Double rainbows, supermoons, iridescence and other phenomena in a sky are separate events

March 4, 2017 - Supermoon

Something seems to be adult with a sky these days – what with a supermoon that is some-more super than others, surprising rainbows and pinkish and purple sunsets showering a city.

In Nov final year, a universe saw a biggest supermoon in roughly 70 years.

Twice in a final 6 months – on Sept 30 final year and Jan 30 this year – double rainbows spanned a skies of Singapore after it rained. The second one seemed on a third day of Chinese New Year, to a pleasure of some people. In Chinese culture, a double rainbow is deliberate auspicious.

Then, on a afternoon of Feb 20, sightings of what was primarily suspicion to be a glow rainbow – imitative Paddle Pop ice cream – took amicable media by storm. The Meteorological Service Singapore (MSS) after simplified that it was not a glow rainbow.

In a final few months, Singaporeans have also been treated to some pinkish and purple-hued sunsets. According to citizen broadcasting website Stomp, one of those sunsets took place on a dusk of Feb 4.

So, what is function adult there?

Experts whom The Sunday Times spoke to contend a several occurrences are not associated and that they start for opposite reasons.

Associate Professor Koh Tieh Yong, a continue scientist from UniSIM, records that a supermoon is not a meteorological phenomenon, though one of astronomical mechanics: It is a full moon that is during a nearest stretch from Earth, so it appears bigger and brighter than usual.

“A supermoon’s occurrence follows a unchanging settlement according to a periodicities of a moon’s circuit around Earth and Earth’s circuit around a sun,” he says. This formula in 4 to 6 supermoons in a year on average, he adds.

As for a double rainbows and iridescence, an MSS orator says they are common windy visible phenomena shaped when sunlight, flitting by a atmosphere, is scattered, diffracted, reflected or refracted, producing a charming coming in a sky.

A rainbow is shaped when object is refracted and reflected opposite raindrops in a sky. And a double rainbow appears when light is reflected twice inside a raindrop instead of once.

As for a glow rainbow, it is shaped when object is refracted by ice crystals in high-altitude cirrus clouds. Unlike rainbows, iridescence is caused by diffraction (when light bends). In shimmering clouds, object bends around cloud H2O droplets or ice particles rather than flitting by them.

According to a MSS spokesman, double rainbows and iridescence are naturally occurring phenomena and might not always happen.

Assistant Professor Winston Chow from a National University of Singapore’s embankment dialect adds: “It’s some-more expected that a specific continue conditions were only right for both to occur.”

For instance, he records that 3 conditions are indispensable for a double rainbow to occur: a dark, pale and stormy sky in a distance; a object during a low angle (early morning or late afternoon); and a chairman saying a rainbow has to be in a place where a sky behind and above him is transparent so that object can pass by unfettered to be reflected or refracted behind to him.

“The pivotal to saying a double rainbow is a pointy contrariety between balmy and stormy locations ,” he says.

While a scholarship behind these phenomena might take a layman a while to grasp, it is good news for shutterbugs such as veteran photographer Jacqueline Choo, 36. She did not locate a double rainbows and a shimmering clouds, though loves a “beautiful pinkish and purple-hued sunsets”.

Prof Koh says sunsets are many charming when a sky is clear.

Ms Choo says: “That and a new photos of cloud iridescence have desirous me to demeanour skywards for print opportunities.”

Double rainbow

A double rainbow seen over Singapore on Jan 30. PHOTO: COURTESY OF TERENCE YEO

When: Sept 30 final year and Jan 30 this year
Where: Most sightings were reported in executive Singapore and a Central Business District.
How: Rainbows are shaped when object is refracted and reflected inside raindrops in a sky.

A double rainbow is a outcome of light undergoing thoughtfulness twice inside a raindrop, instead of once, giving arise to a primary rainbow from one inner thoughtfulness and a delegate rainbow from dual inner reflections.

This causes a delegate rainbow – that is above a primary one – to have fainter colours that are in retreat order.


A print of a moon taken in Bedok Reservoir Road on a morning of Nov 15 final year, a day after a supermoon occurred. PHOTO: JEFFREY LIM

When: Nov 14 final year
Where: All around a world
How:The tenure supermoon was coined by American astrologer Richard Nolle in 1979. 

He tangible a supermoon as a new or a full moon that occurs when a moon is within 360,000km from Earth.

As a moon is closer to Earth than usual, it can visually seem bigger than common in transparent weather, says Mr Albert Ho, boss of The Astronomical Society of Singapore. 

The one in Nov was special given it was pronounced to be a closest full moon – during a stretch of 357,000km – to Earth given 1948. It seemed adult to 14 per cent bigger and 30 per cent brighter than a full moon when it is farthest from Earth, says Mr Ho.

There will not be another like it until 2034.

Unfortunately, due to cloudy continue in Singapore, a moon could not be seen during all on Nov 14.

Some people pronounced they were means to see it clearly when a continue privileged a subsequent day.

Mr Ho points out that there is tiny or no poignant disproportion in a coming of a moon from that of a supermoon within a day or dual of a phenomenon.

Iridescent clouds

An shimmering cloud seen on Feb 20. PHOTO: AARON TOH

When: Feb 20
Where: Several tools of Singapore in a afternoon
How: In shimmering clouds, object bends or diffracts around cloud H2O droplets or ice particles rather than flitting by them.

The light afterwards recombines to give several pastel colours, depending on a distance of a H2O drop in a cloud. Small cloud droplets of a same distance furnish a best visible effect, says a Meteorological Service Singapore.

However, according to Associate Professor Koh Tieh Yong from UniSIM, many clouds include of droplets in a far-reaching operation of sizes. Hence shimmering clouds are rare. In pleasant climates, many clouds tend to be thick, creation iridescence even rarer.

The shimmering cloud seen on Feb 20, says Prof Koh, is a outcome of a transitory plume of precipitation above a categorical cloud mass – called a convective mistake – being scarcely skinny and comprising regularly tiny droplets.

Pink and purple-hued sunsets

The nightfall seen during East Coast Park on Feb 20. PHOTO: JACQUELINE CHOO

When: Some evenings in a final dual months
How:Sunsets are many charming when a sky is clear, says Associate Professor Koh Tieh Yong from UniSIM.

When there are fewer clouds – for instance, during a finish of a balmy day – a colour contrasts are greatest.

The colours come from a pinch of light by nitrogen and oxygen molecules in a air.

The few clouds that are benefaction on a setting can assistance simulate a yellow, orange and red hues, and intensify a colours.

But when too many clouds are present, they retard a object and not most colour can be seen.

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