Slashdot Mirror

← Back to Stories (view on slashdot.org)

"Blue Moon" Appears in Sky Saturday Night

Posted by Hemos on from the blue-moon-you-saw-me-standing-alone dept.

ArbiterOne writes "Tonight a rare spectacle can be seen: the second full moon in a month, which is sometimes called the "blue moon", according to CNN. Don't be disappointed if it isn't actually blue, though; the blueness is caused by increased density of smoke or ash in the air, such as after a volcanic eruption."

8 of 154 comments (clear)

  1. Not all that rare by PlazMatiC · · Score: 5, Interesting

    It's not that much of a rare occurrance .. Once every 2.7 years, even.

    1. Re:Not all that rare by Orinthe · · Score: 3, Interesting

      I don't know where this google calculator gets its numbers from, but blue moons are actually twice as common as it implies.

      There are approximately 13 lunar cycles in a year, and 12 months. Simple math should be able to tell you that there must be a blue moon on average at least once a year--rarely two, and rarely none. In fact, over the next 20 years, 17 will have blue moons.

      That's about every 1.2 years.

      --
      SELECT quote.text AS sig FROM quote NATURAL JOIN attribute WHERE attribute.description = 'witty';
      0 rows returned
  2. Rare? by MaelstromX · · Score: 5, Interesting

    From TFA:

    The phrase "Once in a blue moon" was first noted in 1824 and refers to occurrences that are uncommon, perhaps even rare. Yet, to have two full Moons in the same month is not as uncommon as one might think. In fact, it occurs, on average, about every 32 months. And in the year 1999 it actually occurred twice in three months.

    --
    audioLibre - freedom of music
    1. Re:Rare? by drang · · Score: 4, Interesting

      (treating the months as independent of each other which obviously isn't the case but shouldn't affect the outcome)

      It is not the case, it should affect the outcome, and it does. Using your figures and ignoring fractional days of a lunation, the day of the month on which a full moon occurs regresses 1-3 days each month, so if a "blue" moon occurs this month (in days 29-31) one can't occur next month (in days 26-28).

    2. Re:Rare? by Nefarious+Wheel · · Score: 2, Interesting

      And of course, in very old trade calendars (1930's or thereabouts IIRC) phases of the moon were prominently displayed with the calendar dates. If a page spilled over to another month, and a full moon was shown, it was invariably printed in blue ink.

      --
      Do not mock my vision of impractical footwear
  3. Rare? by Finuvir · · Score: 4, Interesting

    We see a full moon every 28 days. So a month with 31 days will have a blue moon if it has a full moon in the first three days. The chance of that is 3/28. The chance of a blue moon in a 30-day month is 2/28. There are 7 31-day months, 4 30-day months. So chance of no blue moon in a year (treating the months as independent of each other which obviously isn't the case but shouldn't affect the outcome) is (25/28)^7 * (26/28)^4 which is about 43.4%. So there's a 56.6% chance of a blue moon in any year.

    --
    Why is anything anything?
  4. Black Moon is even more rare by cyber_rigger · · Score: 4, Interesting

    When no full moons occur in a month (usually February).

  5. Ske & Telescope had an article about this... by MaxRahder · · Score: 2, Interesting

    See the Sky & Telescope article: "What's a Blue Moon? The trendy definition of "blue Moon" as the second full Moon in a month is a mistake." http://skyandtelescope.com/observing/objects/moon/ article_127_1.asp