New Moon on Christmas Eve

    Mark Thompson Astronomy Mark Thompson Astronomy | 12:00 PM, Saturday, 24 December 2011

    Distance travelled ~ 919'776'000 km

     

    Ever wondered why the Moon seems to look different at varying times of the month and sometimes, like today, seems to have totally vanished?

    (SORRY SANTA NO FULL MOON TONIGHT...)

    santa at christmas eve

    (Image courtesy of Dry Icons - http://dryicons.com)

    These are questions that perplexed mankind for centuries but the answer is actually not all that complicated.


    what the moon looks now

    Image credit: US Naval Observatory/Astronomical Applications Department. What does the Moon look like now?

    The first thing to understand is that we see the Moon because it reflects sunlight; turn the Sun off and the Moon would to all intents disappear from view.

     

    While the Earth is spinning and orbiting around the Sun, the Moon is orbiting around the Earth, completing one orbit in 27.3 days. Its actually more accurate to say that the Moon AND Earth orbit a common centre of gravity called the barycentre which lies inside the Earth but not at its centre. Because the Moon orbits the Earth, and the Earth orbits the Sun its easy to see that the actual angle between the three objects varies throughout the lunar orbit and its this variation that leads to the 'appearance' of the phases of the Moon.

    At the start of this blog, I stated that we see the Moon because it reflects sunlight. If the Moon lies opposite the Sun in the sky then we see the fully illuminated portion of the Moon and see a full Moon. If on the other hand, the Moon is between us and the Sun then we see the non-illuminated portion and see a new Moon. Then at various points between we see a varying amount of dark and light portions as the phases change from full to new and back again. Today the Moon is at its new phase which means its in line with the Sun and can't easily be seen without sophisticated equipment.

    You might expect that during either a full or new Moon, we should experience a lunar or solar eclipse every month (the Moon blocks sunlight reaching Earth during a solar eclipse and the Earth blocks sunlight reaching the Moon during lunar eclipses) but it turns out that the orbit of the Moon is tilted by about 5 degrees to the orbit of the Earth around the Sun. On most occasions at full or new Moon, the Moon is either just above or just below the Sun or shadow cast by the Earth, making eclipses a little more rare.

    Interestingly if you measure the time it takes from one full Moon to the next it takes 29.5 days instead of 27.3! This strange effect is seen because the Earth is independently orbiting the Sun and the Moon has to travel a little further to get back to exactly the same angle as the previous full Moon.

    Photo of the day: September's Northern lights

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    Aira Idris Aira Idris | 14:00 PM, Tuesday, 13 September 2011

    Distance travelled ~ 657'564'800 km

    northern lights 9 september

    Image taken by Bob Johnson, Saskatoon Saskatchewan, Canada, September 9 2011 with a Canon 40D camera and Tokina fisheye lens. "All the Solar activity happening lately causing all the Auroras, even with a nearly Full Harvest Moon they came through."

    To submit your images and video into 23 Degrees for a possible feature or for Friday's 'weekly roundup blog' - email them to 23degrees@bbc.co.uk or add them to the weather photography pool.

    Next few days of rain in UK great for rainbow appreciation

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    Helen Czerski Helen Czerski | 15:30 PM, Thursday, 11 August 2011

    Distance travelled ~ 572'823'200 km

    What is a rainbow?

    We all love rainbows. Even though we take it for granted that the sky changes colour all the time, there's something about these enormous semicircles that makes us want to smile, point and take photographs. And they're worth looking at, because you're seeing nature's paintbox directly. The entire spectrum of visible light is in there, and every single thing that we can see comes to us as a combination of those colours.

    The next few days could be great for rainbow appreciation, especially on Saturday and Sunday. A mixture of sunshine and rain is forecast for all of the UK, as several weather fronts pass over us.


    met office rain forecast 13 aug 2011

    Image courtesy of the Met Office

    So keep your eyes on the sky, and if you see bright sunshine appearing suddenly after a shower, turn away from it so that you are facing your shadow. If you're lucky, you'll then be looking at a giant arc of colour.

    A rainbow is a beautiful example of physics in action. The only ingredients are direct sun and water droplets (rain or mist) some distance away. When sunlight travels into these water droplets, it changes direction (this is called refraction) and the important part is that the path of blue light is bent a bit more than red light. We see sunlight as white, because it's a mixture of all the visible light colours. When sunlight goes into water droplets, bounces off the inside once and then comes out, the blue light comes out at a slightly different angle to the red light. You can only see a rainbow when the sun is behind you, and that's because the light that goes into those droplets and bounces once comes out at about 40 degrees to the direction it went in. The different angles of red and blue light mean that you have to look a bit higher up to see droplets which are sending red light in your direction - that's why red is on the outside of a rainbow.

    A rainbow is a very personal thing. Imagine a line that comes from the sun, goes through your head and then keeps going forwards in front of you. You will see a rainbow 40-42 degrees away from that line, and it would be a full circle if the ground didn't get in the way. But the person standing next to you is seeing a different rainbow, because the line joining their head and the sun is a different line. They see the colours from different droplets. You are the only person who can see your rainbow. This is why you can never get to the end of a rainbow - if you move closer to where you think the end is, the rainbow you see is a different one and you can't touch that one either.

    If you can't wait for the next shower to see all this, it's easy to make your own rainbow. All you need is a sunny day and a garden hose. I had a go last weekend with my mum wielding the hose (she also saw it as an opportunity to water the garden), and the photo I took is below. Stand with the sun behind you - the lower it is in the sky, the better - and get your helper to spray water a couple of metres in front of you. The shadow of your head will be at the centre of the rainbow circle. It'll be easier to see the rainbow if there's a darker background - in the photo below you can see that the rainbow is easier to see against the darker plants. A rainbow in the sky is exactly the same, but bigger because it's further away.

    home made rainbow

    Even though a rainbow looks ethereal and delicate, bear in mind that the energy from the sun carried by those colours is what powers our world.

    If you happen to spot any rainbows over the next coming days, send them to 23degrees@bbc.co.uk

    Even with the full moon there's hope left in the Perseid meteor shower

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    Mark Thompson Astronomy Mark Thompson Astronomy | 10:00 AM, Wednesday, 10 August 2011

    Distance travelled ~ 569'660'800 km

    GUEST POST

    (Mark Thompson is the BBC One Show's Astronomer and when not reporting for them, he is most likely writing about the sky or looking at it! You will often find him zooming in on, or through it, as not only is Mark an enthusiastic astronomer but he is also a qualified pilot. January 2011 saw Mark as part of the successful BBC Stargazing Live Presenting team. He also regularly writes for Discovery.Com and a host of other astronomy and space websites and will be producing a monthly space watch blog for 23 Degrees.)

    Morning Meteors of the Perseid Kind
    Image taken by Michael Menefee 7 August, Larimer County, Colorado, US. The peak of the meteor shower should make visible 20-30 per hour.

    It may not seem like it but the Earth is hurtling around the Sun at the breakneck speed of about 107,000 km per hour. We don't often get a chance to see evidence of this motion but around the middle of August every year, something happens which gives it away. Planet Earth passes through a field of debris that has been left by Comet Swift-Tuttle as it orbits around the Sun which gives rise to one of natures most amazing spectacles, the Perseid meteor shower.

    There are about 30 different meteor showers each year where the Earth passes through the debris left by other comets and they happen at broadly the same time every year. If you watch the meteors carefully during any particular shower, you may notice that they all seem to come from one point in the sky, we call this the radiant. They don't actually come from one point in space, its a visual effect arising from something we call perspective. You can see a similar effect if you stand on a bridge over a motorway, all the parallel lanes seem to come from one point on the horizon. The location of the radiant determines the name of the shower, for example the radiant for the Perseid shower sits in the constellation of Perseus.

    During the shower, you can expect to see a number of fast moving lights zipping, unannounced across the sky, all seeming to come from Perseus. These lights are produced as tiny pieces of rock slam into our atmosphere at speeds in excess of 200,000 km per hour. On hitting our atmosphere the gasses in front of the rock get compressed to such a degree that they give off the characteristic flash of light. Typically, most of the pieces of rock (meteoroids) will burn up high in the atmosphere and when they do we call them meteors, if they are big enough to land then they are called meteorites.

    This year then, in the early hours of 13th August, we will be treated to the peak in activity of the Perseids although it is possible to see meteors from this shower from now until the end of the month. Unfortunately the Full Moon will be present overnight on 12/13 August which means its bright light will block the fainter ones from our view. The best thing to do is get outside, away from bright street lights anytime before dawn between now and then and you should see plenty. Its best to look for them in the early hours as you are then on the front face of the Earth as it moves through space. Its a bit like all the flies you find stuck to your car windscreen but hardly any on the back window. Wrap up warm and set up a comfortable chair outside, lay back and watch. If you are lucky and you do see some, don't forget to make a wish.

    If you plan on viewing the show, send your pictures in to 23degrees@bbc.co.uk

    Double CME hit Earth's magnetic field 5 August producing beautiful Auroras

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    Aira Idris Aira Idris | 11:00 AM, Monday, 8 August 2011

    Distance travelled ~ 564'622'400 km

    auroral display Scotland

    This photo was taken on August 5, 2011 in Elgin, Scotland, by Alan Tough.

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