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The ancient Chinese story of the Weaver Girl (Altair) and the Cowherd (Vega) tell of starcrossed lovers who are only allowed to meet once a year on the 7th day of the 7th (Chinese) lunar month, roughly around early August, when magpies form a bridge across the silver river (the Milky Way.) This is celebrated in the Qixi festival in China (August 9th in 2016.)

Because of the timing, I'm suspicious that the magpies represent the Perseid meteor shower (August 12th in 2016.) But I just got my first planisphere, and Altair and Vega are pretty far away from Perseus (although Perseus is still on the Milky Way.) The Wiki article and others that I've looked into on Weaver Girl and Cowherd does not connect the magpies to any meteor shower.

But the Weaver Girl and Cowherd story is pretty old - up to 2600 years according to Wikipedia. I don't think the Perseids have always been in Perseus due to the precession of the equinox, but 2600 years ago maybe the "Perseid" shower was closer to the southern triangle, or is that too far away to be explained only by precession of the equinox?

I'm very new to astronomy and I'm not Chinese, but I love this story and I'm looking for more information.

Thanks!

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  • $\begingroup$ I don't think the timing of the shower has changed- WIki is convincing that the Perseids have been known as the Tears of St. Lawrence since ~400 C.E. because it coincides with St. Lawrence's Feast Day, August 10th, around the peak of the Perseids. I also don't think that the Weaver Girl and Cowherd story reference the Lyrid meteor shower in mid-April, as the timing is convincing to be around August 8th. $\endgroup$ – MAS Jun 5 '16 at 13:40
  • $\begingroup$ I have seen a planisphere online suggesting that where Perseus is now in the night sky, is roughly where Cassiopeia was 2600 years ago - only a little closer to Vega. Chinese astronomy / astrology was pretty advanced 2600 years ago, but I suspect that sometime around 2600 years ago Swift-Tuttle was at perigee, a high rate of meteors rained down, some Chinese storyteller looked up, and saw showers somewhat close to the brightest star in the summer sky, and connected the Weaver Girl (Altair) and Cowherd (Vega) to magpies (Perseid meteors.) $\endgroup$ – MAS Jun 5 '16 at 13:53
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There is a discussion of this at http://cosmoquest.org/forum/archive/index.php/t-107733.html

In summary, the perseids occur on the same date of the sidereal year, which differs from the tropical year due to precession. This causes a change of about one day in 70 years to the date of a meteor shower. 2600 years causes a change of about 37 days compared to the current calendar: The perseids would be at the end of June or the start of July, in the Gregorian calendar.

However the Chinese Calendar isn't Gregorian: it is Lunisolar, based on astronomical observation of the solstice and the months, with intercalendary months added as required. The date of the the Qixi festival varies from year to year. Meteor showers were noted in China (see my link below), and may be incorporated into myth, but that would be speculation.

The position of the radiant would move with the stars, so the radiant would still be in Perseus 2600 years ago, and not near Vega. But Perseus (and Vega) would be in a slightly different position in the sky.

You may be interested in article about Early meteor shower observations in Japan, Korea and China

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  • $\begingroup$ Thanks! I retract my comment that the tears of St. Lawrence date to the early middle-ages, because I have seen some other well-researched analysis challenging this. I also understand now the point that cometary debris also precesses with the equinoxes (hence meteor showers precess.) $\endgroup$ – MAS Jun 8 '16 at 23:29
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Okay, this turned out to be quite a long answer describing a few arguments I've com up with. The short answer is: maybe, maybe not, but I think it's possible. There are arguments to be made for either side of this discussion, and I don't think you you can ever be absolutely sure unless you find an expert on both astronomy and Chinese folk tales (which I don't claim to be), or invent a time machine to go back 2600 years and check for yourself.

The most obvious argument to be made in favor of the hypothesis that these magpies are the Perseid meteor shower, is that folk tales referencing stars are very likely to be based on astronomical occurrences during that period (such as a meteor shower, perhaps).

The (in my mind) most obvious argument against your hypothesis is what you suggest yourself: Perseus is quite far away from Vega and Altair. However, Perseus is the radiant of the shower, which means that all perseids will appear to come out of Perseus. Because of this, it is perfectly possible for a lot of perseids to appear between Altair and Vega, parallel to the Milky Way. It is, however, impossible for them to go from Vega to Altair, or vice versa, since they wouldn't come out of Perseus anymore.

You suggest that this could be explained by the precession of the equinox, but a quick lookup on Stellarium (which is a great (and free) tool if you're into astronomy) tells me that even 2600 years ago Perseus was quite far away from Vega and Altair (actually, that's quite obvious, since the precession of the equinox causes stars to move relative to the extension of the north pole, but not relative to each other, as far as I know).

Another argument to be made against this hypothesis is that the perseids are by far not spectacular enough to be seen as a bridge over the Milky Way, even when they all appear in the required spot. During the yearly peak of the perseids, you are expected to see about 1-2 meteors per minute, which can be noticeable at best. This argument is then countered by the fact that the ZHR (how much meteor you see per hour) is not the same every year, but can peak on years when Earth passes through a fresh dust cloud left behind by the comet that causes the shower (which, in this case, is the comet Swift-Tuttle, if you're interested). Therefore, it is perfectly possible that the perseid meteor shower was extremely active 2600 years ago, causing the creation of this story. Such peaks are somewhat rare, but not too rare for this hypothesis to actually make sense (in fact, we will be seeing such a peak in 2028).

The fact that the dates of the festival and the peak of the perseids are a few days apart and not exactly the same is not quite an argument against your hypothesis, since it is perfectly possible for the date of the festival to have moved slightly due to differences between the (old) Chinese and Western calendars. I'm not an expert on calendars, however, so I can't say that for sure.

Given all these uncertainties, your hypothesis (along with what you mentioned yourself in your own comments) seems plausible, apart from one thing: we don't know whether Swift-Tuttle was already active 2600 years ago. If it wasn't, the perseid meteor shower obviously did not exist (note that comets don't exist forever: some gravitational variation causes them to exit the Oort cloud and enter the solar system). We don't know when exactly Swift-Tuttle started being a comet.

That is only a weak argument, however, and when it comes to astromical hypotheses, the most convincing argument is usually a principle which is referred to as Ockham's razor: if given multiple explanations, choose the one that requires the least amount of assumptions (or the most plausible ones).

Personally, since the date of creation (2600 years ago) is very vague (the uncertainty on this must be at least a hundred years), I think it is perfectly possible to assume that the perseids peaked somewhere during that period, causing the creation of this story.

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  • $\begingroup$ Thanks for the detailed answer! I will check out Stellarium. As I understand, the Perseids occur when the earth crosses the pane of Swift-Tuttle debris, around Aug. 10th. Currently (J2000), that crossing is centered fixed in the celestial sphere around Perseus (whose nearest star is of course many parsecs away.) But 2600 years ago, the celestial north pole was different, and the same point in the plane of the earth's orbit is different relative to the celestial sphere. I agree, I don't think near enough to Vega, though. Either way I'm excited for this coming August. $\endgroup$ – MAS Jun 5 '16 at 16:24
  • $\begingroup$ I'll have to read up on the life of a comet. I wondered if they were either "annual" - they wake up out of the Oort, and either slam into the sun, or into, say, Jupiter, on their first trek, or "perrenial," meaning if they survive one trip around the sun then they can survive many, many more. Ockham's razor works both ways - if, for example, an ancient, 3000 year-old culture celebrated meteor showers radiating from near Leo around mid-November, that would "prove" that Temple-Tutlte has been active for at least 3000 years. A fun thing to think about nonetheless! $\endgroup$ – MAS Jun 5 '16 at 16:42

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