Friday 25th of January, I wanted to test my 102mm refractor on some difficult double stars, Orion was well placed and the lunar libration interesting, but… what is the link between double stars and the moon, we'll see ...
First Rigel, the sixth brightest star in the sky, so blue, spectral class B8, and his girlfriend Rigel B Class B9 faint, the same blue and very poor magnitude 10.4 is very close 9.5” only, quite hidden in the shine of Rigel.
Then I went to Sigma-Orionis
This star is very easy to find (m3.7), close to Alnitak, this I a multiple star, two stars m6.6 and especially for me a faint star near Sigma (m8.8) that’s interesting.
Another multiple star is called Struve 761, the name of an astronomer specializing in double stars. This star (m6.8) is included in the same field as Sigma and is triple, the other two components are very close (m8.4 and m8.6).
This asterism is very nice to catch, try to point your telescope there, during a winter night.
Mr. Struve has his name on a moon crater, but as usual nothing is simple, it is necessary that the lunar libration reveal this limb crater. This was the case tonight.
Struve crater is part of a system of old impact craters flooded by lava.
Struve is 180km in diameter, irregular walls climb up to 1700m. Another crater very close, with a diameter of 100km, is called Russel. Russell was an astronomer and an artist, the circle is complete!
The first sketch is the Rigel's one, Is there any possibility to post multiple sketches ?