SC24 and the NOAA-scales

Once again, solar activity has been very low last week. One could wonder how poor the performance of ongoing solar cycle 24 (SC24) has been compared to the previous solar cycles. For that, one could use the famous NOAA-scales which link objective solar parameters such as the x-ray flux to all kinds of practical space weather effects such as on radio communication. More details can be found on the NOAA/SWPC webpage.

The Sun 10 years in STEREO

Early October 26, 2006 the two STEREO spacecraft were launched. The twin spacecraft had to observe the Sun in stereo. Both have a similar orbit as the earth, one ahead, the other trailing behind.

The title of ‘Corresponding Astronomer’ goes to ….

And the title of ‘Corresponding Astronomer’ goes to …. Prof Jean Lilensten.

Jean Lilensten, research director of CNRS at the University of Grenoble, is a welcome guest at the Observatory and the Solar-Terrestrial Centre of Excellence. 

Sunspot gets a facelift

NOAA 2599 transited the solar disk from 3 till 15 October. It reached its largest size around 5 October, when its area was equivalent to nearly 3 times the total surface area of the Earth. During its transit, it significantly changed from outlook, becoming smaller and less complex. Solar observers watching the Sun only at the beginning and the end of the period might even have had a hard time to conclude this was the same sunspot.

So long, filament!

A filament eruption took place early on 1 October (see movie). This filament had a respectable length of about 40 degrees, i.e. more than 10% of the solar circumference or well over the average Earth-Moon distance. The feature was already visible during the previous solar rotation early September, when it transited the solar disk uneventfully (see this news item).

Return of the Behemoth

A huge trans-equatorial coronal hole (CH) is transiting the solar disk. According to the latest data from LMSAL/SPOCA (28 September), the total coronal hole area is the equivalent of about 880 times the total surface area of the Earth. It is by far the largest CH since the last solar cycle maximum, even dwarfing the large southern polar CH from late 2014 - early 2015 (see the 2014 space weather highlights).

Farside eruption

For the second consecutive week, no C-class flares were observed from Earth. In fact, not a single C-class flare has been recorded so far this September month, with the last C-class event dating back already from late on 31 August. Records will not be broken soon though, as the longest period without a C-class flare was set during the past solar cycle minimum from 3 April till 3 November 2008 (213 days!).

Collateral damage

Solar flare activity was not particularly impressive last week, with no C-class events at all. Fortunately, a B7.9 flare peaking at 03:23UT on 09 September in active region NOAA 2588, was associated with a lovely post-flare effect: the disappearance of almost an entire filament about 10 degrees to the southeast of this active region.

Resuscitating STEREO-B

On 1 October 2014, communications with the STEREO-B spacecraft were interrupted during a planned test in anticipation of its solar conjunction at the Sun's farside (see image underneath for positions relative to Earth). Despite intense recovery efforts in the subsequent months, contact could not be re-established and the spacecraft seemed to be lost. More background information can be found in the news items of 4 June 2014 and 29 July 2015.

Sun-grazing comet mystery

Comet tail seen by LASCO/C2

Did the EUV space telescope onboard PROBA2 see the sun-grazing comet as a tiny dot on the solar surface lightening up? This is the story of 5 mysterious pixels.



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