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All Coronal Holes Great and Small


During the last fortnight, two coronal holes (one on each solar hemisphere) transited the solar disk, as shown in this clip from GOES15/SXI imagery. Passing the disk's centre around 22-23 April, the high speed gusts of energetic particles created active geomagnetic conditions on 25 April and even a brief minor storm period on 26 April.

Birth of a sunspot group


It's always impressive to see sunspots develop from scratch, and cluster into an ominously looking sunspot group. Early on Friday 19 April, magnetic fields pushed through the solar surface and did just that in less than 24 hours. NOAA 1726 was born, and it was a quite large group: In the image underneath, there is room to easily fit 10 Earths between the outer edges of the two main spots!

M6.5 flare in NOAA 1719


No doubt about it: The M6 flare in sunspot group NOAA 1719 was the highlight of last week's space weather activity.

A movie was created showing the various aspects of this flare and its impact on Earth. Some additional details can be found underneath.

A magnetic mirage


Sunspots are magnetic disturbances on the surface of the Sun. This was discovered back in 1908 by George Ellery Hale. In the next few decades, technology improved and during the 1950's and 60's, Horace Welcome Babcock and Robert Benjamin Leighton developed the magnetograph (see note 1) to display the magnetic field of the entire Sun. These maps are known as magnetograms. They show essentially white and black patches, mostly corresponding to active regions and sunspot groups (See 4 April 2013 SDO image underneath).

The numbers are down...


A solar flare is a sudden release of an enormous amount of energy due to magnetic reconnection in the solar atmosphere, usually above sunspot regions. This energy release takes place over the entire electromagnetic spectrum. Solar flares are often classified according to their peak strength in x-rays. Scientists usually use three categories: "C" (common), "M" (medium) and "X" (extreme), with each category 10 times stronger than the previous one. As an example: an X6-flare is 10 times stronger than an M6-flare, and 600 times stronger than a C1-flare.

M for Marvelous


One of last week's highlights certainly was the M1.6-flare in NOAA 1692 near the northwest limb of the Sun. Starting late on 21 March at 21:42UT, it reached its peak flux at 22:04UT and ended at 22:36UT. The event was not accompanied by an energetic proton enhancement.

Ready... Aim... Fire!...


The Sun took a good aim at Earth this week.

Comet Pan-STARRS swings by


From the darkness of outer space, comet Pan-STARRS has come to pay us a one-time visit before receding again into the coldness of oblivion.

The comet, officially designated as C/2011 L4, was discovered in June 2011 by the Pan-STARRS telescope on Hawaii when it was still over 1 billion kilometers away from the Sun. Last Sunday, on 10 March, the comet was closer to our home star than the planet Mercury.

10 Little Indians


During the first two months of 2013, quite a few Coronal Mass Ejections (CMEs) were visible. As an example, this movie shows the CME-activity from 23 till 28 February. The 10 most interesting events were numbered and are discussed below.

Fast rise of NOAA 1678


On 18 February, a sunspot group quickly developed to the southeast (bottom left) of NOAA 1671. According to the daily NOAA reports, fresh NOAA 1678 already reached its maximum sunspot area on 21 February, being nearly three times as large as the total area of the planet Earth.

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