## Day 365: We're on our way back out again

| 15:00 PM, Saturday, 31 December 2011

(Phil Plait is an Astronomer and Author who writes the Bad Astronomy blog for Discover Magazine. His blog is dedicated to clearing up public misconceptions about astronomy and space science in the media. After working for ten years with the Hubble Space Telescope team at NASA Goddard Space Flight Center he went on to work on astronomy education. Phil has appeared on numerous TV and online astronomy features. Here Phil celebrates Perihelion which is just a few days away, and the point when 23 Degrees started it's project a year ago. Phil can be reached @badastronomer)

Distance travelled ~ 938'107'200 km

The Earth travels 'round the Sun at the terrifying speed of 30 kilometers per second, making a gigantic circle nearly a billion kilometers in circumference once per year.

That's a fantastic distance, but in one way it's a bit disappointing. After all, a year after you started this high-velocity trip, you're back where you started.

However, the journey isn't actually a perfect circle. It's off by a tiny amount, so slight that you'd never notice if someone didn't tell you. But in fact, this minor deviation can make a big difference: it means that the Earth's distance from the Sun changes over its orbit to the tune of over 5 million kilometers!

That difference amounts to about 3.4% of the average distance to the Sun, which astronomers, for convenience, call an Astronomical Unit, or AU. In real terms, an AU is 149,597,870 km plus a bit. When the Earth is at aphelion - its farthest point from the Sun - it's about 152,141,000 kilometers from our star. At perihelion, that distance shrinks to 147,055,000 kilometers.

Aphelion occurs on one side of the Earth's orbit, and perihelion on the other. It takes the Earth half a year to travel that distance, of course, so in a sense it drops toward the Sun by 5 million kilometers in about 182.5 days - an average velocity of well over 1100 km/hr.

And my teachers told me I'd never go anywhere.

You might expect this change in distance to the Sun would have an effect on the Earth's temperature. It does, in fact, but it's pretty small, only a couple of degrees Celsius. That's swamped by the seasonal change in temperature due to the Earth's tilt, which is what really drives the seasons. Think of it this way: the Earth reaches perihelion in January, which is the dead of winter for the northern hemisphere. While this does make northern winters a tad more clement, the amount is too small to make an appreciable difference.

Oddly, for those in the antipodes of the southern hemisphere, we're closest to the Sun in their summer. You'd expect temperatures then to be higher than average, but in reality they're about the same as their boreal neighbors. Why is that? It's because the southern hemisphere is dominated by the Pacific Ocean, and water is an excellent heat sink. It absorbs the extra heat in the summer, and releases it in the winter, mitigating temperature extremes.

Weather, it turns out, is complicated.

There is one measurable effect, though: the size of the Sun changes by that same 3.4% over the course of half a year. You'd never suspect that by eye - of course, looking at the Sun is not a suggested pastime - but if you carefully take pictures of it over the course of the year you'll see it, as astronomer Anthony Ayiomamitis did in the picture here. Since the change is slow day-by-day it's beneath our notice, but the telescope doesn't lie.

So when is the next perihelion? Why, it's January 5, 2012, and it will occur at about 01:00 GMT. At that moment, or thereabouts, the Earth will again be as close to the Sun as it will get all through 2012. The 23 Degrees project started on the day of Perihelion for 2011 and we're already on our way back out, and on July 5, at 04:00 GMT, the Earth will reach the apex of its orbit, and oh so slowly start the fall back toward the Sun.

And it will do this, over and over for the next few billion years, until the Sun swells into a red giant and cooks the Earth like a banger in a blowtorch.

So enjoy the ride while you can.

## Why are clear nights so cold?

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| 15:00 PM, Wednesday, 9 November 2011

Distance travelled ~ 804'321'600 km

It's the season for baked potatoes, parkin, treacle toffee and bundling up to stay warm. I love the sharp, cold starry evenings and being able to see my breath - it's not every day that you get to make your own cloud! But in the past few days I've remembered that there's a price to pay for being outside on those fabulous clear evenings. It's cold. Frigid, frosty, freezing. Your knuckles go red and the inside of your nose feels like it's full of ice. Why can't we admire the autumn stars in comfort?

The answer is to do with how energy gets from place to place, and how much clouds get in the way. We may associate clouds with bad weather, but when it comes to nighttime, clouds are our friends.

Image credit NASA

Our planet's energy comes from the Sun, mostly as visible light. We know that - it lights up our world. Air is invisible, and by definition visible light travels straight through it. So on the way in, the Sun's energy is carried by all the colours of the rainbow, straight through the atmosphere and all the way to the ground. The ground absorbs that energy and warms up. Black tarmac absorbs more heat than white sand, but they all capture some.

Next time you make some toast, watch the element in your toaster. As it gets hotter, it glows, first dull red, then bright red and then orange and yellow. Hot things give away their energy by glowing - it's a fundamental rule of physics - and the colour tells you their temperature. The ground under our feet, along with you and everything else around you also glows. But because those things aren't as hot as your toaster, they glow in the infrared, which we can't see directly.

So the ground glows in the infrared all day and all night, constantly emitting invisible energy back upwards. Some of this energy heats the air near the ground, but some keeps going upwards. And here's where clouds matter at night. Clouds are really good at capturing that infrared radiation and sending it back down the Earth. They act like a blanket, trapping heat between the ground and the clouds. If there are no clouds, the energy from the ground just goes up, up, and away...

Whenever it's a clear night and you can see lots of stars, there is nothing to trap all that infrared energy, so it's lost to space and we feel cold. If it's cloudy, there are no stars to see, but we have a nice warm blanket above us, keeping the heat in. The fact that Earth gains energy as visible light and loses it as infrared light is really important for the heat budget of our planet, not just for freezing astronomers.

Sadly, this means that stargazing will always require extra layers. Happily, that means extra excuses in life for hot chocolate. In fact, just writing this has made me feel chilly. It might be hot chocolate time right now!

## Keeping track of time

| 18:00 PM, Friday, 28 October 2011

Distance travelled ~ 773'769'600 km

Noon is personal. It's the time of day when the sun is highest in the sky and your shadow is shortest. It's the reference point for a clock that is always with you, because you can be your own sundial. The spinning Earth provides us with a built-in natural chronometer. Brilliant!

That clock has served nature well for millennia - birds sing at dawn, foxes come out at dusk, humans go to sleep when it gets dark, and we all live day to day. One daily cycle follows another. But the growth of human civilizations and the need for greater co-operation than ever before meant that humans had to control time instead of being controlled by it. Clocks were standardized. The day was split up into hours, and humans had to agree to start work, meet or provide services at specific times. It was the only way of co-ordinating a civilization. But the Sun was still the reference point.

Faster travel, and inventions like the radio and telephones, meant that time zones had to be invented. Local noon where I am, in Southampton, happens four minutes later than local noon in London, so society agreed that all of the UK would be in a single time zone, for convenience. 12 o'clock in Southampton now happens at the same time as 12 o'clock in London. The Sun is no longer the reference point. The shortest shadows still happen around lunchtime, but you can't set your watch by that any more. And as clocks got more and more accurate, we discovered that the shape of Earth's orbit means that the length of a day varies by about a minute over the course of each year. Solar time seemed to be almost unhelpful in our standardized world.

So humans weren't living and working according to the Sun any more, but sunlight hadn't gone away.

The standardization of time meant that some people were sleeping when it was light and working when it was dark. And so Daylight Savings Time was invented, to try and compensate for the limitations imposed by standard time. The clocks go back in the UK Sunday 30 October 02:00am in a return to GMT, after a summer of allowing us an extra hour of daylight in the evenings (upcoming DST times). Of course, we don't actually get an extra hour of daylight - we just move our time reference to take that hour off the start of the day and tack it on the end. We couldn't have built the modern world without standardized time, and now we're trying to patch up some of its inconveniences.

Image courtesy of C.G.P Grey. For more on daylight saving watch his video.

Should we bother? Every clock change causes sleep deprivation, a demonstrated drop in productivity and a day where the whole country risks turning up at the wrong time. It's a nice ritual to mark the changing of the seasons, but is it worth it?

I think that the crux of the argument might be in how society is changing. Fifty years ago, a giant siren marked the time when work began and ended in factories. The development of our society relied on us all working together, at the same time. It was an enormous example of human co-operation. But now, we live less constrained lives. We work flexibly, and internationally. The standardization of the working day is disappearing - some businesses start work at 8am, some at 10am. I adapt my daily routine so that I can go running when it's light, whether that's in the morning or the evening.

As long as I get my work done, maybe it doesn't matter when I do it. So I can choose for myself what I do with my daylight hours, irrespective of the official time that they start and end.

Do we even need time zones any more? Maybe the logical end to this argument is that we could have just one Earth time, so that everyone has lunch at a different official time, but it's still when the sun is more or less overhead. I'm not necessarily advocating for that, but it's not as close to science fiction as you might think. Scientists in every country frequently record data using "Universal Time" or Zulu time, which is GMT. That way there's no confusion at all over when it was recorded, wherever you were on the planet.

So, is the era of British Summer Time/Daylight saving time over? What do you think?

## How likely is 2013's 'perfect solar storm'?

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| 11:30 AM, Tuesday, 23 August 2011

Distance travelled ~ 603'268'000 km

(Lucie Green is a solar researcher based at the Mullard Space Science Laboratory, UCL's Department of Space and Climate Physics. She studies activity in the atmosphere of our nearest star, the Sun, with particular focus at immense magnetic fields in the Sun's atmosphere. Lucie is also a Science writer and has been involved in a variety of Science programmes such as Sky at night and recently Radio 4's programme the infinite Monkey cage.)

It seems that barely a week goes by at the moment without the Sun being in the news, for seemingly contradictory reasons. One minute we are being told that the Sun is going to cause a global disaster as the result of super-sized solar activity, the next that Sun is going into hibernation. So, what exactly is going on?

Courtesy of SOHO/EIT consortium. SOHO is a project of international cooperation between ESA and NASA

The Sun has a cycle in which its magnetic field pulses in size and complexity roughly every 11 years. Coronal mass ejections (CMEs), huge bubbles of magnetic field containing charged particles, are a natural part of this cycle. At the moment we are approaching solar maximum (expected to occur around 2013) which means that the number of ejections is on the rise and so too are some worrying consequences here on Earth.

CMEs can inject charged particles into the Earth's magnetic field which, if accelerated, lead to the beautiful aurora. The flipside is that these particles can also damage our satellites, lead to satellite failure and produce currents in our power lines causing problems for national power grids. Most notably, in 1989 a transformer in the Canadian national grid failed due to such currents and several million people lost their electricity for over nine hours. So, the increasing number of CMEs is good news for people wishing to view the aurora but bad news for our space-based and electrical infrastructure.

Some news articles are predicting that in 2013 the perfect solar eruption will occur that will cause a global disaster through the simultaneous failure of electricity networks all over the world and the loss of the satellites that modern society relies on for communication, navigation and banking. However, many aspects need to come together to produce this 'perfect solar storm' which makes such an event hard to forecast. This scenario isn't pure fiction though.

The reasoning is based on studying previous events, in particular a solar eruption that occurred in 1859 which produced such a strong display of the aurora that they were seen down toward the equator. If this event repeated itself today it is likely that the worldwide damage caused would cost a trillion dollars. [For more information on how coronal mass ejections affect us: NOAA/Space weather prediction center ]

No individual solar cycle is the same as the next though, and this brings me to another reason that the Sun has been in the news. The Sun has only recently come out of the deepest solar minimum for 100 years. Things have been very quiet on the Sun. So whilst some are worried that the Sun might cause global destruction, others are worried that the Sun is going to switch off. On the face of it these are contradictory stories but on closer inspection this is not so.

On the timescale of a few years solar activity and the number of CMEs is on the rise and we will experience more effects on our technology. However, on the timescale of decades, it looks like the magnetic cycle of our Sun may decline. This idea could be extrapolated to conclude that the Sun will switch off altogether but in reality there is an very small chance of this happening. Things may quieten down, but they will pick up again.

Ultimately, we are living in a gusty outflow of magnetic field and charged particles coming from the Sun. This has led to a new era of 'space weather' prediction where we are monitoring the near-Earth space environment to make sure we protect ourselves from the harmful effects of the Sun's emissions. Whatever level of activity the Sun decides to produce we will feel the consequences. Understanding and predicting the weather in space should be given a high priority.

## This week's space weather roundup and Saturn's northern storm

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| 16:00 PM, Tuesday, 12 July 2011

Distance travelled ~ 496'550'400 km

Day 193 on our circumnavigation of the Sun. Down on planet Earth it's been a rather boring start to July weather-wise, overcast, a bit humid a bit stormy. But in space it's been anything but dull.

July 5th NASA recorded the fiery death of an unnamed icy comet, which plunged into the Sun.

On July 6th NASA published some photos of a massive electrical storm on the planet Saturn that's been raging for months. The so-called Great White Spot is so massive it would cover half of the Earth and so violent those scientists have counted over ten lightening flashes a second. Such giant storms are relatively rare and only six have been witnessed in the last 135 years.

Then on July 7th a Coronal Hole opened up in the surface of the Sun. So what's a coronal hole. Well as we orbit the Sun we're bathed in essential warmth and energy, but we are also blasted by a blizzard of radioactive particles called the solar wind. This barrage is 24/7 but sometimes a hole opens up in the suns surface, a coronal hole, triggering the release of a really intense stream of solar wind. Normal solar wind travels at around 1,440,000 kilometres per hour but the wind blasting out of a coronal hole shoots out at up to 4,000,000kmph. These supercharged solar wind particles finally reached us two days later. Most were diverted by our magnetic shield but some hit the atmosphere and triggered auroras far south across the USA.

Today NASA released footage of some increased activity on the eastern region of the Sun. The Sun was hurling up huge amounts of material high above the stellar surface. You can see it yourself at spaceweather.com
As it happens this activity is not directed towards Earth, but NASA has detected a very active sunspot with the "oh so catchy" name 1247.

Image NASA/SDO

But don't let the unexciting name fool you, because it's anything but boring. It has a magnetic field with enough stored energy to create a M-Class solar flare, that's a pretty big explosion from the sun surface. Solar flares are classified according to their x-ray brightness. X-class flares are huge and can cause giant radiation storms and nation-wide radio blackouts. M-class flares are as the "M" suggests medium-sized and can trigger/cause small radio blackouts while C-class flares are small and have no effects on Earth.

NASA predicts there's a 10% chance of an eruption from the sunspot in the next 24 hours, and that one is directed towards Earth so watch this space.

Who said space is empty?

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