Once in a Blue Moon? You mean once every two and a half years. Blue moons are rare occurrences, but are not as rare as people think.

Tonight, the world will experience a “blue moon”, according to the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA).

But in this case, the moon doesn’t literally turn blue. The moon is called blue when it’s the second full moon within a month. Usually, there is only one blue moon in a month, with of course, the exception of blue moons.
The lunar cycle is 29 days long, which means that eventually, there will be an appearance of two moons in one month. This usually happens when a full moon appears at the very start of the month, either on the first or second day.

A blue moon happens roughly once every two and a half years on average, the last two happened in August 2012 and July 2015. In rare cases, there are two blue moons in one year. The “double blue moon” occurred last 1999, and will happen again this year – one tonight, and another in March. On the other hand, when double blue moons occur in January and March, February does not have a full moon, partially because it only has 28 days.

Bluer than Blue
There have been cases of an actual “blue moon,” which are rarer than its conventional meaning. The moon changes hue when there are volcanic eruptions or large fires that leave particles in the atmosphere.

One of the longest times a blue moon occurred was when the Indonesian volcano Krakatoa erupted in 1883, equal to the blast of a 100-megaton nuclear bomb. People reported to have heard a cannon-like noise up to 600 kilometers away. Ash and particles about 1 micrometer wide rose up to the Earth’s atmosphere, causing selective light to pass through and reach the surface. The moon “turned blue” for days in areas near Krakatoa.

Reported sightings of a “blue moon” also happened after Mount Pinatubo erupted in 1991. Forest fires are also a cause for blue moons because of the smoke and particles they create. In these occurrences, “lavender suns” are also reported to be seen, also caused by particles in the air.

Historical Mix-up
Originally, the blue moon was considered the third out of four full moons in a season (winter, spring, summer, fall). Each season usually experiences 3 full moons, hence the appearance of a 4th moon, or the Blue Moon, which came rarely and is considered the 13th moon in a year. This was based on Maine Farmer’s Almanac from 1819, which farmers used as reference for agricultural purposes.

However, in 1946, an article on Sky & Telescope misinterpreted the blue moon as the 2nd moon in a month, inferring from the idea that the blue moon appeared as the 13th full moon in a year. The article was titled “Once in a Blue Moon”, a phrase which integrated itself into pop culture meaning something that happens very rarely.
From this misinterpretation, a blue moon can be considered either of the following:
1. It is the extra full moon within a season, which usually has three moons (Maine’s definition); or
2. It is the second full moon within a month (Sky & Telescope’s definition).

The latter is the more popular and commonly used definition for a blue moon nowadays, with the other definition practically defunct.

Catch the blue moon tonight, peaking at 8:51 PM (Philippine Standard Time).

SOURCES:
http://www.seasky.org/astronomy/astronomy-glossary.html#B
www.skyandtelescope.com/observing/what-is-a-blue-moon/

PAGASA
NASA

Because we are now experiencing the first full moon of the year, here are some interesting lunar facts:

1. It will take 29.5 days, the equivalent of a lunar cycle, to see the moon full again.

2. The second full moon that occurs within a month is called a Blue Moon. This is a rare phenomenon that occurs about every three years. That is why rare events are described as “once in a blue moon.”

3. February is the only month that can have NO occurrence of full moon.

4. While some who suffer from insomnia claim that they cannot sleep during the full moon, others say they sleep more soundly during this time.
5. Though the full moon looks like round, it is actually shaped like an egg with its end point facing the earth.

‘Tis the season to be merry as we are lucky enough to see the rare Christmas Full Moon tonight at 7:11 PM according to PAGASA. The last recorded Christmas Full Moon was in 1977, and tonight, it will be clearly seen again on a cold starry night after 38 years. But because we are a tropical country, the chance of isolated thunderstorms is always present. However, if skies remain clear, you’ll see the moon in its full glory tonight. The next time this phenomenon will happen will be in the year 2034.

The only downside is that when the moon is full, high tide occurs, making low-lying areas susceptible to flooding.

Aside from preparing your Christmas presents and gearing up for get-togethers, another exciting thing to do this December is to watch the skies—not to wait for Santa and his reindeer, but to witness the spectacular meteors!

Meteoroids VS Meteors & Meteorites
Meteoroids are small rocks or particles orbiting around the sun. Once a meteoroid enters the Earth’s atmosphere, it vaporizes and becomes a meteor, also known as a “shooting star” or bulalakaw in Tagalog.
According to the National Aeronautics and Space Administration (NASA), as this space rock falls toward the Earth, the air resistance or drag makes it extremely hot. So what we see is not actually the rock, but the bright streak or the glowing hot air as it approaches the atmosphere.

If a small asteroid or large meteoroid survives its entry or passage through the atmosphere and lands on the surface of the Earth, it is called a meteorite.

December is an ideal month for astronomy enthusiasts as the Geminids Meteor Shower lights up the sky from December 4 to 17, 2015. Appearing to come from the constellation of Gemini, Geminids meteors do not originate from a comet, but from an asteroid. Meteors from this shower are very rocky and are more visible.

NASA explains that these meteors originated from the Asteroid 3200 Phaethon, which takes 1.4 years to orbit the sun. Phaethon is a small asteroid with a diameter of 5.10 kilometers.

Dubbed as a “dead comet”, the Phaethon does not develop a cometary tail when it passes by the sun. Its spectra look like a rocky asteroid instead.

3200 Phaethon was discovered by the Infrared Astronomial Satellite on October 11, 1983. Due to its close distance to the sun, Phaethon is named after the character in Greek mythology that drove the chariot of Helios (the God of Sun). But it was the astronomer, Fred Whipple, who recognized that the Geminids meteor shower originated from Phaethon.

The Geminids is considered as one of the best and most reliable annual meteor showers. So mark your calendars now! Its peak activity is on the late night of December 14 until the early morning hours of December 15. PAGASA says that if good weather permits, an observer can witness around 40 meteors per hour.

Viewing Tips
– Get as far away from urban pollution as possible. Find a location with a clear or almost cloudless night sky.
– Search for the darkest patch of sky.
– Clothing matters! Wear clothes that suit cold overnight weather.
– Bring something comfortable for you to sit or lie down.
– It takes time, so be patient.
– Put away the telescope or binoculars, which may reduce the amount of sky you can see at once.
– Relax your eyes. Do not look at any specific spot.
– Avoid looking at your gadgets or any other light source which could disturb night vision.
– If you have to look at something on the surface of the Earth, use a red light.

Sources:
NASA
PAGASA-DOST
www.universetoday.com