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Nacreous Clouds

February 2, 2016 Leave a comment

Twitter was a-buzz yesterday evening (1 Feb 2016) and this morning, as users took snaps of a very rare display of Nacreous Clouds over the UK.

These clouds, also known as Polar Stratospheric Clouds, form high up in our atmosphere (in the stratosphere) between 15 and 25 km in altitude. Normally this part of our atmosphere is very dry but in polar winter temperatures can plunge and conditions can become right for certain clouds to form.

The following pictures were just some of those re-tweeted by @Virtualastro last night; give him a follow to keep up to date.

Nacreous Clouds (named that after the word “nacre”, for mother-of-pearl, due to their iridescent colours) appear when sunlight is scattered through the cloud, and particles within the cloud then produce colours through diffraction processes, making for a beautiful display.

To see a display of Nacreous Clouds you have to head out when the Sun is below the horizon – but only just – during Civil Twilight –  when the Sun is between 0 and 6° below the horizon. Look towards the direction of sunset or sunrise (depending on whether you’re out in the evening or morning), you may see these beautiful clouds for yourself.

Find out your civil twilight times at timeanddate.com. For central Scotland (where I am) the best time to see these clouds is between 0730-0810 and 1650-1730. Remember, these clouds are incredibly rare – you can go years without seeing such a display – and there’s no way to predict whether you’ll see them on any given night, but as they happened last night there’s a good chance they might happen again tonight or the following night, 2 or 3 Feb 2016. Get outside and look up!

 

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Morning Conjunction: Venus and Jupiter, August 2014

August 16, 2014 Leave a comment

On Monday morning, 18 August 2014, in the eastern sky before sunrise you’ll see a very close conjunction of the two brightest planets, Venus and Jupiter.

They’ve been shining brightly in the pre-dawn sky for a while now, but as they trace out their separate orbits around the Sun they appear to move relative to one another, Venus the faster of the two. And they’re getting closer every day, until on Monday 18 August they’ll be at their closest, only 12 arcminutes apart, about one third of the diameter of the Moon.

This is closest conjunction in 15 years, and will be a very striking sight in the morning sky, but you’ll need to be up and about early to see it, about an hour before sunrise, around 0450 BST (sunrise is around 0550BST for most of the UK – Orkney gets an earlier sunrise at 0535, while the southwest of England have to wait till around 0605).

If you’ve got a pair of binoculars and a tripod, or even better a telescope, it’s really worth looking at these two planets. Venus is the brighter of the two, shining about twice as brightly as Jupiter through the morning twilight, but if you can magnify them (and you’ll catch them in the same field of view in a pair of binoculars), then Jupiter will be around three times the diameter of Venus (30 arcseconds compared to 10), and you’ll see Jupiter’s four largest moons as tiny points of light near the giant planet.

Don’t worry if you’re clouded out, or if you sleep in, on Monday morning; they’ll be close together in the pre-dawn sky for a few days afterwards too.

Venus-Jupiter conjunction this morning, 0450BST 16 August 2014

Venus-Jupiter conjunction this morning, 0450BST 16 August 2014

Screenshot 2014-08-16 17.42.53

Venus-Jupiter conjunction 0450BST 17 August 2014

Venus-Jupiter conjunction at its closest, 0450BST 18 August 2014

Venus-Jupiter conjunction in close up, 0450BST 18 August 2014

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

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