Author Archives: Michael Großmann

Reflected pillar & rays in windows

On April 9th, 2014, Uwe Bachmann observed a pillar of light, produced by sunlight falling onto the building of the European Central Bank (EZB) in Frankfurt. He was observing from the German Weather Service’s (DWD) headquarters in Offenbach, i.e. from a distance of 3 kilometers.

For his first photo taken at 6.17 UTC, the sun was at an elevation of 13.9° and at an azimuth of 94.8°. The upward beam of light is thought to be produced by reflection from the building’s front, which is at an angle of 9° to the vertical, with scattering from aerosol producing the luminous pillar.

With the rising of the sun and the changing of its azimuth, this pillar is “cut down” subsequently. The second photo shows the situation at 06.35 UTC for a solar elevation 16.8° and an azimuth of 98.4°. The skewness of the reflected beam of light at an angle of 45° is evident.

The last photo taken at 06.52 UTC for a solar elevation 19.5° and an azimuth of 101.8° shows the beam being reflected almost at a right angle. Here, the azimuth of the sun is almost coincident with the observer’s.

More pictures: 1234

Author: Michael Großmann,Kämpfelbach & Uwe Bachmann DWD, Offenbach, Germany

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Fraunhofer lines in rainbow ?

Fraunhofer lines are dark lines in the sun’s spectrum. They are caused by resonant atomic absorption of the sun’s thermal continuum radiation by photospheric gases.

The lines provide clues to the chemical composition of the solar atmosphere, as well as its physical conditions like temperature, pressure, magnetic fields etc.

My rainbow photography dated 11.Oct.2013 showed some greyish bands in the yellow.

Are they traces of the strongest Fraunhofer lines or artifacts of the camera’s sensor being unable to profile intermediate colors?
Is it possible at all to obtain spectral lines in nature without a prism or grating?

Author: Michael Großmann, Kämpfelbach, Germany

“Spektrodrom” – A Laboratory of Rainbow

The simulation of rainbows of many orders with hanging or standing water drops and laser light is straightforward, but often unrealistic due to deformation of the drops. Therefore, a modern version of Billet’s experiments was designed, which uses a laminar cylindrical flow of water, and white light by just a few pixels of a video projector. It is surrounded by a circular projection screen. Using slightly skewed rays, which are therefore “climbing” up the cylindrical beam of water and exiting from it in proportion to the number of partial reflections, is able to produce a simultaneous display of the first six rainbow orders in white light.

The 2nd and 3rd order.

The 1st, 4th and 5th order.

The first 4 orders.

Both 1st and 2nd orders.

Both 3rd and 4th orders.

The first six orders.

Animation about the different refraction angle beetween salty water and fresh water.

Author: Michael Großmann, Kämpfelbach, Germany

Deformed Glory

Matěj Grék placed a strong halogen lamp somewhere around 20m away and take some photos from a fogbow. He noticed that the glory was deformed. The wind was strong in this night, the fog was moving quite fast, and with the fog of course also tiny water droplets. Maybe that’s why the glory is deformed in connection with divergent light. Images are taken with a polarization filter.

Camera: Nikon D60; F/6,3; f/30mm; t=30sec. at ISO 200

Author: Matěj Grék & Michael Großmann, Kämpfelbach, Germany

Dark ring around the sun

“On the afternoon of 16th November I noticed a dark ring around the sun outside of an aureole. However, the effect could be catched better with the naked eye than the photographs assume.” (2)

“I took some picture in close succession, but none of them shows the ring. Conspicuously, the ring was distinguished by high regularity and evenness. Subsequent enhancing of the contrast let the dark ring become visible clearly on these pictures.”

Quite often, you can spot clouds moving in front of the sun. With a little luck and a cloud layer, that isn’t too thick, beautiful halation and aureoles can be seen at these conditions.

Since a cloud act as an obstacle, it causes a shadow. Apriori, this shadow is invisible to the observer. But if the shadow is projected onto a lower layer of haze, the shadow gets visible in the haze.

Hence, the example above generates a dark ring around the sun, induced by altocumulus cloud shadows on the hazes below.

Time : 16 November 2011
DSLR Camera : Nikon D 3100
Exposure : 1/500 sec, f/22#18mm, F/11, ISO 100

Author: Alec Jones, Bolton/Lancashire, United Kingdom; Michael Großmann, Kämpfelbach, Germany

Spider silk glitter path

While taking a walk, I noticed a field that was covered with fine spider silks. The sun was rather low (about 10°) and made a kind of lower light pillar appear in the silks. When I took a closer look, I could also see concentric circles of light with the sun in their centre.(2)

These circles are caused by the perspective and the angle in which the light strikes the surface of the spider silks. The light gets reflected best to the observer when the reflecting surface is positioned at an angle of 90° to the source of light. A similar effect can be observed when a street lamp shines throug wet branches of a tree.(3)(4)

The “lower light pillar” can be seen better because the sun as the source of light shines vertically down onto the field and all spider silks in this direction reflect the light towards the observer.

Place : Kämpfelbach, Germany
Time : 01 November 2011
DSLR Camera : Canon EOS 450d
Exposure : 1/60 sec, f/22mm, F/10, ISO 100

Author: Michael Großmann, Kämpfelbach, Germany

Dewbow

Dew bows are a kind of rainbows. The difference lies in the plane of projection and in the fact that static droplets are reflecting the refracted light back into the eyes of the observer. The rainbow cone resulting, the apex of which is the oberver´s eye, is cut by the plane (the field). The result is a hyperbola, but for our eyes, there is always a circle!.

The first nights in October were rather cold, so that a lot of dew could form in the fields.

I knew that the following days were ideal for looking for the dew bow.

The main problem while observing dew bows is the brightness of the field. A polarization filter makes the dew bow contrast better from the background. (2)

An even better idea was filming the dew bow while driving along the farm track. This makes it contrast even more clearly.

Place : Neulingen, Germany
Time : 02 October 2011
DSLR Camera : Canon EOS 450d
Exposure : 1/25 sec, f/10mm, F/7, ISO 100

Author: Michael Großmann, Kämpfelbach, Germany

Rings of Quételet

Rings of Quételet are caused by rays of light which had been scattered by particles of dirt on a window pane and then were reflected from the rear side of the pane, interfering with rays having been reflected from the front side of the pane and then having been scattered by the same dirt particles.

The light source itself forms a white circle being surrounded by colourful rings which are caused by interferences.

These rings always begin with a blue one right outside the white circle and end up with a red one on the other side, away from the circle, no matter if the secuence begins in the centre of the pane or on its rim.

Place : Fehraltorf, Switzerland
Time : 24 August 2011
Digital Camera : Canon EOS 450D
Exposure time : 1/2500 sec , f/9 ,Focus length 22mm, ISO 100

Author: Michael Großmann, Kämpfelbach, Germany

The crossed bows

What kind of rainbow is that? This is no fake this is real! Ok…it’s a little trick with an open window and the right angle to the sun.

The rainbow are produced with a water spray bottle. The right bow is the “real one” and the left bow is the reflected one.

The reflected surface in this example is the window in vertical direction, so the bows looks like a “x”. (2)

Place : Pforzheim, Germany
Time : 18 May 2011
Digital Camera : Panasonic DMC-FZ50
Exposure : 1/200 sec , f/3.6 , ISO 100

Author: Michael Großmann, Kämpfelbach, Germany

A single water drop

A slight-projector and a singel water drop shows a lot of bows. Here you can see the primary, secondary and tertiary bow.

The distance between the water drop an the projection backside (white paper) is 30 mm, waterdrop an light source has an diameter of 2 mm.

Photo taken on 28.07.2011 on my desktop 🙂

Author: Michael Großmann, Kämpfelbach, Germany