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The Sun as never seen before

FOR THE FIRST TIME in history, a stunning view of the whole Sun is visible to the world.

The unique 360-degree view of the Sun, unveiled today, comes from NASA’s two STEREO (Solar TErrestrial RElations Observatory) spacecraft, which were aligned exactly opposite each other on either side of the Sun.

The 360-degree coverage from STEREO is enhanced by NASA’s SDO mission (Solar Dynamics Observatory), which images the Sun in high resolution. As the STEREO probes continue flying to the far side of the Sun, the area of unseen solar territory on the near side will increase, and SDO’s cameras will play a vital role in filling the gap.

Working together, these new views of the Sun will allow scientists to better predict space weather and the violent eruptions from the Sun’s surface. These can damage satellites, disrupt communications and disable power systems on Earth.

“For the first time ever, we can watch solar activity in its full 3-dimensional glory,” says Angelos Vourlidas, a member of the STEREO science team at the Naval Research Laboratory in Washington, DC.

“This is a big moment in solar physics,” says Vourlidas. “STEREO has revealed the Sun as it really is–a sphere of hot plasma and intricately woven magnetic fields.”

Now we know what’s coming

Each STEREO probe photographs half of the star and beams the images to Earth. Researchers combine the two views to create a sphere.

These aren’t just regular pictures, however. STEREO’s telescopes are tuned to four wavelengths of extreme ultraviolet radiation selected to trace key aspects of solar activity such as flares, tsunamis and magnetic filaments. Nothing escapes their attention.

“With data like these, we can fly around the Sun to see what’s happening over the horizon—without ever leaving our desks,” says STEREO program scientist Lika Guhathakurta at NASA headquarters. “I expect great advances in theoretical solar physics and space weather forecasting.”

Sun as seen by STEREO and SDO

The solar sphere as seen by STEREO and the Solar Dynamics Observatory on January 31, 2011.

Consider the following: In the past, an active sunspot could emerge on the far side of the Sun completely hidden from Earth. Then, the Sun’s rotation could turn that region toward our planet, spitting flares and clouds of plasma, with little warning.

“Not anymore,” says Bill Murtagh, a senior forecaster at NOAA’s Space Weather Prediction Centre in Boulder, Colorado. “Farside active regions can no longer take us by surprise. Thanks to STEREO, we know they’re coming.”

Insight into the Sun

“The Sun is a truly complex object which influences many aspects of our lives,” said Professor Richard Harrison, Principal Investigator for the UK-built instruments on STEREO and SDO Co-Investigator.

“In the same way that you would not expect to understand the workings of the brain by studying just a small part of it, a global investigation into the nature of our star as a complete object is essential to understanding how it works.”

“The STEREO mission has already shown us some wonderful sights, solar eruptions arriving at the Earth to comets struggling against the solar wind,” said Dr. Chris Davis, STFC STEREO Project Scientist.

Artist's concept of the STEREO spacecraft

An artist's concept of the twin STEREO spacecraft orbiting the Sun ahead of, and behind, the Earth. On February 6, the probes had separated along Earth's orbit enough so that they were on opposite sides of the Sun.

“I’m very excited about this new stage of the mission and am looking forward to many years of unique observations.”

Dr Davis is also a leading scientist in Solar Stormwatch, a project in which members of the public use images from STEREO to spot explosions on the Sun, track them across space to Earth and provide an early warning to astronauts.

Scientists have already established that the magnetic fields in the Sun’s atmosphere drive solar activity on a global scale. This view of the entire Sun will enable more detailed studies of these processes at work. The 360-degree observations will continue for the lifetime of the missions.

Solar missions

NASA has been building toward this moment since October 2006 when the STEREO probes left Earth, split up, and headed for positions on opposite sides of the Sun.

February 6, 2011, was the date of “opposition”—ie. when STEREO-A and -B were 180 degrees apart, each looking down on different solar hemispheres. NASA’s Earth-orbiting Solar Dynamics Observatory is also monitoring the Sun 24/7. Working together, the STEREO-SDO fleet should be able to image the entire globe for the next 8 years.

The NASA STEREO mission was launched in October 2006 and is providing a totally new perspective on the Sun. The two identical spacecraft are offset from one another, one flying ahead of the Earth and the other behind. The spacecraft look back at the Sun and the space between the Sun and the Earth, which allows 3D images of the Sun to be produced.

Solar Dynamics Observatory (SDO) is the first mission in NASA’s Living with a Star (LWS) program and was launched in February 2010. SDO’s unique orbit allows high resolution images of the Sun to be recorded every three quarters of a second, providing in-depth information about the Sun’s complex magnetic fields and space weather generated by solar flares and violent eruptions (CME’s) from the Sun’s atmosphere which can disable satellites, disrupt communications, cause power grid failures, and expose astronauts to deadly particle doses.

Adapted from information issued by NASA / STFC.

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Aussie amateur spots Mercury’s tail

The planet Mercury

The planet Mercury. Astronomers have known that the planet has a tenuous gas tail stretching into space, but now an Australian amateur astronomer has spotted it in data from a Sun-monitoring satellite.

Scientists from Boston University’s Centre for Space Physics reported today that NASA satellites designed to view the escaping atmosphere of the Sun have also recorded evidence of escaping gas from the planet Mercury.

The STEREO mission has two satellites placed in the same orbit around the Sun that the Earth has, but at locations ahead and behind it. This configuration offers multi-directional views of the electrons and ions that make up the escaping solar wind.

Movie of Mercury's tail

This movie covers a 4-day period and shows Mercury's tail as seen by the STEREO A spacecraft on 6-9 February 2008. The faint tail can be seen streaming off to the top left of the planet.

On occasion, the planet Mercury appears in the field of view of one or both satellites. In addition to its appearance as a bright disc of reflected sunlight, a ‘tail’ of emission can be seen in some of the images.

Of special interest is the way the tail feature was spotted in the STEREO data. It was not found by the Boston University team, but by Dr Ian Musgrave, a medical researcher in Adelaide, South Australia, who has a strong interest in astronomy.

Viewing the on-line database of STEREO images and movies, Dr Musgrave recognised the tail and sent news of it to Boston asking the BU team to compare it with their observations.

“A joint study was started and now we have found several cases, with detections by both STEREO satellites,” explained Jeffrey Baumgardner, Senior Research Associate in the Centre for Space Physics at Boston University, and the designer of the optical instruments that discovered the exceptionally long sodium tail.

Schematic representation of the viewing geometry that allows the STEREO camera systems to make observations of Mercury’s tail

One of the twin STEREO spacecraft was in the right position to see the tail sweeping away from Mercury in a direction opposite to the Sun.

Tail blown by sunlight

This new method of observing Mercury and efforts to try to understand the nature of the gases that might make up this tail feature were topics presented at the European Planetary Science Congress meeting in Rome today.

It has been known that Mercury exhibits comet-like features, with a coma, or cloud, of tenuous gas surrounding the planet and a very long tail extending in the anti-sunward direction.

From Earth, observations of both of these features can be done using light from sodium gas sputtered off the surface of Mercury. The Sun’s radiation pressure then pushes many of the sodium atoms in the direction away from the Sun, creating a tail that extends many hundreds of times the physical size of Mercury.

“We have observed this extended sodium tail to great distances using our telescope at the McDonald Observatory in Texas,” Boston University graduate student Carl Schmidt explained, “and now the tail can also be seen from satellites near Earth.”

Much closer to Mercury, several smaller tails composed of other gases, both neutral and ionised, have been found by NASA’s MESSENGER satellite as it flew by Mercury in its long approach to entering into a stable orbit there.

Adapted from information issued by Europlanet / Boston University / NASA.

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