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‘Hubble for the Sun’ returns amazing first imagery
Posted: 22 April

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The Solar Dynamics Observatory (SDO), launched by NASA on 11 February, has produced its first pictures and movies, illustrating gigantic prominences, waves rippling across the the face of Sun that instigate coronal mass ejections, and the first measurements of solar flares in extreme ultraviolet, all in higher resolution than ever before.

A still from an SDO movie that shows a giant prominence being ‘belched’ from the Sun on 30 March. Image: NASA/GSFC.

“It’s a golden age for solar physics,” says Professor Richard Harrison of the Rutherford Appleton Laboratory, where the 16 megapixel camera systems for SDO’s Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI) instruments were developed in association with Chelmsford-based technology company e2v. Harrison is one of four British co-investigators on SDO, and highlights the mission’s role within the current fleet of spacecraft looking at the Sun. “There are other major missions like SOHO, STEREO and Hinode, and they are all different – SDO doesn’t replace anything – but at the same time they complement each other,” he tells Astronomy Now. “When combined they are a wonderful international fleet for figuring out how the Sun works and how it influences us.”

A multiwavelength ultraviolet image of the solar disc, also from 30 March, showing several prominences and active regions. The false colours indicate different temperatures, with red indicating temperatures of about 60,000 degrees Celsius, and blues and greens highlighting regions that are over a million degrees. Image: NASA.

However, because of its high-resolution imaging capabilities, SDO will surely make a splash in the public’s appreciation of the Sun on a level with the Hubble Space Telescope’s effect on our understanding of the wider Universe. This is evident in the clarity of the images recently released, in particular one movie that focuses on a looping prominence before pulling back to show a jaw-dropping view of the Sun’s entire disc.

SDO’s modus operandi is to examine the Sun’s magnetic field, and understand how it is generated, structured and ultimately drives the solar wind and the potentially dangerous mass ejections of plasma and radiation. To assist it during its five year mission, SDO carries three instruments, the aforementioned AIA and HMI, and also an Extreme Ultraviolet Variability Experiment, which will seek to understand how solar radiation and mass ejections affect Earth’s upper atmosphere when they buffet against it, heating the ionosphere, swelling the atmosphere and breaking down molecules. Meanwhile, the AIA is a collection of four telescopes that will observe the Sun at ten different wavelengths, while the HMI can probe the solar interior by watching for vibrations that ripple across the surface (the Sun’s photosphere), evident in the Doppler shifting of emission lines as the surface rises and falls.

“We are beginning to understand what the interior of the Sun is like by understanding how it is ‘ringing’,” says Harrison. “We’ve had some success over the years in predicting when sunspots will form by looking at the way the surface is vibrating using SOHO. Now we’re taking that to the next level with SDO, where it is a matter of recognising areas where magnetic fields are going to emerge and which might lead to eruptions.”

One of the challenges to be faced over the next five years is learning how to deal with the 1.5 terabytes of data that comes down from the spacecraft every day. “We’re used to megabytes, not terabytes,” says Harrison. Rather than scanning images by eye, solar physicists will instead employ powerful software to analyse the images. “There are now a few sites around the world where we are beginning to put together archives and pipelines where we will process the data. At the University of Central Lancashire they have set up a special facility run by Dr Robert Walsh that will do just that, and scientists in the UK will be able to go and get data from there.”

Can SDO answer the big questions, namely how is the solar wind generated, and how does the Sun’s magnetic field manifest itself, within its projected five year lifetime? “We very quickly get to the point where we realise that to get down to the fine detail to understand how magnetic fields form and evolve, and find out what causes disturbances, then we need the high-resolution imagery from SDO,” explains Harrison. “Combining SDO with the other missions puts us in a position to make great strides and to be able to understand a lot more about how the Sun works in a way we’ve not been able to in the past.”

-Solar prominence movie: WATCH
-Watch waves travel across the solar surface at different wavelengths, as they spark the eruption of a coronal mass ejection: WATCH
-A ‘Dopplergram’ for the surface of the Sun, showing vibrations that are incurred from disturbances in the interior of the Sun: WATCH