As you may have read in this month’s companion article “A Space for Birds,” the migration of our feathered friends back to the region is both an occasion for joy in itself and a testament to nature’s resilience. But what does astronomy have to do with birds, you ask? Read on!
Before continuing, I should mention key events to watch for in this month’s night sky. Most striking, to my mind at least, is the phenomenon known as earthshine, which we will see on the face of the moon on the night of April 15-16. Also called “Da Vinci glow” after the first person, Leonardo Da Vinci of course, to explain it, earthshine occurs when the shadowy side of the waxing moon is illuminated by sunlight that has bounced from the earth to the moon, then back to earth. That’s right: sometimes you can see the dark moon shining with the soft glow of the earth rather than the more familiar opposite. Amazing!
The second notable astronomical event of April is the Lyrids Meteor Shower, which peaks on the night of April 21-22. The Lyrids, which have been known for over 2,500 years, are caused by a comet that every 415 years thoughtfully deposits a trail of icy debris in the solar wind to burn up in the atmosphere and flash in our April skies. The Lyrids are of moderate intensity but have been known to produce fireballs. It’s well worth the price of admission.
That price is simply to head outside in the wee, probably chilly, hours on the night of April 21 and look south-east and near the zenith. Look for a giant bird, Cygnus, the Swan, and beside it the bright star Vega. Just to the right is the radian for the Lyrids — the point that meteors will appear to streak away from. Naked eyes will do just fine if your skies are not too light-polluted or washed out by the moon.
Speaking of swans in space, here is a fact-fireball that streaked across my skies this month. It has to do with that feathery migration you read about in that other article.
For centuries, scientists have tried to explain how birds migrate thousands of kilometers, sometimes, without aid of GPS, maps, or rolling down the window to ask pedestrians for directions. The Arctic Tern, for example, completes an annual round trip of over 20,000 kilometers. But how?
The answer is complex: birds seem to use a combination of dead reckoning, navigation by the sun and/or stars, and memories of significant landmarks. But they have another trick, too, lately discovered, that is truly astonishing.
The science is still evolving, but these are the basics. Deep in the eyes of some birds there is a protein, Cry4, whose molecules contain an imbalance of electrons that results in adjacent Cry4 molecules being weakly attracted to one another. This weak bond is broken when a photon — a bit of light streaming into the bird’s eye — whacks into the pair like a tiny hammer. The molecules separate and then either re-connect or connect with other molecules. Whether they reconnect or not changes the way that blue light is transmitted along the optic nerve of the bird. And what affects the chance of molecules re-connecting? Location in the earth’s magnetic field!
Deep within the earth lies a solid core of iron and nickel with a molten outer core in constant churn around it. This churning creates a gigantic magnetic field that projects far into space in invisible filaments, or field lines, that wrap around the earth in onion-like layers and shield us from the sun’s powerful radiation. Without that magnetic shield, the only style of bacon you could get would be extra-crispy. So, three cheers for magnetism!
And a fourth cheer for the Barn Swallow, Oriole, or Canada Goose that wings its way toward us from Central America or the southern US with one eye on Millbrook and the other on Cygnus, the swan, gliding along invisible field lines under the silent, soft glow of earthshine.
Stargazing by Dennis Vanderspek