Light Bridges on the Sun

Credit: G. Scharmer, L. Rouppe van der Voort (KVA) et al., SVST

Explanation: Bridges the length of a planet can form on the Sun in a matter of hours. Known as light bridges, these structures may form as large sunspot groups decay. Above, one of the sharpest photographs of the Sunever taken shows two such light bridges that appeared late last month. The 5000-kilometer long bridges connect moderately dark penumbral regions across the cool abyss of two dark sunspot umbras. A movie shows that material tends more to rise from below and fall rather than to cross the light bridges. Bright bubbling granules surround the sunspot group. The impressive details on this recently released picture from the Swedish Solar Vacuum Telescope were made possible by new adaptive optics that correct for the blurring of the Earth’s atmosphere. What eventually became of the light bridges? As days progressed, the bridge region expanded to fill the void as the sunspots moved apart and decayed.

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)

Sungrazer

Credit: LASCO, SOHO Consortium, NRL, ESA, NASA

Explanation: Arcing toward a fiery fate, this Sungrazer comet was recorded by the SOHO spacecraft’s Large Angle Spectrometric COronagraph (LASCO) on Dec. 23rd, 1996. LASCO uses an occulting disk, partially visible at the lower right, to block out the otherwise overwhelming solar disk allowing it to image the inner 5 million miles of the relatively faint corona. The comet is seen as its coma enters the bright equatorial solar wind region (oriented vertically). Spots and blemishes on the image are background stars and camera streaks caused by charged particles. Positioned in space to continuously observe the Sun, SOHO has detected 7 sungrazing comets. Based on their orbits, they are believed to belong to a family of comets created by successive break ups from a single large parent comet which passed very near the sun in the twelfth century. The bright comet of 1965, Ikeya-Seki, was also a member of the Sungrazer family, coming within about 400,000 miles of the Sun’s surface. Passing so close to the Sun, Sungrazers are subjected to destructive tidal forces along with intense solar heat. This comet, known as SOHO 6, did not survive.

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)

A Green Flash from the Sun

Credit & Copyright: Juan Carlos Casado

Explanation: Many think it is just a myth. Others think it is true but its cause isn’t known. Adventurers pride themselves on having seen it. It’s a green flash from the Sun. The truth is the green flash does exist and its cause is well understood. Just as the setting Sun disappears completely from view, a last glimmer appears startlingly green. The effect is typically visible only from locations with a low, distant horizon, and lasts just a few seconds. Agreen flash is also visible for a rising Sun, but takes better timing to spot. A slight variant of this was caught in the above photograph, where much of the Sun was still visible, but the very top appeared momentarily green. TheSun itself does not turn partly green, the effect is caused by layers of the Earth’s atmosphere acting like a prism.

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)

A Wind From The Sun

Credit: SOHO Consortium, UVCS, EIT, ESA, NASA

Explanation: A wind from the Sun blows through our Solar System. The behaviour of comet tails as they flapped and waved in this interplanetary breeze gave astronomers the first hint of its existence. Streaming outward at 250-400 miles/second, electrons and ions boiling off the Sun’s incredibly hot but tenuous corona account for the Solar Wind – now known to affect the Earth and other planets along with voyaging spacecraft. Rooted in the Solar Magnetic Field, the structure of the corona is visible extending a million miles above the Sun’s surface in this composite image from the EIT and UVCS instruments onboard theSOHO spacecraft. The dark areas, known as coronal holes, represent the regions where the highest speed Solar Wind originates.

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)

Sun Storm: A Coronal Mass Ejection

Credit: SOHO Consortium, ESA, NASA

Explanation: Late last month another erupting filament lifted off the active solar surface and blasted this enormous bubble of magnetic plasma into space. Direct light from the sun is blocked in this picture of the event with the sun’s relative position and size indicated by a white half circle at bottom center. The field of view extends 2 million kilometers or more from the solar surface. While hints of these explosive events, called coronal mass ejections or CMEs, were discovered by spacecraft in the early 70s this dramatic image is part of a detailed record of this CME’s development from the presently operating SOlar and Heliospheric Observatory (SOHO) spacecraft. Near the minimum of the solar activity cycle CMEs occur about once a week, but as we approach solar maximum rates of two or more per day are anticipated. Though this CME was clearly not headed for Earth, strong CMEs are seen to profoundly influence space weather, and those directed toward our planet and can have serious effects.

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)