in our environmental cap, which can only enhance our appeal. Sark is a wonderful island and this recognition will bring our uniqueness and beauty to a wider audience.”

This designation means that Sark joins the select group of international sites chosen for their dark skies, including Galloway Forest Dark Sky Park, which became Europe’s first International Dark Sky Park in November 2009.

Steve Owens, the dark sky development officer who led Sark’s application to the IDA, recognises the benefits that this might have for the community on Sark: “This is an ideal opportunity to bring stargazers to the island throughout the year, and I think that Sark is about to see a boom in astro-tourism, especially in the winter months. We’ve seen a surge of public interest in astronomy in recent years, with the International Year of Astronomy in 2009 and more recently with the success of BBC Stargazing Live, and it’s great that places like Sark and Galloway Forest Dark Sky Park are allowing people from towns and cities to come and experience a dark sky”.

FURTHER INFORMATION

Sark Tourism: http://sark.info/

International Dark-sky association: http://www.darksky.org/

Campaign for Dark Skies: http://www.britastro.org/dark-skies/

Originally posted on Sky and Telescope by by Kelly Beatty, October 6, 2010

Everyone enjoys a great meteor shower, those special times each year when a profusion of shooting stars zip across the sky. So here's a head's up: all of you should circle October 8th on next year's calendar.

This is the yearly date when Earth plows through a tenuous band of space dust created by Comet Giacobini-Zinner along its orbit. Ordinarily, the Draconid shower (formerly called the Giacobinids) puts on a so-so celestial show, delivering about 20 meteors per hour if you can view them under a moonless, pitch-black sky. That's hardly worth staying up for: after all, from a similarly clear, dark site you'll see six or seven random ("sporadic") meteors per hour.

However, this shower has a Jekyll-and-Hyde personality. In 1933 and 1946 the Draconids dazzled skywatchers with astounding meteor "storms" — delivering shooting stars at rates that briefly topped 10,000 per hour! — because Earth crossed through a particularly dense ribbon of debris shed by the comet in 1900. The shower hasn't put on that kind of performance in the years since, though in 2005 it surged unexpectedly to double or triple the usual rate.

If celestial prognosticators are right, we're in for a treat next year, when Draconid rates could top 600 per hour — that's 10 per minute — under ideal viewing conditions. That surge is in the cards because we'll likely clip the stream of particles ejected in 1900. Odds are that it's still largely intact, even though the comet's 6½-year-long orbit periodically puts it in Jupiter's disruptive vicinity.
 

On October 8, 2011, Earth will pass through several streams of particles ejected over the past 200 years by Comet Giacobini-Zinner.

J. Vaubaillon & others

At a meeting of planetary scientists now under way in Pasadena, California, meteor dynamicist Jérémie Vaubaillon (IMCEE, France) put forth predictions that he'd calculated with colleagues Mikiya Sato and Jun-ichi Watanabe (NAOJ, Japan). If they're right, next October 8th Earth crosses some cometary debris shed by Comet G-Z between 1873 and 1894, peaking at perhaps 60 meteors per hour centered at 17:09 Universal Time, followed at 19:57 UT by a much stronger, 600-per-hour pulse from the 1900 stream.

The rate is very uncertain, Vaubaillon admits, because there's no way to know whether those earlier streams are still densely packed or have been spread thin. Meteor observing wasn't as rigorous back then as it is now. But next year's results should help disentangle which streams are still contributing to the overall rates.

Other meteor specialists are also struggling to come up with firm rates. In 2008 Sato and Watanabe independently estimated a maximum of 500 per hour (at 20:36 UT), whereas NASA researchers Danielle Moser and William Cooke have offered a more optimistic 800 per hour (at 19:11).

These times favor observers in Europe, but don't rush out to book a plane just yet. First, the Draconid shower tends to produce many faint meteors that'll be obliterated by a nearly full Moon that night.
 

Although Europe is favored for watching the 2011 Draconid meteor shower, this map of average cloud cover during October suggests finding clear skies might prove challenging. (Bluer hues denote more frequent clouds.) Click on the image for a larger view.

Jay Anderson

Second, because the shower's radiant is way up near the head of Draco (declination +54°), the best observing sites would likewise be geographically north. But there's a reason that so few people book vacations to Scandinavia in October: "Weather in Northern Europe is not very pretty," notes Canadian meteorologist Jay Anderson. "October can be very nice, but usually it is the time when the winter cloudiness begins to encroach on the daily weather."

Instead, Anderson's cloud-cover map (at right) suggests that the northernmost "good weather" spot is in the Greek Islands. "Santorini — a favorite place of mine — has clear/few/scattered cloud cover 74% of the time. I know where I'd go."

The Campaign to Protect Rural England (CPRE), in conjunction with the British Astronomical Association‘s Campaign for Dark Skies, has recently announced their 2011 Star Count Project.

Star Count Week 2011 (from CPRE website)

Star Count Week (Monday 31 January – Sunday 06 February 2011) aims to get you outside and looking up, specifically to assess how dark – or light – your sky is.

The technique is simple. 1. Find Orion. 2. Count all the stars you can see within the main rectangle formed by Betelgeuse, Bellatrix, Rigel and Saiph, the four stars that make up Orion’s shoulders and feet. (Don’t count the three bright belt stars). 3. Tell the CPRE.

That’s it. By counting how many you can see, astronomers can calculate your sky’s limiting magnitude, or the brightness of the faintest stars you can see. It’s a very simple – and rewarding – project to take part in.

There are other annual star count programmes, such as GLOBE at Night (March 22 – April 4 2011) which I blogged about during their 2010 event. You can also get more involved and conduct a detailed dark sky survey, or take part in local activities such as the Peak District National Park’s Orion in the Peak project

Originally posted on Dark Sky Diaries by Steve Owens (@darkskyman on Twitter)

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.

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.

Originally posted on Dark Sky Diary by Steve Owens www.twitter.com/darkskyman

At 1900 GMT on 3 January 2011 the Earth will be at perihelion, its closest approach to the Sun this year.

If that sounds confusing to you, and has you wondering why it’s so cold given that the Earth is at its closest to the Sun, then this belies (a) a northern-hemisphere-centric attitude (in the Southern Hemisphere it’s summer right now), and (b) a misunderstanding of what causes the seasons.

The Earth orbits the sun in a nearly circular orbit called an ellipse. The degree by which an orbit differs from a perfect circle is called the eccentricity, e. If e = 0 then the orbit is circular; if e = 1 then the orbit is parabolic, and therefore not gravitationally bound to the Sun. The Earth’s orbital eccentricity is 0.0167, meaning that it is very nearly circular, with the short axis of the ellipse being around 96% the length of the long axis.

Thus, during perihelion Earth is 0.983AU from the Sun, while during aphelion (its furthest distance from the Sun, occurring this year on 4 July) Earth is 1.017AU from the Sun. (1AU = 1 astronomical unit = the average distance between the Earth and the Sun = 150 million km). The seasons on Earth have really nothing to do with how close the Earth is to the Sun at different times of year. Indeed how could they, given that the difference in distance between closest and furthest approach is only a few per cent?

The seasonal differences we experience are of course caused by the tilt of the Earth’s axis, which is inclined by 23.5 degrees from the vertical. This tilt means that, as Earth orbits the Sun, for six months of the year one hemisphere tips towards the Sun, so that it experiences longer days than nights, becoming most pronounced at midsummer, at which point the Sun reaches its highest in the sky at noon. Simultaneously the other hemisphere tips away from the Sun, and experiences shorter days than nights, becoming most pronounced at midwinter, on which day the Sun is at its lowest noontime altitude.

Earth's tilted axis

The further you are from the equator the more pronounced the seasonal effects. In fact equatorial countries don’t experience seasonal variations, while the poles experience extremes with six-month-long winters and summers.

The timing of perihelion and aphelion relative to our seasons is entirely random. The fact the southern hemisphere midsummer (21 Dec) almost coincides with perihelion (3 Jan) is simply that; a coincidence. Given that fact, there is no reason to be surprised that perihelion occurs so close to northern hemisphere midwinter. it has to happen some time and it’s coincidence that it happens to occur within two weeks of midwinter / midsummer.

To take this explanation even further, we can calculate how much variation in incident sunlight (called the flux) there would be in two scenarios:

1. an imaginary scenario where the seasonal varioations in temperature are due to the tilt of the Earth’s axis but where the Earth goes round the Sun in a perfectly circular orbit

and

2. an imaginary scenario where the Earth’s axis isn’t tilted, but where it’s orbit is elliptical in the same degree as ours actually is.

1. The Sun appears at its highest point in our sky each day at noon. The highest it ever gets is at noon on midsummer. The lowest noontime altitude occurs at noon on midwinter.

In Scotland the Sun is around 55 degrees above the horizon at noon on midsummer, and only 10 degrees above it at noon on midwinter.

The amount of energy from the Sun radiant on a fixed area is proportional to the sine of the altitude, so the ratio of the solar energy radiant on a square metre of Glasgow between midsummer and midwinter is

sin(55) / sin(10) = 1.84

So here in Scotland we get 84% more energy from the Sun in summer than we do in winter, due to the tilt of the Earth’s axis.

2. If the Earth’s axis was not tilted, then we would only experience temperature differences from the Sun depending on how far or near we are from it. In this case, the amount of energy from the Sun radian of a fixed area is proportional to the square of the distance from the Sun, so the ration of the solar energy radiant on a square metre of Glasgow between perihelion and aphelion is

(1.017/0.983)^2 = 1.07

So we get 7% more energy from the Sun at perihelion than we do at aphelion., due to the differing distances to the Sun.

From this you can see that, while the distance to the Sun has some effect on how much heat we receive, it is a very small effect compared to that produced by our axial tilt.