Just curious to know if there is a single word in English to refer to a rare (significant) astronomic event occurrence of which is very rare or probably periodical but takes too many years to repeat itself. Also please note I am not an astronomy guy at all. To exemplify how I would like to use this term if there was one I would write (ironically):

It only occurs once in a thousand years like a rare astronomic event [here goes the word/idiom] that a lady gets attracted to me and shows interest, but I ruin the opportunity (to approach her) stupidly and have to wait another thousand years!

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    We used to call them ill omens. Back when we were into signs and portents. Feb 13, 2016 at 11:42
  • +1, Interesting. I hadn't heard about ill omens before. Feb 13, 2016 at 11:51
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    I think they're generally called "rare astronomic(al) events".
    – Hot Licks
    Feb 13, 2016 at 13:17
  • A rare astronomical event is precisely that. Could you please include an example sentence on how you plan to use the condensed form, if there was one? if you hover on the single-word-requests tag above you would see "YOU MUST INCLUDE A SAMPLE SENTENCE DEMONSTRATING HOW THE WORD WOULD BE USED; ".
    – BiscuitBoy
    Feb 13, 2016 at 13:17
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    "Once in a blue moon" is the usual astronomical metaphor to emphasize rarity of events. But I am not sure if there exists a single word that encompasses the intended meaning. If you are open to idioms and phrases, I suggest you add the tag: idiom-requests too.
    – BiscuitBoy
    Feb 13, 2016 at 13:36

3 Answers 3


The planets aligning

It only occurs once in a thousand years like the planets aligning that a lady gets attracted to me and shows interest, but I ruin the opportunity (to approach her) stupidly and have to wait another thousand years!

This idiom will make those who believe in Astrology happy. The idea that the "stars" govern the fate of your love life is as old as romance itself.

Also, it's closer to the thousand year time scale you're looking for. So it would be slightly less annoying to astronomers than say Blue Moon.

A Blue Moon happens on average about once every 2.7 years. Occasionally two full moons will fall within the same month. The second full moon is also often called a Blue Moon, but this is not the term's original meaning.

google: how often is a blue moon

Astronomers can be pretty forgiving with big numbers but they get annoyed when you're off by orders of magnitude.

When astrologers speak of the planets being aligned (something which doesn't really concern astronomers) they don't mean that the planets will actually all lie on a straight line at some instant of time. One calculation of alignments within around thirty degrees (about as close as they can get) shows that the last such alignment was in 561 BC, and the next will be in 2854. The eight planets plus Pluto are somewhat aligned every 500 years, and are grouped within 30 degrees every one to three alignments.

When was the last time all of the planets were aligned? (Beginner) by Dave Kornreich

Here the number of zeros isn't off by more than 1. That may seem a bit sloppy but understand, the only thing that really stands a good chance of happening exactly once every thousand years is the earth going round the sun for the thousandth time.

  • This is a good answer. Not sure why it was downvoted.(IMO because it is not established?) If we are looking for astronomical events in terms of rarity, alignment of planets is indeed rare. If the OP is looking for neologisms, perhaps, "A cute girl approaching me is *SO rare like the gravitational waves that it will probably take another 1.3 billion light years to happen again!*" ;)
    – BiscuitBoy
    Feb 13, 2016 at 16:07
  • As I expected Blue Moon clearly wins an ngram battle. What I didn't expect is that I had to word it as "alignment of the planets" to even get on the chart. And here I figured the idiom was at least more common then the event. :) Feb 13, 2016 at 16:13

Once in a blue moon - refers to a very rare event.

To do something “once in a blue moon” is to do it very rarely: “That company puts on a good performance only once in a blue moon.” The phrase refers to the appearance of a second full moon within a calendar month, which actually happens about every thirty-two months.

Source: Dictionary.com


If you really insist on sticking with the super-hyperbolic “1000-year” time frame, then you should go with something that actually does reoccur only that often (or something whose re-occurrence is at least “close enough for self-deprecation,” like Candied’s answer).

Personally, however, I’d reduce the time frame to either “once every 500 years,” which would render Candied’s answer totally accurate without detracting much from the impact of your hyperbole;

OR (and here’s my long-in-coming “answer”) else reduce the time frame even further to “once every 75 years or so” (or “once every lifetime or so”) and go with the fairly idiomatic:

about as often as Halley’s Comet comes around,

which, although a second sighting is possible in one lifetime, would still, I think, get your rather depressing point across adequately to most listeners/readers.
(example of usage from ‘Red Rum Comes To Light’ By Kansas Rae, via Google Books)

It only occurs once every 75 years or so, about as often as Halley’s Comet comes around, that a lady gets attracted to me and shows interest, but I [nearly always]ruin the opportunity stupidly and have to wait another lifetime or so [for it to happen again]!

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