AMATEUR ASTRONOMY:
THE BLUE MOON THAT ENDS THE DECADE:
Tonight, as the decade ends, we will have the unusual event of a "blue moon" to ring out the old year. The term doesn't actually refer to the moon appearing blue in colour, though this can occur given certain atmospheric conditions. If there is sufficient dust in the air then light of a longer wavelength, ie red, is scattered away from the eyes of the observer, and the light that gets through is shifted to the blue end of the spectrum. this sort of lunar colouration was most prominent after the explosion of Krakatoa in 1883, but it also occurred in the 1950s after large forest fires in Canada and Sweden. It was also reported after the eruption of Mount Pinatubo in the Philippines in 1991, and there were even reports of "blue suns" in that year (see here). I do not recall it being so, and neither do I recall any change in the colour of the Moon after this year's extensive forest fires in BC. I do recall being able to spot the atmospheric haze after the eruption at Mount St. Helen's in 1980. Does anyone else have any memories or references ?

The origin of the phrase "blue moon" event goes as far back as 1528 when it was used in an anti-clerical English pamphlet entitled "Rede Me and Be Not Wrothe" where the author mocks the clergy saying that, if they declared the moon to be blue then they would expect others to believe it. The use of the term to describe a rare event, as in "once in a blue Moon", dates from 1824 (see here). There is some dispute about the origin of the term in relation to an "extra moon". Some say that the Old Farmer's Almanac began to use the term to refer to an extra full moon in a season in the 1800s, while others claim that the Farmers' Almanac didn't begin using the term this way until the 1930s. In any case the usage of the term as referring to two full moons in a month is of even more recent vintage. It's generally accepted that this way of using the phrase began in 1946 when a writer for Sky and Telescope Magazine misinterpreted the Farmers' Almanac rule of an extra moon in a season as being an extra moon in a month. For more on the history of the term see the Wikipedia article on blue moons.




Today's (tonight's) blue Moon takes place at 19:13 UT. Here in the Central time Zone this translates as 13:13. We obviously can't observe the exact instant of the Moon's fullness here in Manitoba at a little after 1:00 in the afternoon. In Australia and East Asia the event doesn't actually occur until tomorrow, January 1, and it is January rather than December that will have a 'blue Moon' there. The actual "blue Moon" will, however, be the second full Moon of January, not the first. The time of an "exact" full Moon is, of course, an instant rather than a night in duration. If you wish to find the exact time of the full moon and to convert it to your own local time consult the Time and Date.Com site where there is a wealth of other information such as sunrise/sunset and moonrise/moonset data. For those who would like a visual representation of the Moon's phases I could suggest the Moon Phase Calender at the Moon Connection site. A "blue Moon" in the sense of a second full Moon in a month occurs about once every 2.72 years.




There is also a partial eclipse of the Moon visible in Australia, Asia, Europe and Africa tonight, though it is not visible in the western hemisphere. This event has already passed , as maximum totality happened at 19;23 UT.



For those interested in matters lunar a couple of years ago Molly featured a series of articles that were a "leisurely cruise" through the various most prominent visible features of the Moon. If you're interested just type the item that you might want to read about (such as 'Mare Criseum', sea of Tranquility, etc..) in the search function of this blog and read all about it. See you in the New Year. It's been an interesting year and an interesting decade.

RED MOONS AND BLUE MOONS:

This May is rather unique in that, at least in North America, it will have both a "red Moon" and a "blue Moon". Now these terms are rather deceptive, especially the latter. The Moon may indeed turn a reddish hue when its light is considerably dimmed say during an eclipse or when it is quite low on the horizon. The latter is the case for this year as the Moon is approaching its most southerly point in an 18.6 year long wobble above and below the plane of the ecliptic. The furthest south point of this periodicity will occur along with the full Moon of June 29/30 in North America. At that point the Moon will be a full 5 degrees below the ecliptic and will not even rise at all for points north of 61 degrees latitude. When the Moon is closest to the horizon it may take on a more orange or reddish hue, and the Moon is never closer to the horizon than when it is at the most southerly point of its cycle. The point where the Moon reverses its journey is called a "major lunar standstill", in analogy to the solar solstices. A more lengthy description of the Moon's cycles is provided at http://www.umass.edu/sunwheel/pages/moonteaching.html .

Then there is the "blue Moon". This is a term that is actually quite modern in origin. The original use of the term was coined by the Old Farmers' Almanac in 1932. The OFA suggested that when any of the four seasons contained 4 full moons instead of 3 that the 3rd should be referred to as a "blue Moon". This became misinterpreted, and the present definition is that when any month has two full moons then the second one is referred to as a "blue Moon". The blue Moon will occur on the full Moon of May 31st in North and South America, but in Australia, Asia, Africa and Europe this moon will actually occur on June 1st. This means that the old world blue moon will be on June 30th this year. Blue moons occur on the average every 32 months, but they can be more or less frequent. In 1999, for instance, there were two blue moons in the course of only three months.

This expression "once in a blue Moon" is meant to convey the idea of "rarity", even though blue moons are not that uncommon at all. The Moon can also appear to take on a blueish tinge if its light is extremely dim. This happened to the unilluminated part of the waxing crescent Moon during the recent conjunction of Venus and the Moon earlier this month, and Molly has certainly observed it at other times during crescent moons. Large amounts of soot and ash in the atmosphere can also make the Moon appear to be blue. The most recent event that led to widespread reports of "blue moons" (and even "blue suns") was the 1991 eruption of Mount Pinatubo in 1991.

CONJUNCTION TONIGHT:

VENUS AND THE MOON:

The night sky will hold a particularly spectacular sight tonight as a close conjunction between the waxing crescent Moon and the planet Venus will occur in the sky across most of North America. The two bodies will be at about a degree of separation, and the Moon will appear to the right of Venus. The "dark" of the Moon will also be visible due to the phenomenon known as "Earthshine", and the entire lunar globe will be visible as a blueish grey globe. Events such as these often bring a flurry of UFO reports to local authorities and astronomers. The point of closest approach will occur at 9:55 pm here in Winnipeg (sunset is at 9:12 pm) with bodies well up in the sky at 26 degrees. The event will occur later in the East, but the Moon and Venus will be much closer to the horizon there. As you move further to the West the Moon and Venus will be higher in the sky, but the point of closest approach will occur before sunset. In Edmonton, for instance the Sun will set at 9:33 pm while the closest approach will be at 8:41 pm. The conjunction, however, will still be visible and well worth viewing. Where the event occurs at the proper time one can see the two bodies approach each other and then draw apart.

The conjunction of the Moon and Venus occurs on the flags of many Islamic nations such as Turkey, Pakistan, Malaysia, Algeria, Mauritania and Tunisia. The poet Samuel Taylor Coleridge used it as an "ominous portent" in 'The Rime of the Ancient Mariner'.

At the present time Venus, when viewed through binoculars appears as a gibbous disc. At the beginning of June it will have evolved into a "half-moon" phase, and in July it will present as a crescent.