Tuesday, 11 October 2011

What makes a halo around the moon?

Halos around the moon – or sun – are a sign of thin cirrus clouds drifting high above our heads.
Photo credit: normalityrelief
Sometimes you look up on a clear night and see a huge circle, or ring, of light around the moon. This circle is called alunar halo. We get many messages each month from people who’ve seen rings around the moon. They’re pretty common, but they’re so mysterious looking that people often express amazement upon seeing them.
Notice in the photos that the sky looks fairly clear. After all, you can see the moon. And yet halos are a sign of high thin cirrus clouds drifting 20,000 feet or more above our heads. These clouds contain millions of tiny ice crystals. The halos you see are glints of light from these ice crystals, which have to be oriented and positioned just so with respect to your eye, in order for the halo to appear.
That’s why, like rainbows, halos around the moon – or sun – are personal. Everyone sees their own particular halo, made by their own particular ice crystals, which are different from the ice crystals making the halo of the person standing next to you.
The lunar halo photo at right is by master sky photographer Dan Bush.
Because moonlight isn’t very bright, lunar halos are mostly colorless, but you might notice more red on the inside and more blue on the outside of the halo. These colors are more noticeable in halos around the sun. If you do see a halo around the moon or sun, notice that the inner edge is sharp, while the outer edge is more diffuse. Also, notice that the sky surrounding the halo is darker than the rest of the sky.
By the way, there’s an old weather saying: “ring around the moon means rain soon.” There’s truth to this saying, because high cirrus clouds often come before a storm.

‘Moonbow,’ Hunter’s Moon light up D.C. sky

(Photo courtesty of Eric Hian-Cheong)

An unusual lunar halo lit up the skies over Washington Monday night, a display of celestial grandeur on par with the moon reaching “super” status in March.
The halo — also known as a “moon rainbow” or “moonbow” — appeared around 11:30 p.m., to the delight of local Twitter and Facebook users, who quickly started asking questions like, “How does a#moonbow even happen?”

Well, according to the Ask an Astronomer blog from Cornell University, moonbows are caused by the light of the moon passing through a thin layer of ice crystals in the upper atmosphere. The crystals refract the moonlight the way water droplets refract sunlight to produce a rainbow.
On the heels of the moonbow, the Hunter’s Moon will make an appearance over D.C. tonight. According to the Farmer’s Almanac, the Hunter’s Moon, also called the Blood Moon, is the smallest full moon of the year and should be at its fullest shortly after 10 p.m. Fingers crossed that the rain clouds hold off until then.

Thailand flooding leaves hundreds dead, threatens capital

Thai mahouts ride their elephants through the flooded Ayutthaya streets on October 10, 2011.



From Kocha Olarn, CNN
October 10, 2011 -- Updated 1849 GMT (0249 HKT)
  • Nearly 500 people are dead in Thailand and Cambodia
  • Officials order measures to protect Bangkok
  • The region has seen weeks of heavy rain
Bangkok, Thailand (CNN) -- As the death toll climbed Monday from flooding in Southeast Asia, officials beefed up flood prevention measures to protect Thailand's capital from rising water.
Millions have been affected by the flooding in Thailand and Cambodia, which has been hit by an above-average monsoonal rainy season. As of Monday, 269 people were dead in Thailand and four were missing, according to the country's Flood Relief Operations Command. Another 207 people were dead in Cambodia, according to the country's state-run news agency AKP.
Patients in two hospitals in Thailand's Ayutthaya and Nakhon Sawan provinces had to be evacuated after water reached the first floor, the flood operations command said.
Multiple tropical systems have moved over the area in recent weeks, enhancing monsoon rains and leading to the flooding. Another low pressure system is forecast to move into Southeast Asia on Tuesday and Wednesday, said Brandon Miller, senior meteorologist for CNN International.
On Monday, Thai Prime Minister Yingluck Shinawatra ordered canal dredging and reinforcement of flood-prevention embankments to protect Bangkok, state-run news agency MCOT reported. In addition, three new flood-prevention walls were being built at two locations in Rangsit, in northern Bangkok, and in Taling Chan, in the western part of the city.
The government needs another 1.5 million sandbags, MCOT reported. The prime minister called on the private sector to supply them, but said the government will buy all the needed sandbags by Wednesday, the news agency said.
The Rojana Industrial Park has halted operations for the time being, director Amara Charoengitwattanagun told MCOT, and the facility may be further damaged if the flooding worsens. One plant in the park, Single Point Parts, evacuated all workers from the premises and built flood prevention embankments around its building, according to MCOT.
Meanwhile, Honda Thailand said on its website Monday that its plants in the Rojana park are flooded and will be closed until at least until the end of the week.