Night Shining Clouds

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A few weeks either side of the summer solstice is the best time to observe ‘noctilucent’ or ‘night shining’ clouds.

These wispy collections of ice crystals are the highest clouds on Earth, located in the mesosphere up to 50 miles overhead. They’re too faint to be seen in daylight and best observed when the Sun is between -6 and -12 degrees below the horizon.

At the moment at Highland latitudes this gives you an approximate window between 11.30pm and 3am in the morning.

Clear skies.

Scotland – Land of the ‘almost’ Midnight Sun

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A stunning sunset captured over the Isle of Rum

In the north of Scotland we’re about four days away from losing all astronomical twilight and entering a period of sustained ‘nautical twilight’.

During this time the centre of the Sun’s disk never dips more than 12 degrees below the horizon, rendering our clear night skies a dark azure blue, with only the Moon, planets and brightest stars visible after midnight.

This will continue until mid July when astronomical twilight finally reappears.

Contrast this with London, where astronomical twilight continues right through mid summer, producing much darker night skies, but arguably less beautiful and prolonged sunsets.

Clear skies.

Inverness

We’re leaving astronomical twilight behind for several months here in the north of Scotland

London

Significantly darker night skies persist through mid summer in southern England.  Here’s the contrasting data for London.

The Winter Sun at Clava Cairns

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Looking south west from inside the north east cairn at Clava

As a family we have a yearly tradition of heading out for a longish walk on Christmas Eve.  We usually park up somewhere remote in the van, make some bacon rolls then head out along a forest trail or up a local hill.  This year we decided to see if we could catch the setting Sun at Clava Cairns, a beautiful bronze age site located only a mile or so from Culloden battlefield near Inverness.

During my astronomy outreach I’ve given quite a few talks referencing Clava Cairns in relation to the fascinating subject of ancient astronomy.  Often wild speculations are made about many prehistoric sites, in particular Stonehenge, with dubious claims of alignments to stellar constellations or complex planetary cycles.  But one thing is almost universally agreed by archaeologists and astronomers alike, that many of these ancient structures were configured to mark the passage of the solar year.

In Clava’s case, both main passage cairns have mid winter setting sun alignments facing towards the south west, such that for several days either end of the shortest day, the light from the setting Sun will shine down the central passage and light up the interior of the structure.

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Sun rays striking the winter solstice aligned passage.

Of course it’s one thing to read second hand accounts of this phenomena, and quite another to experience them first hand.  As luck would have it, when we approached the site around 3.30pm the Sun was clearly visible and just setting in the south west, allowing us to witness this amazing spectacle and to capture some photographs.

From inside the north east cairn, closest to the main entrance of the site, the passage was already brightly washed over with sunlight.  I was curious to determine if the sun’s position was low enough to light the passage when it was originally covered over (several thousand years ago), so crouched down within the passage to take some of my shots.  Sure enough, the rays of the Sun could be directly sighted down the camera lens.

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My daughter Violet standing in the sunlight directed down the main passage of the north east cairn.

The motivation for the astronomical alignment of these structures is still the topic of heated debate amongst historians and archaeologists, but one thing residents of the north of Scotland can appreciate first hand is the depressingly short days and long hard winters we experience at this time of year.  Some sort of large scale and perhaps communal confirmation that the south westerly extreme of the winter sunset (and its associated low midday elevation) had been reached would have been very reassuring to early agricultural societies.

It’s this concept of the Sun both halting its low elevation in the south at midday and the most southern extreme of its setting and rising positions that gives rise to the word Solstice – ‘sol ‘ sistere’ meaning Sun standstill.  The reverse applies during mid summer when the sun rises and sets at its most extreme positions to the north of east and west, and reaches its highest elevation at midday.

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The two main passage cairns at Clava have south westerly mid winter sunset alignments.

There are some researchers who go much further, and point to alignments between the stones at Clava Cairns with the Celtic cross quarter days and the more complex dynamics of major and minor lunar standstills.  Whilst these may be true it should also be remembered that it only takes two points to make a straight line!  As ever we need to be cautious with our wish to believe, and back everything up, where possible, with evidence.

Mercury and Jupiter Conjunction

 

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Have you ever seen the planet Mercury with your own eyes? It’s notoriously difficult to catch being situated so close to the Sun and often hard to pinpoint. You’ll only ever see it as a tiny disc in binoculars, very close to sunrise or sunset.

Over the next couple of days, centred on the Dec 21st solstice, there’s a unique opportunity to see Mercury as it forms a conjunction with bright Jupiter low in the south east in morning skies.

You’ll need a good unobstructed horizon to the SE to catch it. Use Venus as a guide to first find Jupiter, then look through your binoculars and you should see Mercury sitting above.

The window is pretty narrow, from around 7.30pm to 8.30pm. The longer you wait the higher Mercury will rise but the brighter the sky, as the Sun rises.

Good luck and clear skies.

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Mercury through a 10 inch telescope

Venus Morning Star

The planet Venus is a brilliant morning star at the moment. Catch it rising in the south east ahead of the Sun between 5.30am and 7.30am.

With keen eyesight and binoculars you should be able to discern Venus’s phase, currently a beautiful crescent. A telescope will make this much clearer as demonstrated by this video footage I shot last year, when Venus was ‘the evening star’.

Over the month of November Venus will get brighter as its phase waxes from a thin crescent to a 25% illuminated disc at month end.  Despite this brightening Venus is actually travelling away from us and after December 2nd its brightness will begin to diminish as it pulls further away from earth and its disc size shrinks .

Once Venus passes behind the Sun it will eventually reappear as an evening star around mid August 2019.

Clear skies!

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