SDO solar observatory launches from Cape Canaveral
By Jonathan Amos
Science correspondent, BBC News
The Solar Dynamics Observatory launches in Florida
The US space agency Nasa has launched its Solar Dynamics Observatory (SDO) from Cape Canaveral in Florida.
It was the second lift-off attempt for the mission after Wednesday's effort was postponed due to high winds.
The observatory is designed to acquire detailed images of our star to explain variation in its activity.
An active Sun can disrupt satellite, communication and power systems on Earth - especially when it billows charged particles in our direction.
Scientists want to see if they can forecast this "space weather" better.
It is going to revolutionise our view of the Sun
Lika Guhathakurta, Nasa SDO programme scientist
The Atlas V carrying SDO left Earth at 1023 local time (1523 GMT). Its flight to separation of the spacecraft in orbit lasted almost two hours.
Once ejected from the rocket's Centaur upper-stage, SDO immediately deployed its solar panels to charge its batteries and start operating its systems.
"They're power-positive so all those things they wanted to do in those first few minutes have gone like clockwork," said Nasa launch director Omar Baez.
The Solar Dynamics Observatory will investigate the physics at work inside, on the surface and in the atmosphere of the Sun.
"SDO is the solar variability mission," said Lika Guhathakurta, the SDO programme scientist at Nasa Headquarters.
"It is going to revolutionise our view of the Sun and it will reveal how solar activity affects our planet, and help us anticipate what lies ahead.
"It will observe the Sun faster, deeper and in greater detail than any previous observations, breaking barriers of time, scale and clarity that have long blocked progress in solar physics."
With the launch under our belts we look forward now to the first images from SDO - showing the complex solar atmosphere in unprecedented detail
Richard Harrison Rutherford Appleton Laboratory
SDO's instruments will return images with a resolution 10 times better than the average high-definition television camera, and those pictures will come back at a rapid rate, every few seconds.
The mission will try to unravel the factors that drive the Sun's cycles of activity.
A key goal will be to probe the inner workings of the solar dynamo, the deep network of plasma currents that generates the Sun's tangled and sometimes explosive magnetic field.
It is the dynamo that ultimately lies behind all forms of solar activity, from the solar flares that explode in the Sun's atmosphere to the relatively cool patches, or sunspots, that pock the solar disc and wander across its surface for days or even weeks.
SDO is being launched at an opportune moment. Recent years have witnessed a very quiet star and the spacecraft will be able to monitor the Sun as it stirs into life.
"The Sun has been dramatically inactive," commented Richard Harrison, a co-investigator on SDO from the UK's Rutherford Appleton Laboratory.
"The last two years has had more than 250 days of no sunspots whatsoever.
"We believe this minimum is coming to an end; all the signals are there. We are seeing new active regions. They actually start at the higher latitudes in the Sun's atmosphere. Sunspots are forming; we're seeing the first big solar flares."
Solar activity varies greatly year on year (Footage: Nasa/Esa/Soho)
The UK is playing a prominent role in the mission, having supplied critical equipment for the SDO's instruments.
Professor Harrison explained: "The UK has played an important part in the scientific investment and planning for this mission, and we have supplied the CCD-based camera systems for two of the major instruments aboard SDO.
"With the launch under our belts we look forward now to the first images from SDO - showing the complex solar atmosphere in unprecedented detail."
The $850m (£545m) Solar Dynamics Observatory will study the Sun from a geosynchronous orbit above the Earth, and will operate for at least five years.
Its three remote sensing instruments are:
Helioseismic and Magnetic Imager (HMI): will study the motions and magnetic fields at the Sun's surface, or photosphere, to determine what is happening inside the star. It will try to decipher the physics of the solar dynamo - the very source of the Sun's activity. The dynamo regulates all forms of solar activity from the lightning-fast eruptions of solar flares to the slow decadal undulations of the sunspot cycle.
Atmospheric Imaging Assembly (AIA): is a suite of four telescopes that will image the corona, the outer layer of the Sun's atmosphere. The AIA filters cover 10 different wavelength bands, or colours, from the extreme ultraviolet to the visible. It will see details as small as 725km across. These images will be acquired every 10 seconds. Previous observatories have taken pictures at best every few minutes.
Extreme Ultraviolet Variability Experiment (EVE): will measure the Sun's energy output in extreme-ultraviolet (E-UV) wavelengths (this is called irradiance) with unprecedented precision. The Sun is at its most variable in the E-UV. E-UV rays can break apart atoms and molecules in the Earth's upper-atmosphere, creating a layer of ions that can severely disturb radio signals.
The UK is involved through the Rutherford Appleton Laboratory in Didcot; the e2v company in Chelmsford which made CCD camera detectors; the Mullard Space Science Laboratory in London; the University of Warwick; the University of Sheffield; and the University of Central Lancashire in Preston .
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