The Moon and the Seven Sisters

By Phil Plait | November 12, 2008 10:21 am

The Moon orbits the Earth about once a month. As it does so, it sometimes passes directly over (occludes) bright stars and, rarely, planets. It’s a fun event to observe, actually, to see the Moon encroach upon a star, getting ever closer, and then, blip! The star vanishes behind the Moon’s limb. I’ve watched this dozens of times and it never gets old.

Sometimes, though, the Moon does itself one better. Or seven, actually: it passes in front of the Pleiades, a cluster of hundreds of stars in the constellation of Taurus. The Pleiades are a very tight formation, and only six or seven of the brightest members can be seen to the eye — they form a shape that looks a lot like the Little Dipper, and are confused for that constellation by a lot of people.

On Thursday, November 13, this will happen again. It starts around 16:00 UT and while it lasts for several hours, the timing means those of us in the US will miss it. It’s best visible in Europe, and the northern parts of Africa and Asia. It happens again on December 11, but again misses the US. Nuts.

When the Moon passes through the Pleiades, it’s pretty cool. They blip out one by one, some taking a direct hit, others barely missed by the Moon’s disk. The whole thing takes roughly a couple of hours. And you can watch it from the safety of your computer: via the Royal Greenwich Observatory blog comes this very slick video of a Pleiadian occultation from December of 2006:

I love how the clouds dance in and out; it adds some drama to the short video. The Moon is actually smaller than it looks here; the overexposure makes it look bigger.

So if you are in the right place to see it, I suggest you take a look. Use binoculars so you can see the fainter stars more easily against the bright Moon. While it’s not as spectacular as an eclipse or meteor shower, it’s still an interesting event.

CATEGORIZED UNDER: Astronomy, Cool stuff
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Comments (27)

  1. “Nuts.”

    My sentiments exactly… Although I suppose any occlusions are a great educational opportunity. Next weekend my daughter and I will be in the back woods of Alabama. No light pollution is always a great time to set up a little camp and just look up!

  2. Adrian

    Great pictures. But I have to quote this:

    “Childs: What do we do now?”
    “MacReady: Why don’t we just wait here for a little while… see what happens…”

  3. Adrian

    Ooops! The comment above was intended for the previous article (Antarctica pictures)

  4. George Kopeliadis

    The Subaru car logo :)

  5. Dr. Phil Plait:

    The Pleaides (sic) are a very tight formation, and only six or seven of the brightest members can be seen to the eye ‚ÄĒ they form a shape that looks a lot like the Little Dipper, and are confused for that constellation by a lot of people.

    Err… Phil, I think you’re confusing the “Little Dipper” with Ursa Minor. The Little Dipper is a junior steel roller coaster located at Memphis Kiddie Park in Brooklyn, Ohio. (Click on my name and see for yourself.)

    Oh, Phil, it’s Pleiades, not “Pleaides”. :-)

  6. RawheaD

    Yeah, these few years are the “in” season for Pleiades occultations. Happens pretty much every 2-3 months. Here’s a shorter timelapse of the event that happened a couple months ago.

    http://www.vimeo.com/1772944

  7. Thanny

    I can see 10 stars in the Pleiades in my sky, when the Moon isn’t out and about.

  8. Click my name for the sound effects to this video… ūüėČ

  9. Heh. I wasn’t sure how to spell it, so I looked it up as Pleaides. I found sites spelling it that way, so ran with it. :) It’s fixed now., thanks.

  10. Chris A.

    @Phil:
    I guess I’m in a quibbling mood today (see my post on the Antarctica pix), but:

    While it’s proper English to refer to the Moon occluding stars or planets, astronomers call it “occulting.” Just curious why you avoided the term.

    Because the angular distance between the northernmost Pleiad (Sterope) and the southernmost (Merope) is just under 37 arcmin, and the maximum angular diameter of the Moon is 33.5. Thus, the Moon can never occult all seven Pleiads in a single occultation pass.

    Oh yeah–you also misspell “Pleiades” throughout. :)

  11. Chris A.

    @Phil:

    Addendum to last post:
    Depending on which of the eight named Pleiads you consider to be the seven sisters (you’d think Atlas would lose out, but it’s brighter than Pleione, Sterope, and Celaeno, so…), the Moon may be able to get “all seven” in one occultation.

    Interestingly, if you’re in just the right spot (near Timbuktu, for example) during this occultation, there will be a moment when the Moon is smack in the middle of the Pleiades, and yet of the brightest seven, only Maia will be occulted. Cool.

  12. Mena

    I’m in suburban Chicago so I’ll have to take everyone’s word for it. Lotsa light pollution here! :^(
    I do have a question though. Does anyone know where I can find a decent star chart online? Everything that I seem to be finding doesn’t let me zoom in and sometimes doesn’t let me move into the area that I want to see and change the date. Having too many stars doesn’t help. I think that I only see 25-33% of what everyone else can see so I can’t get a reference.
    What I’m curious about is that there was a bright object (sorry for not knowing the correct terminology) to the right and kind of above the moon about a week and a half ago and I’d like to be able to find out what it was. It had to be very bright since I could see it, plus it looked extra bright. I’m guessing that it was either a star, Jupiter, or Saturn but would love to know for sure.

  13. Quiet Desperation

    I can see 10 stars in the Pleiades in my sky, when the Moon isn’t out and about.

    Pleia-what?

    Regards,
    A City Dweller

  14. Phil Plait:

    Heh. I wasn’t sure how to spell it, so I looked it up as Pleaides. I found sites spelling it that way, so ran with it. It’s fixed now., thanks.

    You’re welcome, Phil, but you should have checked with Wikipedia. Click on my name for the link.

  15. ERRATUM:

    You’re welcome, Phil, but you should have checked with Wikipedia. Click on my name for the corrected link.

  16. Chris P

    Since pleaisdeades means Subaru in Japanese – I have always been looking for a car shape.

    Now I know better.

  17. magista

    Mena, have you tried YourSky (www.fourmilab.ch/yoursky/)? It lets you change the minimum brightness displayed, and you can turn on and off deep sky objects, names/outlines/borders of constellations and so on. Very handy.

  18. @Mena, I’m guessing you probably saw the moon near Jupiter on November 3, or possibly November 2.

  19. Todd W.

    @Chris P

    Pleiades means Subaru in Japanese? My Japanese is a bit rusty, but I don’t recall ever hearing that.

  20. Mena

    Magista, that’s perfect! Thanks and I have it bookmarked.
    Saganist, that’s about when it was. The only planet that I can identify without a chart right now is Mars (color, obviously) but I’m working to change that. I was guessing Jupiter because of the brightness. I have started downloading Jack Horkheimer’s “Star Gazer” shows online. I have always enjoyed looking at the sky but it’s even more fun now that I’m starting to recognize more constellations too.
    Todd W, my husband also told me that Pleiades is Japanese for the Pleiades. Wikipedia has it as such too, but that’s Wikipedia.

  21. Todd W.

    @Chris P and Mena

    Ahhh…I get it, it’s not that Pleiades is Japanese for Subaru, but rather that Subaru is Japanese for Pleiades. Momentary miscommunication.

  22. ERRATUM:

    The Little Dipper is a junior steel roller coaster located at Memphis Kiddie Park in Brooklyn, Ohio. Click on my name for the now corrected link* to the referred Wikipedia entry.

    *For some reason, the link at my original post above has failed to work. An editing facility would be useful here, Phil.

  23. IVAN3MAN

    NUTS! It still doesn’t work! Oh, I give up, before I lose my mind!

  24. Darth Robo

    This stuff used to be easier to look out for before my old PC went splat. I had a free version of Starry Night which was pretty cool, but now they don’t do the free one no more! :( Got Stellarium now, but it’s not as good.

  25. I will try to watch. Hopefully there will be no clouds…

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