Chinese Space Program - Long March - Shenzhou - Tiangong 2

We sometimes forget that it's not only the NASA, ESA or Roscosmos who are exploring space. The Chinese Space Program is running quit well. This month a powerfull Long March 2F/G Y11 space rocket launched the space craft Shenzhou-11 with two astronauts (taikonaut) to their space lab Tiangong-2. This is currently visible at night when it's crossing your area - see heavens-above for more information at your location.

DIY Making solar pictures using your DSLR on PST

How to make pictures using your DSLR on PST.  Using my D60 it's difficult to make prime focus pictures on the PST40. That's why I changed strategy and take pictures afocal using zoomlens 8-24mm with 24mm zooom. In order to bring the sun's surface into focus I need about 53mm to bridge. For that I need to install some spacers and finally the Nikon T-ring.

Sun on oct 30, 2016

Some small active regions on the sun with a couple of bright prominences.

Picture taken using PST Coronado 40 -f/10 and 24mm oculair.

300 days to the Eclipse

On August 21, 2017, a total eclipse of the sun will be seen across big parts of the United States of America. See also Great American Eclipse.

Light Pollution Map

How dark is your sky at night? See latest Light Pollution Map.  Thanks to efforts from the city council of #Scherpenheuvel-Zichem we have in my city a much darker sky then the years before.

Light Pollution Map 2015

Light Pollution Map 2016

Mova Globes

http://movainternational.com/  is the weblink to very original globes which move around with no use of cords, no batteries ... only powered by light and earth magnetic field. Different sizes are available with both space globes as our own earth. I saw those globes the first time in Paris, "maison de l'astronomie" and also in Chicago, Adler Planetarium. I would say ... great gift.

Chromatic Aberration CaF2 material - FCD100 Hoya & FPL53 Ohara

As lenses (like in refractors) have different refractrive properties depending the wavelenghts and the fact that the focal length of a lens is depending the refractiveness results in colors not focussing into a one single point behind the lens. This means that colors will shift in pictures (color glow around moon, planets) which we call chromatic abberation.

Over time refractors became better with double lenses (achromatic lens; the lenses compensate for two wavelengths) and triple lenses (apochromatic lens, lenses compensate for three wavelenghts). For the latter one the flint lens is made of ED glass. This is glass with a very low dispersion properties or high refraction indeces. Typically CaF2 is favorite but expensive, heavy and difficult to manufacture. Therefor the use of other fluorite glasses are used. Currently the use of FPL53(Ohara, JP) and FCD100 (Hoya, JP) are common in small f/ratio refractors and closing the gap with CaF2 glass.

The table below shows that the bigger the F/ratio the lower the chromatic aberration.

Looking into the data, FCD from Hoya has a slightly better refractive indices then FPL53