STCE's Number Puzzle

On 3 March, active region NOAA 13234 produced an X2 flare. Details were discussed in this STCE newsflash.Underneath an extreme ultraviolet image of the eruption, as taken by PROBA2/SWAP.  Those X-class flares seem to have a jolly good party, as this is already the 15th X-class event so far this solar cycle, and the 6th (!) in 2023.


So it's time we have some fun too. Underneath is a number puzzle highlighting solar activity, projects and ongoing missions so far in solar cycle 25. The aim is to find the mystery number of 11 digits by solving the 11 questions. Each answer has to be written top-down as indicated by the number for each question. The decimals and a minus sign have already been indicated. A lot of the answers can be found by scrutinizing the webpages provided in the links, and by checking the STCE newsitems.

The solution (it's a time, expressed in seconds) of the puzzle can be found here.

Good luck, and enjoy!



Q-1 – Expressed in million kilometers, what has been the closest distance between Solar Orbiter and the Sun so far?

Q-2 – The USET telescopes at the Royal Observatory of Belgium (ROB) observe the Sun in white light, H-alpha (in the red portion of the solar spectrum), and in Ca II K (in the blue portion of the solar spectrum). What is the wavelength (in nm) corresponding to the Ca II K line?

Q-3 – For which Kp level do PECASUS operators (see Kauristie et al. 2021)  issue a “Severe HF COM” advisory for auroral absorption to civil aviation (ICAO)?

Q-4 – What is the NOAA number of the largest sunspot group that has appeared so far during Solar Cycle 25 (SC25) according to the NOAA/USAF network?

Q-5 – What is the highest daily sunspot number (final or provisional) recorded by SILSO ( ) so far this solar cycle (SC25)?

Q-6 – What is the total number of spotless days that were recorded by SILSO during the transition from solar cycle 24 to the current solar cycle 25?

Q-7 – There have been 15 X-class flares so far this solar cycle. What was the longest duration (in minutes) reached by any of these X-class events?

Q-8 – What was the number of Starlink satellites that got destroyed early February 2022 following geomagnetic disturbances during the check-out procedure in their stand-by orbit?

Q-9 – Dst-wise, what is the (preliminary) value in nT for the strongest geomagnetic storm recorded so far during SC25?

Q-10 – What was the maximum proton flux (energies greater than 10 MeV) in pfu observed by GOES during the strongest proton event so far this solar cycle?

Q-11 – What is the wavelength (in Angstrom) in which the PROBA2/SWAP instrument takes its solar EUV images?



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