Double rainbow explained and Alexander's dark band.

A rain droplet functions both as a mirror and prism.

As the first, primary, rainbow is caused by refraction and reflection of sunlight within rain drops, the secundary rainbow will show up when sunlight is reflected twice within the droplet. This also explains the reason why we see the reversed order of the colors. Because of the extra reflection and thus light gets lost, we see the secundary rainbow less bright than the primary rainbow.

Another phenomenon is the area between the primary and secundary rainbow. This area is typical darker and called Alexander's band or Alexander's dark band. This optical phenomenon was the first time described by Alexander of Aphrodisias, 200AD.

Double Rainbow in Averbode

Startrail Summer triangle

Startrail of the summer triangle. This triangle is made by the brightest stars Vega, Altair and Deneb of the constellations Lyra, Aquila and Cygnus. Picture taken using by Nikon D60 and pictures stacked using Startrail.de and final modified using CS4.

Usefull Links

More astronomical links available. See my "Usefull Links Page" 

Record High Temperature

Today, October 18 2014, a record high outside temperature was registrated in Belgium. The previous record was recorded 100 years ago. In Averbode a temperature of 25,5°C was measured around 17h08.

Eclipse August 21, 2017

The eclipse of 21 august 2017 in the US will be a unique opportunity to experience a total solar eclipse combined with a visit to the US.

Interesting websites : see usefull links on this blog 

Visiting the Royal Observatory

Yesterday we made a trip to Ukkel near Brussels for visiting the Royal Observartory and the KMI Royal Weather Instute. Workshops for children and well explained experiments made this Open door day a real learning event.

Beside astronomy also information about seismology, spectroscopy, diffusion, aurora's, Gaia, interferometry, absorption, emission, meteo radars, solar-terrestrial centre of excellence and many more...

Launching of a Weather balloon. The balloon is filled with Hydrogen and will explode on a height of about 30km.

One of the many telescopes which are not in use or even not functioning any more. The use of observatory in Chili are taken over the current instrumentarium.

Royal Observatory Open doors

The fiftieth anniversary of the Belgian Institute for Space Aeronomy (BIRA), open the IASB, the RMI and the Royal Observatory their doors on Saturday 11th and Sunday 12th October.

See also this website.