Stones the size of goose eggs

May a happy year start for you tomorrow! And may no stones fall from the sky on your head!

The first of the major annual meteor showers should be at its peak in the night between January 2 and 3, mostly after midnight.

See the end note about enlarging these diagrams.

Here you see the scene at midnight, soon after the rising of the radiant – the place in the sky from which the “shooting stars” in their parallel paths appear to fly out. As the night goes on, the radiant will slope up, parallel to the celestial equator, so that it will be highest before dawn.

Meteor showers have names derived from the constellations where their radiants are. In this one case, the constellation is a disused one:, Quadrans Muralis , the “wall quadrant” (an instrument for measuring the positions of stars)), which in old star maps covered an area now assigned to Boötes. If you see, in any part of the sky, a luminous streak that can be traced back to this area near the end star of the Big Dipper, it’s a Quadrantid and not a sporadic meteor.

Showers happen when Earth passes through a stream of particles that follow roughly the orbit of a body from which they were shed, perhaps centuries ago. For most streams the parent body is a comet. The Quadrantids’ parent was long unknown, but in 2003 Peter Jenniskens suggested, from similarity of orbits, that it was asteroid 2003 EH1, discovered in March of that year; and that this might be identified also with a comet recorded by Chinese, Korean, and Japanese observers in December of 1490 and now designated C/1490 Y1.

In March or April 1490, stones up to the size of goose eggs fell from the sky like rain on a place in north-west China, killing more than 10,000 people. There is no certainty whether this Ch’ing-Yang Event consisted of hailstones or, like the Tunguska event of 1908 June 30, was an object from space that exploded  in the atmosphere; there is a temptation to connect it with the comet, but the difference of eight or nine months makes that unlikely.

‘Twould have been worse if they were swan eggs.

Geese and swans mingling amicably on the river shore at Isleworth

Asteroids are solid, like tiny planets; comets are small clouds of solids held together by ice which can be vaporized by sunlight, but some may have solid cores which are left looking like asteroids. The orbit of the 1490 comet is given as parabolic (eccentricity 1), but, if the connection with the later phenomena is valid, it must have been of shorter period; it may have disintegrated a century or so later, giving rise to the meteor stream, the asteroid being the remaining core. The great Geminid shower of December is the other one associated with an asteroid, though in a much smaller orbit.

The reason why the Quadrantids start coming into view toward midnight is that the stream meets Earth’s front or morning side. The radiant is well north of, and slightly in front of, the direction in which Earth is traveling at this time, which you can see marked in our sky scene above.

In this space view

which is from ecliptic north, the broad arrow shows Earth’s flight along its orbit in 3 minutes, and an arrow above its equator shows its rotation in 3 hours.  The time of the picture is 12 UT, which is 7 AM in the Eastern time zone of North America; earlier in the night for zones to the west.

The dots represent only the thread of the meteor stream that happens to be overhead. Meteor streams are vastly wider than the Earth.

And as the “Moon overhead” line shows, Moon-dazzle is not a problem for the shower this year. The Moon is almost in the same direction as the Sun, having passed through its new phase between us and the Sun late on January 2.

So you may see enough Quadrantids, these flashes of incandescence with a mysterious history behind them. Their ZHR, or zenithal hourly rate, is estimated as 120. But this means the average number that an alert observer might count if the radiant is overhead and sky conditions are perfect. For the first of those you’d have to be in Canada and for the second you’d have to have January weather a lot better than I’ve been seeing! Wrap up warmly and take a hot toddy out there.

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ILLUSTRATIONS in these posts are made with precision but have to be inserted in another format.  You may be able to enlarge them on your monitor.  One way: right-click, and choose “View image”, then enlarge.  Or choose “Copy image”, then put it on your desktop, then open it.  On an iPad or phone, use the finger gesture that enlarges (spreading with two fingers, or tapping and dragging with three fingers).  Other methods have been suggested, such as dragging the image to the desktop and opening it in other ways.

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