Sun’s Green Flash

By Anupum Pant

More often while setting than rising, if the conditions are right, a part of the sun (on the top) can appear green. This happens for very short interval lasting for about 2-3 seconds and is considered a rare phenomenon. Since it is green and lasts for a very small interval, it is also called the green flash, emerald flash or green ray. If you have ever captured it or plan to do it in the future, do share your results with me through mail/twitter. [See the animation] [Real GIF]

What does it look like?

Sometimes the sun’s rim can appear green (in optically zoomed images). Otherwise, when the sun is set, for a brief moment, it appears as if a part of sun has separated from the main body and has turned green. It is usually seen as a horizontal line, like in the video below. But, a few lucky ones have captured complete green auras too.

Why does it happen?

The sun gives out a white light, which contains all the colors – Green is one among  them. Normally, our eye isn’t able to resolve the separate colors and sees them as a mixture which is white. When the sun sets, our atmosphere acts like a prism and bends the colors. A few colors get bent more than others. For example, green bends more than red. As a result the two colors get separated enough to be resolved by our eye. But the right amount of bending happens only if the atmospheric conditions are right.

In extremely rare cases, blue or violet flashes have been reported. [image]

For a detailed explanation you can go through this – [Geometric Optics of Green Flashes]

At poles where the sun moves in a different manner, probably the green ray can last much longer. Admiral Richard Byrd has claimed to have seen this green flash for 35 minutes while on an expedition to Antarctica.


The Coastline Paradox

By Anupum Pant

The length of Australia’s coastline according to two different sources is as follows:

  1. Year Book of Australia (1978) – 36,735 km
  2. Australian Handbook – 19,320 km

There is a significant difference in the numbers. In fact, one is almost double the other. So, what is really happening here? Which one is the correct data?
Actually, it depends. The correct data can be anyone of them or none of them. It completely depends on the kind of precision you decide to use while measuring the coastline. This is the coastline paradox.

The coastline paradox

The coastline paradox is the counter-intuitive observation that the coastline of a landmass does not have a well-defined length. – Wikipedia

The length of the coastline depends, in simple terms, on the length of scale you use to measure. For example, if you use a scale that is several kilometers long, you will get a total length which is much less than what you’d get when you would use a smaller scale. The longer scale, as explained neatly in this picture, will skip the details of the coastline.

This is exactly what happened when the two different sources measured the coastline of Australia. The first, Year Book of Ausralia, used a much longer scale than the one, Australian Handbook used. Ultimately, the great disparity in the result had to do with the precision of measurement. Had they used a scale just 1 mm in length, the result would have been a whooping 132,000 km.

This effect is similar to the mathematical fractal, Koch’s flake. Koch’s snowflake is a figure with finite area but infinite perimeter. Veritasium explains it better in this video:

Another factor is to take into account the estuaries to measure the length. Then,what about those little islands near the coast? and the little rocks that protrude out of the water surface? Which ones do you include to come out with the data?  And the majestic Bunda cliffs? Probably this article from the 1970’s clarifies what was included and what was not during the time the results were published.

So, the next time someone decides to test your general knowledge and asks you the length of certain country’s coastline, your answer should be – “It depends.”

Largest Meteorite Left No Crater On Earth

By Anupum Pant

You should know: Meteor vs. Meteoroid vs. Meteorite

Meteor: The streak of light that we see in the sky is “Meteor”. When debris enters earth and gets burned up while entering, it leaves a streak of light. Unlike what is popularly believed, meteor is not the debris itself rather the word “meteor” refers to only the flash of light.

Meteoroid: A meteoroid is a mass that is small – ranging from a kilometer to only a few millimeters in diameter. Most meteoroids that enter the Earth’s atmosphere are so small that they vaporize completely and never reach the planet’s surface.

Meteorite: If the Meteoroid survives and reaches the earth’s surface, it becomes a Meteorite.

Hoba the Meteorite

About 80,000 years back, a ridiculously huge mix of Iron and Nickel entered the earth. It was so large that what was left out of all the burning through the atmosphere, measured 66,000 kg in the end. About half ton of this meteorite has gone to laboratories for research. Even after accounting for losses towards laboratories and vandalism, it is still the largest single mass of natural Iron on the Earth’s surface. It is the largest meteorite ever discovered till date and is called “Hoba”.

This meteorite was discovered by a farmer in Namibia in the year 1920. Since then, due to its mass, it has never been moved. The meteorite and the site has been declared as a national monument by the Namibian government and several tourists visit it every year.

Farmer’s Story: 

One winter as I was hunting at the farm Hoba I noticed a strange rock. I sat down on it. Only its upper part was visible. The rock was black, and all around it was calcareous soil. I scratched the rock with my knife and saw there was a shine beneath the surface. I then chiselled off a piece and took it to the SWA Maatskappy in Grootfontein, whose director established it to be a meteorite.

If that was hardly interesting…

The most puzzling thing about this meteorite is probably not that it belongs to a very rare class of meteorites (Ataxite), but the fact that it has no crater to be seen around it. Normally, a meteorite of this size should have left a crater hundreds of meters wide.

The best theory that explains the absence of any preserved crater around it is that, this piece of rock must have hit the earth’s surface at a very low angle. As a result, it must have skipped on the surface like a flat stone on water surface. And in the end, must have landed at the place where it lies today.