Saturday, June 30, 2007

People living in different parts of the world may get confused when searching the internet for the term "Blue Moon". The present definition of this phenomenum is when two full moons occur in the course of one month. Parenthetically, the term "black moon" is when a month has no full moon. This can only occur in a February because the lunar cycle is slightly longer than a regular 28 days(about 29.5 days). The moon in such a month is, however, so close to visibly full that the casual observer will "think" there is a full moon in such a month even though there is not.
Today's full moon arrived at 13:49 GMT (8:49 Winnipeg time- daylight savings time). Is today's full moon a "blue moon" here. No...because the last full moon was on May 31st at 20:04. It was May that had a blue moon here and elsewhere in the western hemisphere.
But it is a little more complicated than that. The eastern hemisphere does have a blue moon this month because there are full moons on both June 1st and June 30th there. The point where this ceases to be true is two time zones heading west across the Atlantic. Not the best place in the world to set up a telescope. But let's go further. Near the Pacific international date line the month that has a blue moon is neither May nor June. It's July. Auckland New Zealand for instance has a full moon at 01:49 July 1st and another at 12:48 July 30th. If you want further details on this go to the Blue Moon Page and hunt for the "longer answers". The Wikipedia encyclopedia has a more general article on the whole matter of blue moons.
But in any case the Moon is full, and it's time for Molly to hop in her little cruise ship, 'Selena', and go sailing down the lunar seas on her long interupted lunar voyage.
Look at the above lunar map. Mare Frigoris is labelled # 6 in that diagram. It is the northernmost (highest "up") major lunar feature. It lays just north of the Mare Imbrium (see later) and stretches eastward (to the right) above the Sea of Serenity. Like the other lunar "seas" Frigoris is dark because its basin is filled with lava that flowed after impacts on the early Moon by other bodies. This sea is bounded on the south (below) by the Montes Alpes on the east (right) and the Montes Jura on the west (left) and the Montes Teneriffe in the middle.. The mountains of the Moon are generally named after other mountain ranges on Earth. If you look a point just to the left and down from the number six in the above diagram you will see a dark smudge. This is the crater named Plato. Lunar craters are named after people with an emphasis on astronomers, scientists, explorers and other political and religious people from the past. There are hundreds of recognized names for lunar craters. Plato essentially marks the division between the Juras/Teneriffes to the left and the Alps to the right. Plato, about 100km wide, is extremely dark in colour and thus is one of the easiest lunar craters to spot if you are using binoculars that are less than ideal. Less easy to spot is the crater Cassini just south (down) from the Alps where this mountain range runs into the Montes Caucasus which bound the Sea of Serenity on its northwest. in the approximate middle of the Alps there is the 'Alpine Valley' that seems to bisect the mountain range in half. This is a shock ray from the impact that created the Mare Imbrium to the south.
That's it for now. The little pea-green ship Selena is now pulling up to dock. Stay tuned for when we sail again for the Sea of Rains.

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