Archives for June 2011

Noctilucent clouds spotted at lower altitudes

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Aira Idris Aira Idris | 17:30 PM, Thursday, 30 June 2011

Distance travelled ~ 465'586'300 km: day 181

Noctilucent clouds are a summertime phenomenon which were first observed in around 1885. Noctiluscent [ the name means night shining in Latin ] are high wipsy clouds made of tiny crystals of water ice up to 100 nanometers in diameter. They are the highest clouds in the Earth's atmosphere, occurring in the mesosphere at altitudes of around 76 to 85 kilometers (47 to 53 mi).

Noctilucent Clouds in the Wake of the Eclipse

Image courtesy of Brendan Alexander/Flickr, Ireland, June 15 2011

Noctilucent Clouds in the Summer Sky

Image courtesy of Brendan Alexander/Flickr, Ireland, June 15 2011

Clouds in the Earth's lower atmosphere form in a process called nucleation when water gathers on dust particles, but Noctiluscent clouds also form directly from water vapour as well as forming around on dust particles. It is unclear where the dust or water in the mesosphere comes from but it's thought that the particles may be from dust from micrometeors, although some scientists think dust from volcanoes may also be involved. The source of the water is equally unclear as the mesosphere contains very little moisture - approximately one hundred millionth that of air from the Sahara desert but it's possible that the water comes from lower in the atmosphere or from chemical reactions in the upper atmosphere. This water vapour freezes directly into ice crystal to form the clouds in the thin upper atmosphere when temperatures drop to about -120 °C (-184 °F).

For many years Noctiluscent clouds were a very rare sighting, but over the past 20 years they have become more common. Originally confined to the higher latitudes they are increasingly observed in lower latitudes nearer the equator. So why are they becoming more common and reaching lower latitudes?

Nasa's AIM satellite mission (Aeronomy of Ice in the Mesosphere) which launched in 2007 was set up to study the Noctilucent clouds and to answer these questions.

Dr James Russell at the University of Hampton explains to me some of the findings of the AIM mission (James Russell III of Hampton University, Hampton, Va. Is AIM's principal investigator):

"Noctilucent clouds are the highest cloud in the Earth's atmosphere forming in the mesosphere at high altitudes (approximately 76 to 85 kilometers, or 47 to 53 miles). It seems odd that they are a summer time phenomenon when they feed off extremely cold temperatures, however as heat warms the air near the ground, the air rises. As it rises, it also expands since atmospheric pressure decreases with height ( temperatures in the mesosphere down past a freezing -210º F (-134 ºC).

We are still unsure exactly why they are increasing in lower latitudes or showing up brighter, they are like a geophysical light bulb, you go from no clouds to full formed clouds in days. This may be due to a sudden change in temperature at the altitude that these clouds are formed. They form in an atmosphere with 100 times lower pressure than at earth surfaces.

During the summer season the temperature stays very low at the poles. For a long time we thought the increase in frequency was a result of temperature decrease but now our research is leaning more to water vapour. Increase in water vapour increases the frequency of clouds. The primary reason for more water vapour at higher altitudes is methane which we are most likely responsible for.

Our research still has far to go however. We have been at solar minimum whilst the AIM mission has been out. Heating is different and dynamics is different so we need to continue our research for a full solar cycle."

The mission has now been extended until 2014 and Dr Russell thinks that the additional research may show a link between frequency in Noctilucent clouds and human activity and that this data may prove helpful to climate scientists investigating climate change.

Delights of the summer Sky: Noctilucent Clouds & Iridium Flare

(The wonderful views of the processing NLC display were interrupted by no less than 3 majestic passes of the ISS. Finally as the Sun was creeping towards the horizon the brilliant Jupiter came into view in the north eastern twilight. Upon return to my home when reviewing my photos I realised I captured an Iridium flare along with the NLC. A great ending to a truly magical night. June 15 2011)
Image and caption courtesy of Brendan Alexander/Flickr, Ireland, June 15 2011

Newly discovered asteroid: 2011 MD closest approach 17.03 UT (just above 12,000km)

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Aira Idris Aira Idris | 17:00 PM, Monday, 27 June 2011

Distance travelled ~ 457'958'400 km: day 178

asteroid 2011 MD

Image courtesy of NASA

(At closest approach, 2011 MD will pass in broad daylight over the southern Atlantic Ocean near the coast of Antarctica. As the asteroid recedes from Earth, it will pass through the zone of geosynchronous satellites. The chances of a collision with a satellite or manmade space junk are extremely small, albeit not zero.)

Is it really a spanish plume?

Aira Idris Aira Idris | 16:00 PM, Monday, 27 June 2011

Distance travelled ~ 457'958'400 km: day 178

Today is set to be the hottest day in the UK so far for this year, surpassing yesterday's 30°C. It's not all sunshine however as thunderstorms, hail and possibly tornadoes have also been forecast for later today. But what's causing this combustible mixture of heat and storms?

The favourite explanation seems to be the evocatively named "Spanish plume". It's an event that occurs once or twice a year on average, but in recent years has been less frequent.

'Spanish Plume' is actually a rather catchy name for a complex meteorological phenomenon which leads to warm conditions and heavy showers or thunderstorms over parts of the UK and north-west Europe.

A classic Spanish plume consists of very warm air that pushes north from around the vicinity of Spain towards the British Isles. Not surprisingly, that hot Mediteranean air warms us up. But then this air mass meets with cooler Atlantic air coming from the West - the kind of air that normally affects the UK. The plume air is pushed up over the cooler Atlantic air, and this produces thunderstorms.

Because the Spanish plume can cover a large area the accompanying storms can give widespread, heavy rainfall, often accompanied by hail.

But are we seeing the key ingredients for a Spanish plume now? According to the Met Office we are not. What we have at the moment is a warm area across the east of the UK - not from the Mediteranean. This warm air is encountering a cold front pushing across from the West, bringing showery rain.

This is different from a Spanish Plume according to Dave Britton at the Met Office, because for a classic Spanish plume you need to have warm, dry air push up from the south. This acts as a lid on local showers because the air can't rise through the lid. Eventually the rising currents of air get strong enough to break through this lid, and by now they're violent enough to develop into thunderstorms.

So although great weather for fans at Wimbledon today with Andy Murray's win, it seems our current weather is not due to the Spanish plume at all. Maybe somebody should think of a catchy title for warm air from the East meeting a cold front from the West?

Fingers crossed the storms pick up later for those heading out on a chase. Leave a comment or send the 23 Degrees team your updates and photos for a possible story or feature.

A date with History: Fram polar expedition leaves Norway June 24 1893

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Helen Czerski Helen Czerski | 16:30 PM, Friday, 24 June 2011

Distance travelled ~ 450'240'000 km: day 175 

Ice is an important contributor to our weather, but finding out about the Earth's ice was very hard work. It's still less than a hundred years since Amundsen first reached the South Pole (he arrived on the 14th of December 1911, beating Scott by 35 days). My favourite polar expedition is one that is rarely mentioned because it wasn't an expedition in the normal sense. It was made by a ship called the Fram, and there were no sleds or dogs, and there wasn't even any navigation. The Fram was designed to become a piece of pack ice, and it spent three whole years doing just that (from 1893-­‐1896). Its voyage was not only a fantastic oceanographic experiment but also an amazing illustration of the dynamic nature of the Arctic.



We tend to think of polar ice as being a bit like giant dollops of whipped cream on top of a dessert, as smooth white splodges that from space almost look as though they're about the run down the sides of the Earth. 

Ice at the South Pole is fairly static, but things are very different at the North Pole because the Arctic is an ocean, not a continent. In the Arctic ocean the ice is dense pack ice, always moving, breaking apart and reforming. Pushed by ocean currents below and by wind above, Arctic ice never gets to sit still. The ocean at the North Pole is about 4.2 km deep, and there's no flag there and no base because no piece of ice is ever over the North Pole for any length of time.

Fridtjof Nansen designed the Fram to test the theory that there was an ocean current that crossed the entire Arctic basin. He reasoned that if the jostling ice chunks were pushed along from one side to the other, a ship could be pushed along too. It would be a bit like a conveyer belt to the North Pole, and all he would need was patience and the right ship. The danger was that the ship would be crushed by the huge slow-­‐moving pieces of ice, so the Fram was designed with a very round keel so that it would be lifted out of the water and carried rather than crushed. This plan worked beautifully, except that the Fram never quite got to the pole. The ship and her crew were pushed about all over the place [link to map], eventually drifting to the edge of the Arctic ocean and freedom after three years. The furthest north she reached was nearly 86 degrees, 280 miles from the pole.

Even though she didn't get to the North Pole, the Fram clearly demonstrated the dynamic nature of ice in the Arctic, and we now know that individual pieces of ice can indeed travel from Siberia to Greenland in 3-­‐4 years, or can go round a sort of giant ice-­‐roundabout (called the Beaufort Gyre) in 7-­‐10 years. Most polar expedition stories are about humans struggling against natural forces to achieve their goal, but I like the Fram's exploits because they're about humans working with the enormous forces of this planet instead of against them. What are your favourite examples of that?

Will monsoons once again return to the Sahara?

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Stephen Marsh Stephen Marsh | 12:50 PM, Friday, 24 June 2011

Distance travelled ~ 450'240'000 km: day 175

africa's sahara desert

Image and notes courtesy of NASA

Image and notes courtesy of NASA
(On August 25, 2000, the Moderate-resolution Imaging Spectroradiometer (MODIS) acquired this spectacular image of a region in Africa's Sahara Desert, including the southern part of the border between Algeria and Libya. Three large rock massifs appear to be pushing up from beneath red sand dunes: from left to right are the Tassili, Tadrart-Acacus, and Amsak massifs. Different rock types account for rock colors varying from dark brown (Acacus) to the pale tone of Amsak eastern portion (Amsak Mellet means Pale Amsak in the local Tuareg dialect) The dendritic structures of ancient riverbeds are clearly visible in the Acacus-Amsak region.)

How did the Sahara once have a monsoon? Well it's all down to the amount of sunlight hitting the region. But not quite in the way you might think. It seems obvious that a hotter Sahara would have less rain, because it's the opposite. Monsoons are not created by less solar energy, they are created by more. To get a Monsoon you need lots of solar energy that heats up the land creating a region of low pressure to suck cool moist air from the oceans towards it. Strange as it may seem 8000 years ago when the cave paintings in Wadi Sora were made the Sahara was getting more sunlight than it is now. And that extra heat helped bring the monsoon rains to this desert. But how did the Sahara get more solar energy?

It's all down to our planets orientation to the Sun and how that changes over time. This orientation, which dictates the amount of sunlight we receive, is controlled by three main factors, Tilt, Precession and Orbit. 8000 years ago when the Sahara was green, these factors were different to what they are today. The science of this is very complex but here's a simple summary of what was going on.

Currently the earth tilts at an angle of 23.4 degrees. But over a 41,000 year period it changes, wobbling between 22.1 and 24.5 degrees. Back when the Sahara was green, the tilt was close to its largest possible angle, 24.2 degrees. Which meant that 8000 years ago the Sun shone more directly, more intensely over the Northern hemisphere.

Precession is even more important. This is not a change in the degree of the tilt, but a sort of lateral wobble, which changes the direction of the tilt. The best way of explaining it is by looking at the stars. Some of you may know about the North Star or Pole Star called Polaris. While other stars move across the sky, Polaris stays fixed just above celestial north. That's certainly true now but when the people painted themselves in the cave of swimmers, Polaris wasn't close to north in fact it was over to the east. Then 8000 years ago Thubon was the North Star. And in 12,000 years, a new star, Vega, will be pointing out due north. The North Star changes because precession makes the earth wobble a bit like a spinning top slowing down and starting to wobble back and forth. This precessional wobble takes 23000 years to complete one cycle, so it will be 23000 years before Polaris will come back round to be our northern star again.

There is one final factor involved. Our annual orbit around the Sun is not a perfect circle - it's an ellipse. Also the Sun does not sit at the centre, it's offset to one side. So there are times when it is closer to the Sun than others. Just like Tilt and Precession the shape of the orbit also changes slowly over time becoming more or less elliptical moving the earth closer or further from the sun. When the Sahara was green, all these orbital factors were in alignment, so summers in the northern hemisphere were hotter than they are now, the Sahara received more sunlight which pulled the monsoon band to northward.

The changes in our orientation to the Sun change all the time and gradually the orbit, tilt and precession changed so that the amount of solar energy hitting the Sahara eventually decreased and with it the monsoons.
Around 6000 years ago, the monsoons failed completely, the rains stopped, the rivers dried up and the land began to turn to desert. But even as you read this the same orbital factors are slowly changing and at some point in the future they will align again and the monsoons should once again return to the Sahara.

But that's not the end of the story because scientists have discovered that the wet period 8000 years ago wasn't a one off, in fact it had happened many times before. Perhaps the most significant greening of the Sahara occurred 120,000 years ago at a particularly important moment in human history.

120,000 years ago homo sapiens, modern humans, emerged from Africa. For thousands of years the Sahara had been an impassable barrier, a bit like it is now. But 120000 years ago the evidence suggests the Sahara was green and criss-crossed with rivers and lakes, and scientists believe that it allowed passage for our ancestors north. They crossed the Sahara travelling along rivers and settled in North Africa, and eventually, Europe and Asia.

It really is incredible to think that such critical moment in our history could have been triggered by changes in our tilt and orbit.

Jacana Productions out with CSWR: Tornado Osceola NE, 20/06/2011 [VIDEO]

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Aira Idris Aira Idris | 17:50 PM, Thursday, 23 June 2011

(Whilst the 23 Degrees team were trailing the Centre for Severe Weather Research DOW's on Monday 20 June in Nebraska, this amazing footage of the massive tornado was captured by Jacana productions team. For licence of this video please contact them directly)

A green savannah from an arid desert: 23 Degrees team heads to the Sahara

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Stephen Marsh Stephen Marsh | 15:45 PM, Thursday, 23 June 2011

Distance travelled ~ 447'667'200 km: day 174

Today Kate Humble and the 23 Degrees team are in Egypt heading deep into the Sahara desert to one of the most fascinating most magical places on the planet. It's a place that holds clues to the extraordinary history of this part of the world.


The team are travelling from Luxor into the Sahara close to the borders of Libya and Sudan. It's a two-day trek across barren desert with temperatures hitting the high thirties and the low forties on a regular basis. The expedition has half a dozen jeeps, a military escort of Egyptian soldiers and enough provisions and water to last a week.

From Luxor their first stop is the Dahkla oasis, the last bit of civilisation for many hundreds of kilometres. From here on it's camping under the stars.

From Dahkla the team travels across endless white dunes until they reach a region of red sand, hills and ravines leading to a vast plateau rising up 300 metres. It's called the Gilf Kebir or Great Barrier. If you've read the book or seen the movie The English Patient, that might recognise the place as it features heavily in the story. In fact back in the 1930s the Gilf was explored by Hungarian adventurer Count Lazlo Almasy the inspiration for the main character in the book and film. He was looking for the legendary lost city of Zerzura. He didn't find Zerzura, but he did stumble across something that changed our understanding of the history of the Sahara. And that's what Kate and the team are heading towards.

Hidden in a gorge called Wadi Sora is one of humanities great treasures, the legendary and magical Cave of Swimmers. It is full of amazing drawings that are at least 8000 years old. There are over 300 figures; some are of hunters carrying bows. There are giraffes and deer even hippos.

There are dozens of handprints and footprints, created by blowing of coloured powder over the hands and feet. And within the many images is an extraordinary image of a child's hand inside an adult's hand, perhaps their father or mother. It's an incredible, romantic message reaching out to us from many millennia ago.

These paintings show that people once lived here, perhaps nomadic families who hunted the animals they depicted in the cave. But another image tells us something more about this region 8000 years ago. There is one painting that shows people swimming, giving this cave its name.

This particular image shows that once this region had water, lakes and rivers. So how does a desert become a lush savannah and a green savannah turn back to arid desert? To find out Kate and the team travel to another gorge about a days drive away called Wadi Bahkt. Cut into the surface is an 8-metre crack showing layer on layer of sediment. These sediment layers are created by seasonal rains. It's clear evidence that at one point this part of the Sahara had annual rains called Monsoons large enough to create rivers and lakes, with one believed to be the size of Belgium.

Like Asia, North Africa still has a summer monsoon. But now it's weak and only brings rain many thousands of kilometres to the west and south of here. But 8000 years ago, monsoon rains fell over the whole of the Sahara including the Gilf Kebir. So what happened?

Update: After weeks in the Midwest the 23 Degrees team finally catch a tornado!

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Helen Czerski Helen Czerski | 16:30 PM, Tuesday, 21 June 2011

Distance travelled ~ 442'521'600 km: day 172

tornado, midwest US

The team were pleased late yesterday (June 20 2011) afternoon to finally catch sight of a tornado

Right at the end of our last day here, the wait finally paid off. We were driving in the convoy of radar trucks towards a storm system, which looked to us exactly the same as the others we'd seen, and a calm voice on the radio said "tornado at 1 o'clock". We drove up and over a slight hill and suddenly the grey sky in front of us resolved itself into an enormous dark tower, moving sideways across the road in front of us. It was probably a mile or so away, and we were all overwhelmed by just how massive it was. The photos don't do justice to the scale of it. We hopped out of the car and started filming, but after only 3 or 4 minutes, the tornado started to shrink, and had soon vanished. It had looked so solid and substantial, but what we were looking at was just the low-pressure core of the rotating storm. When the pressure drops enough, the moisture in the air will condense and so a tornado is a part of the cloud reaching down to the ground. But if the pressure rises just slightly, all that water will evaporate again, and that huge structure will vanish. And so our tornado evaporated, and the core became invisible again.

We drove down the road, to the place where the tornado had crossed it. There were ploughed fields on either side, and you could see the churned up soil where the tornado had passed across one field, across the road, through the field on the other side and over to a cluster of trees about half a mile away. We looked at a couple of trees next to the road, a short distance from the track. 15 minutes before, these had been healthy trees, but now they were ripped apart, and there was a really strong smell of sap to remind us how recently they'd been shredded.

There was no doubt in any of our minds that it had been worth the wait, and we felt very lucky to have been there for the short time the tornado had touched down. Seeing the destruction was sobering, and it brought home how much energy is swirling around in the atmosphere above us. A tornado is a reminder of how our atmosphere can be simmering away and still be almost completely invisible, until a threshold is crossed and a really destructive storm results.

Midwest USA update: what is it like to chase tornadoes?

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Helen Czerski Helen Czerski | 15:00 PM, Tuesday, 21 June 2011

Distance travelled ~ 442'521'600 km: day 172

(Helen Czerski and some of the 23 Degrees team stayed back in Midwest USA to continue tracking tornadoes whilst the others moved on to the next stop in Egypt to film the Summer solstice. Here is Helen's update from yesterdays chase).

supercell midwest USA

20 June 2011, DOW stopped to scan the sky

If you stand outside in the Midwest, half of everything that you can see is sky. It's easy to see why everyone here is interested in storms - the land is completely flat and open, and you can watch these huge structures in the sky changing and growing from miles away. The rain, lightning, hail, the sudden darkness and the occasional unexpected rainbows are awe-inspiring. By comparison, a human being is tiny, slow and vulnerable.

The process of finding the eye of the storm is less awe-inspiring. The reality of storm-chasing involves patience more often than it requires adrenaline. As I write this, we're waiting with the storm scientists while they decide where we're going today. There are ten scientists and students with laptops, all looking at the current radar data and weather forecasts, discussing whether different wind conditions are more or less likely to combine to produce supercells, and also just waiting to see how the weather changes as the day goes on. Storms tend to develop later in the day, because that's when the ground and air have heated up enough to start building storm cells. So, we have to wait for the complexities of the atmosphere to call the shots. This is why these scientists are out here - the more they understand about tornado formation, the better the forecasts will be. And it won't just be scientists and tv crews that will benefit, but the people whose homes and businesses might get hit.

storm over midwest USA, 19 June 2011

20 June 2011, storm that came closest to dropping a tornado

When the storms do start to develop, the pace changes dramatically. The hunt is on. The radar trucks stop every few minutes to scan the sky in detail. You're right underneath a huge black cloud, and it's moving and changing as you watch it. You drive through heavy rain, hail and really strong winds to get ahead of the storm , and all the time it's above you, metamorphosing, with huge blocks of cloud ploughing through the sky below the main storm cloud. You can see the lower clouds rotating around you. And this was the point yesterday when I finally really understood why people spend so much time trying to see tornadoes. I stepped out of our car, and the speed with which the low clouds were spinning around me was stunning. I could see them rotating around a half-mile wide circle almost as if they were gathering themselves together, and the whole thing was huge and incredibly energetic. It was hard not to think of it as alive, because it was so dynamic. Being right underneath such a piece of atmospheric architecture was genuinely awe-inspiring, and definitely worth the wait. And this one wasn't even a tornado, just a mesocyclone, which is the stage before a tornado.

All this is generated by simple physical processes, operating on a huge scale. Most of the time they're invisible, but when they're all concentrated in once place like this so you can see them, it brings home the scale and power of what's going on around us all the time.

The scientists are getting up, and a decision about where to go has been made. Today is our last chance to see a proper tornado, and it all depends on whether the huge forces in the atmosphere cooperate. All we can do is follow behind and admire.

It's Summer Solstice and we head to Aswan Egypt, just like Eratosthanes

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Stephen Marsh Stephen Marsh | 10:30 AM, Tuesday, 21 June 2011

Distance travelled ~ 442'521'600 km: day 172

Today Kate Humble and some of the 23 Degrees team are in Aswan, Egypt. They are there to reveal something fascinating about the Summer Solstice and the tilt of our planet.

The Earth's tilt reveals itself every time we step out in the Sun but none more so than today on the solstice. The angle between the Sun and the Earth was first worked out over 2000 years ago. It was a discovery made near the city of Aswan, at the bottom of an ancient well by a Greek scientist and philosopher, Eratosthanes.

Eratosthanes was a poet, an athlete and a true polymath. He invented the word geography and even created a map of the world. He tried to write a chronology of world history and he invented the leap day. He also proposed a simple algorithm to work out prime numbers and all the time he was the head librarian of the library at Alexandria, the greatest treasure trove of knowledge of its time.

The story goes that 250 BCE on the summer solstice Eratosthanes was in Aswan and at midday, he looked down to the bottom of a well and saw his reflection staring back at him. Now as with most geniuses he noticed something that the rest of us would have missed. Something that told him about the very nature of our relationship with the sun.

When Eratosthanes looked at his reflection in the water in the well, he noticed he threw no shadow because the Sun was directly overhead. Now to most people that wouldn't have meant much but for Eratosthames it was an important revelation. Let me explain. Eratosthames didn't live here in Aswan, he lived 500 miles north in Alexandra. You might ask why that's significant. Well history has it that he noticed that when he was in Alexandria at the same time, on the Summer solstice on a previous year he did cast a small shadow. In fact he'd measured its length and angle.

So when he saw there was no shadow in Aswan he realised that at the very same moment, midday on the solstice, the Sun's position in the sky was different in Alexandra to Aswan. So, by calculating the angle of the shadow he cast in Alexandria, and its distance to the well here, Eratosthenes was able to estimate the circumference of the earth with an astonishing 98% accuracy. And using the same data, he was able to establish the tilt of the Earth's axis, obtaining a value of 23° 51' 15". A pretty amazing result without GPS and modern computing methods.

From watching the position of the Sun, Eratosthanes observed something else. After June 21, shadows appear here once again at noon, and over the coming days, they lengthen. So this day and this place marks the most northerly apparent position of the Sun due to that 23 ½ degree tilt. But tracing a line of latitude, west to east, across the planet one can see the same thing. Aswan sits just above a hypothetical line of latitude, a line we know as the Tropic of Cancer. A line that circles the world at 23.4 degrees above the equator.

The northward drift of the Sun in our sky that begun at the Spring Equinox on March 21 ends now on the Summer Solstice. From this day on, in the northern hemisphere, the hours of daylight will start to reduce and the Sun will track a lower arc in the sky.

Kate and the team are visiting a well reputed to be the very same well that Eratosthanes looked down all those years ago, to tell the story of this remarkable man and his discovery about the tilt of our planet.

Can you calculate the tilt of the Earth?

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Aira Idris Aira Idris | 15:30 PM, Thursday, 16 June 2011

Distance travelled ~ 429'657'600 km: day 167 

In this blog post we are going to show you how you can calculate the exact tilt of Planet Earth by using your shadow. You can only do this at a certain time of the year, the Summer Solstice, and that moment is fast approaching.  

This year Summer solstice is on 21 June. This is the longest day of the year and also for us here in the northern hemisphere, the time when the Sun is highest in the sky. Astronomers regard it as the start of summer for the northern hemisphere winter for the southern.

So what's the Summer Solstice got to do with measuring the tilt of the Earth, I hear you ask. Well, the orientation of the Earth to the Sun is defined by angles, and on June 21 the physics align so that you can use the position of the Sun in the sky at 1pm BST to accurately measure the tilt of the Earth. It still works around 2 days before and 2 days after so you have a few days to try this out.

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Here's a tip - measure from the balls of your feet to the top of your shadow and remember be careful and don't look directly into the Sun.

The first important angle is Solar Zenith. This is the angle between the Sun and straight up and it's marked in green on the figure below. We can find this because the smaller this angle is - or the higher in the sky the Sun is - then the smaller your shadow. To work this out we use tan. If you know about tan, then your height is the adjacent side and your shadow is the opposite side of a square-angled triangle.

Geometry of Summer Solstice

Figure 1.

Next we need latitude. This is essentially the angle between the equator and your position on the Earth. You can see from the figure above that if you take the green angles away from the pink angle then you get the yellow angle. This angle between the equator and the place on Earth where the Sun is straight above you is called the "solar declination". But on the solstice it's exactly the same as the tilt of the Earth - convenient.

How to find your latitude?
There are loads of ways of getting your lattitude -a gps device maybe on your phone or satnav, or endless websites can provide you with this. Some are as simple as putting in your postcode.

Most importantly the 23 Degrees team would love to hear how you get on. Send us your calculations, photos or videos of you doing the challenge on the Solstice, or maybe a photo of your shadow. Shadows have long been a key indicator to our Earth's position in it's orbit around the Sun.

Continue the conversation and put #solstice in your tweets!

In pictures: A close one! water spout spinning towards ship, Croatia

Aira Idris Aira Idris | 11:15 AM, Thursday, 16 June 2011

Distance travelled ~ 429'657'600 km: day 167



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Daniel Pavlivonic sent in these amazing shots of Waterspouts during a storm in Dubrovnik, Croatia 21 June 2010. The Waterspout came from the left, and the ship went a little behind it, says Daniel, luckily missing a possibly deadly situation.

 If you capture images or video of weather phenomena and would like us to feature it as a story on our blog, email the 23 Degrees team





Sun-Earth-Moon relationship: First total lunar eclipse of 2011

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Aira Idris Aira Idris | 13:15 PM, Tuesday, 14 June 2011

Distance travelled ~ 424'512'000 km: day 165

One of the few significant things Earth and the Moon share is their relationship with the Sun. To an observer on Earth at least - as different portions of both the Earth and Moon's surfaces are illuminated, this signifies the movement of time and the root of our calendar, which is very important.

On 15th/16th June we will observe a unique point in the Sun-Earth-Moon annual relationship - a total lunar eclipse and the first for this year.

total lunar eclipse 2000

Image courtesy of Fred Espenak/NASA

It takes the Moon 27 1/3 days to orbit the Earth (lunar month 29 ½ days), going through the new Moon, first quarter, full Moon, last quarter and back to new Moon. A total lunar eclipse happens when there's a full Moon and the Moon passes through a part of the Earth's shadow, known as the umbra - an area not directly receiving the Sun's rays.

Although there is a full Moon every month, we don't get a total lunar eclipse each month because the Moon's orbit is not in the same plane as the Earth's around the Sun (the ecliptic). From the image below we can see that the Moon's orbit goes over and under the Earth's orbital plane around the Sun.

geometry of a lunar eclipse

Image courtesy Wikimedia commons

The inclination of the Moon's orbit is around 5 degrees to the Earth's orbit, and passes through the ecliptic only twice a month at a pair of points called the ascending and descending nodes. This is where the Nodal Axis is aligned with, or pointing at, the Sun.

The period when the Earth completely blocks the Sun's rays from the Moon is when we experience a total lunar eclipse - known as totality. This moment repeats itself every 6 months.

For this week's eclipse the best placed observers to see it in it's entirety are those in East Africa, central Asia, Middle East and West Australia, lasting a total of 1 hour and 6 minutes. For Europe and South America we will miss the beginning of the show and places like west Australia will miss the end - check specific times for your location. North America completely misses the total lunar eclipse.

Penumbral Eclipse Begins: 17:24:34 UT
Partial Eclipse Begins: 18:22:56 UT
Total Eclipse Begins: 19:22:30 UT
Greatest Eclipse: 20:12:37 UT
Total Eclipse Ends: 21:02:42 UT
Partial Eclipse Ends: 22:02:15 UT
Penumbral Eclipse Ends: 23:00:45 UT

(credit NASA)

What can you expect to see? The shade of the Moon at eclipse is hard to predict because of the Earth's atmosphere. Although the Earth will block out the Sun during totality, the Sun's rays will still penetrate through the Earth, and mixed with the dust and cloud in the atmosphere the total lunar eclipse may take a variation of different shades. Volcanic ash can also affect the shade of the total lunar eclipse - turning it a darker shade of red. Ash from the recent eruption of the Puyehue volcano in Chile may have placed some sulphur dioxide into the stratosphere, according to atmospheric scientist Richard Keen of the University of Colorado.

If you plan on observing or photographing the total lunar eclipse of June 15th/16th and would like to share your comments and images with the 23 Degrees team for a possible story or image gallery do get in touch.

The next long lunar eclipse will be in 2018.

Whilst Aurora watch is put on standby enjoy the NASA [VIDEO] of massive Solar Prominence 7th June

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Aira Idris Aira Idris | 16:30 PM, Friday, 10 June 2011

d ~ 414'220'800 km: day 161

According to NOAA there is still a 20% to 30% chance of spotting the Aurora Borealis within the next few hours. The massive Coronal Mass Ejection of 7th June didn't produce solar winds that reached Earth yesterday as originally predicted, but high latitude skywatchers have been told to remain alert - according to spaceweather

In case you missed it, here's the amazing video from NASA:

Back on the road and heading to Tornado Alley with Dr. Joshua Wurman

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Stephen Marsh Stephen Marsh | 11:00 AM, Wednesday, 8 June 2011

d ~ 409'075'200 km: day 159

It's early June and the 23 degrees team are back on the road capturing some of the planets' most exciting weather phenomena.

This time Helen Czerski and the team are in the Midwest of the USA tracking one of the deadliest weather events of them all. The Tornado.

They are starting off in Boulder Colorado with renowned Tornado expert Josh Wurman from the Centre for Severe Weather Research and heading out onto the Great Plains in pursuit of this elusive beast. It's elusive because tornadoes are notoriously difficult to film. You might find that surprising when there have been so many of these deadly twisters this season. The problem is it's very hard to predict where they will form and touch down on the ground. Using radar tornado experts can track the formation of thunderstorms from which a tornado can develop, but they can't predict when or if a thunderstorm will spawn the deadly twister.

Filming Tornadoes can also be dangerous. We've seen the horrific images of towns devastated by tornadoes in Alabama, and Missouri. They had little warning and the violent winds trashed everything in their path. That's why we are working with expert Josh Wurman, he's a veteran in tracking, studying and filming tornadoes. He's not just there to take us to where the storms might be forming; he's there to warn us if we are getting too close.

We are travelling in his custom-built mobile radar station weather laboratory called a Doppler on Wheels or DOW. Its packed with the latest detection gadgetry including Doppler radar that can track the developing clouds high up in the atmosphere. So far these vehicles have observed 141 Tornadoes and intercepted the eye of 11 hurricanes.

The team are going to be spending a few days out in what's known as Tornado Alley tracking these incredible weather systems to learn what are the conditions that transform air masses into these violent storms. We await they footage with great anticipation. Lets hope they get lucky and see a twister first hand.

23 Degrees photo of the day: Partial eclipse of midnight Sun

Aira Idris Aira Idris | 16:45 PM, Thursday, 2 June 2011

d ~ 393'638'400 km: day 153 of Earth's orbit

Partial Solar Eclipse 2011

Image captured last night by Oliver Lemke in Sweden.

An eclipse that occurs at midnight means that we are observing it across the North Pole and the top of the World. The next eclipse of 2011 will be the total lunar eclipse on June 15th, the first total eclipse of the year.

Tonight brings a rare eclipse of the Midnight Sun

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Aira Idris Aira Idris | 17:20 PM, Wednesday, 1 June 2011

d ~ 391'065'600 km: day 152 of Earth's orbit

Tonight brings a rare sighting for those lucky enough to live in the arctic - a partial eclipse of the midnight Sun. The partial eclipse we experienced on January 4th 2011 saw the moon pass between the Sun and the Earth, partially covering the Sun's view. Tonights partial eclipse however is special because it will be of the midnight Sun. As strange as it sounds there will be a partial eclipse of the Sun at night.

The Midnight Sun starts in March over the north pole and has its southern most extent on June 21st at the edge of the arctic circle. When either hemisphere is tilted directly towards the sun, the most polar regions are illuminated 24 hours a day, and viewed from Earth the sun is in the sky all day and all night.

For us in the UK we'll not see this eclipse, but sky watchers in places like northern Norway, Sweden, Finland, Siberia, northern China, remote parts of Alaska and Canada, and Iceland are in for a treat. The eclipse begins at sunrise in Siberia and northern China where the penumbral shadow first touches Earth at 19:25:18 UT. Two hours later, greatest eclipse occurs at 21:16:11 UT according to Fred Espenak of the NASA Goddard Space Flight Center.

"At this time of year the Sun doesn't set in Arctic parts of the world, so a solar eclipse is theoretically possible at all hours of the day" says Fred Espenak. He goes on to add that "when the clock strikes local midnight in northern Norway at the end of June 1st, about half of the lingering sun will be covered by the Moon."

map of the June 1st eclipse

Image © NASA/GSFC (full image here)

If you happen to spot this then add it to our photography pool. For information on the times that the partial eclipse of the midnight Sun will occur take a look at NASA's timetable.

And for those who don't want to miss out on this occasion -
Knut Joergen Roed Oedegaard, an astrophysicist at the Norwegian Centre for Science Education in Oslo will attempt to bring this to us via online automatic photo updates (as part of a project which focusses on the spectacular celestial events 2010-2015).

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