Singapore
June 2013
It was Thursday the 13th. Merlion Wayfarer looked out of her window and spotted a red moon. Incredulous, she blinked. And looked out again. A red moon.
(13 June 2013, 2150 hours)
She had never seen a red moon before - White yes, Yellow yes, Orange yes, Red no.
Moments later, the moon was obscured by the dark clouds. All that remained was one dark sky. Pitch black.
Uh-oh.
Her religious friends were filled with premonitions.
Instead of scaring herself silly, Merlion Wayfarer looked to Google for a scientific explanation...
Most of the time, the Moon is a bright yellow color; it’s reflecting light from the Sun. But sometimes the Moon can turn a beautiful dramatic red color.
There are few situations that can cause a red moon.
The most common way to see the Moon turn red is when the Moon is low in the sky, just after moonrise or before it’s about to set below the horizon. Just like the Sun, light from the Moon has to pass through a larger amount of atmosphere when it’s down near the horizon, compared to when it’s overhead. The Earth’s atmosphere can scatter sunlight, and since moonlight is just scattered sunlight, it can scatter that too. Red light can pass through the atmosphere and not get scattered much, while light at the blue end of the spectrum is more easily scattered. When you see a red moon, you’re seeing the red light that wasn’t scattered, but the blue and green light have been scattered away. That’s why the Moon looks red.
The second reason for a red moon is if there’s some kind of particle in the air. A forest fire or volcanic eruption can fill the air with tiny particles that partially obscure light from the Sun and Moon. Once again, these particles tend to scatter blue and green light away, while permitting red light to pass through more easily. When you see a red moon, high up in the sky, it’s probably because there’s a large amount of dust in the air.
A third - and dramatic - way to get a red moon is during a lunar eclipse. During a lunar eclipse, the Moon passes behind the Earth’s shadow, which darkens it. If you could take a look at the Earth from inside its shadow, you would see that the atmosphere around the edge of the entire planet glows red. Once again, this is because large amounts of atmosphere will scatter away the blue/green light and let the red light go straight through. During a lunar eclipse, the Moon passes fully into the shadow of the Earth and it’s no longer being illuminated by the Sun; however, this red light passing through the Earth’s atmosphere does reach the Moon, and shines on it.
|
Hmmm, #3 is unlikely as there was no lunar eclipse forecasted on 13 June 2013. The last lunar eclipse was on 25 May 2013. The next lunar eclipse is on 18 October 2013.
(Space.com, 2013)
The Moon's eastward motion is much slower than the sky's westward motion. So, though moving to the east from day to day, it still has a net motion toward the west, each day. This means that it still rises in the east, and sets in the west, like the stars, but a little later, each day.
Despite a forecast of an earlier moonset at 2249 hours on 13 June, the crescent moon was yellow on both 12 June and 14 June.
Hence, the most likely reason was dust particles in the atmosphere.
"The exact color that the moon appears depends on the amount of dust and clouds in the atmosphere," according to NASA scientists. "If there are extra particles in the atmosphere, from say a recent volcanic eruption, the moon will appear a darker shade of red." (Space.com, 2013)
Merlion Wayfarer recalled that the PSI reading from Wednesday was at 59. On Friday, it jumped to 91. The 24h reading shows a high degree of particulate matter (PM2.5 and PM10). It was also an unusually warm evening with still air on 13 June, an indication of wind shift.
A check on the NEA website confirms this:
Hazy Conditions Update
(Updated on 14 June 2013)
Southwest Monsoon conditions have onset over the region since the beginning of the week, with low level winds blowing predominantly from the southeast or southwest. The Southwest Monsoon season typically last from June to September and is the traditional dry season for the southern ASEAN region.
In the coming months, occasional extended periods of drier weather can be expected in the region. During the season, increased hotspot activities may be expected in Sumatra and Borneo. In addition, transboundary smoke haze could affect the region during periods of persistent dry weather conditions.
In recent days, weather conditions in the region have become drier and an increase in hotspot activities has been observed mainly over central Sumatra. 85 hotspots were detected on 6 June 2013 over Sumatra. Due to more cloud cover over Sumatra yesterday, the number of hotspots detected on 13 June 2013 has decreased to 22. Singapore was affected by slight haze since yesterday. The haziness and burning smell are from the fires in Sumatra, brought over by prevailing winds blowing from the southwest or west during the current Southwest Monsoon season. Hazy conditions are expected for the next few days.
|
Sources
