Flashes from the hero’s helmet

The Perseid meteors should be abundant, in the night between August 11 and 12 – Thursday evening into the dark morning hours of Friday morning.

How do you know a luminous streak you see is a Perseid and not some other kind of space-dust?  Because its trail, if you trace it backward, comes from the constellation Perseus.  And where is the constellation Perseus?  It is low over the northeastern horizon as the night begins; it swings slowly south-and-up, aiming to be highest in the south by 6 AM.

In Perseus these particular meteors have their “radiant.”  They come hurtling through interplanetary space on parallel paths, but as they arrive toward you, burning up in the atmosphere, they appear to diverge, to any part of the sky.  They are bits of grit and gravel in a vast diffuse stream, circulating around the Sun in approximately the orbit of the comet (Comet Swift-Tuttle) from which over hundreds of years they have crumbled.

There is detail about the Perseids in the “Meteors” section of Astronomical Calendar 2016.  Here are the few main points for observing.

Go to the darkest and clearest place you can.  Light-pollution smothers all but the few brightest meteors.  (The Flamsteed Astronomy Society won’t try to watch from its base, the Greenwich Observatory, but will Perseid-watch from the grounds of a pub at a village called Cudham, out in the Kent countryside.)

Though it’s summer, dress warmly; maybe take a deck chair and a blanket.  You may find yourself interested enough to stay long into the night.

The Perseids hit Earth roughly from the front.  (Notice the “Earth’s direction of travel” point, below the horizon in the picture.)  This is what makes them swift and bright, but it also means that they are seen most numerously from the front side of the rotating Earth, that is, after midnight.  So you’ll see some Perseids in the hours before midnight, but more if you stay on into the small hours.

It’s a not-perfect year for the Perseids in that the Moon, about 9 days old, doesn’t set till around midnight.  That’s another reason for braving it on into the morning.  (Or getting up at a small hour.)  The moonlight isn’t Full, but it will outcompete some meteors.

How many can you expect to see?  In this respect, 2016 may be an extra good year.  A few Perseids can be seen over a span of more than a month, from about July 17 to August 24; they build up gradually, to a best time covering around 24 hours.  The prediction of the actual peak depends on past counts and on analysis by theorists, and there may be several peaks, caused by parts of the meteor stream that are denser or have been slightly diverted by Jupiter’s gravity.  So there are several answers, ranging from late on Aug. 11 to late on Aug. 12 (by Universal Time).  The number that one person may see per hour around the peak is often between 50 and 90.  This year, it could be higher, for a combination of reasons explained by Joe Rao in an article in this month’s Sky & Telescope.

The group of fairly bright stars making the constellation figure of Perseus is shaped like a sort of forked twig; its northern end represents the hero’s helmet, and that’s about where the radiant is.

This is from the story of the “Royal Family of the Sky” for the  November page of To Know the Stars.  Everyone knows the story of how this Perseus battled the monster (Cetus) and saved the princess (Andromeda).  If the legendary hero, founder of Mycenae and ancestor of Hercules, was a historical person, as the Greeks believed, he may have lived around 1400 or 1300 BC.

Fewer know that there was another Perseus, more than a thousand years later.  He was the last king of Macedonia, which started around 650 BC as a sort of tribal kingdom peripheral to Greece, and rose mightily with Philip and his son Alexander the Great.  Alexander conquered the world between 334 and 331 BC.  The ensuing “Hellenistic” age, and the Macedonian kingdom, lasted until supplanted by the Romans.  And I will end by quoting one of the “Eclipse Stories” from the new edition of The Under-Standing of Eclipses, which as of today I have ready for printing.

168 June 21, lunar total.  The Romans under Lucius Aemilius Paullus defeated the last Macedonian king, Perseus, at the Battle of Pydna, on the coast between Greece and Macedonia.  Gaius Sulpicius Gallus, a scholar and close friend of Paullus, commanded the Second Legion: he predicted that there would be an eclipse of the Moon on the night before the battle.  Paullus had him speak to the troops and explain this so that they would not be frightened.  Nevertheless, Paullus was careful to make sacrifices and wait for favorable omens.  The eclipsed Moon will have been low in the south.  The Macedonians took it as an ill omen, foreboding the death of their king (though Perseus did not die till 166, in exile at Rome).  Gallus on returning to Rome found that his prediction had brought him celebrity; he was elected consul, then played several other political roles, but continued his studies and in his later years turned mainly to astronomy.