For the Birds Radio Program: Mars
This week Mars is as close to earth as it has ever been or will be within our lifetimes, right when migration is reaching a peak.
This summer, Mars is as close to earth as it has ever been during our lifetimes. On August 27, 2003, it will be 34.65 million miles away from earth. Six months ago, it was five times that distance from us. After Wednesday, it will be very slowly drawing away again, but still huge for several weeks, and rising earlier and earlier so more of us can enjoy the spectacle.
Of course, every two years or so our planet and Mars are both in what astronomers call ‘perihelic opposition, ‘ meaning the two planets are both in the general area where their elliptical orbits are closest together. And in the coming years, there will be more opportunities to see Mars this close again. But right now, that brilliant red planet glowing in the southern sky is the most brilliant and huge that it’s been in 50,000 years.
So this week millions of people will be looking at Mars, right when songbirds are starting to migrate. Mars is now rising fairly early in the evening, and so in some areas it’s possible to see it low on the southeastern horizon right as nighthawks are winging their way overhead. There’s no way I could keep my eyes on a planet, even a glowing red one, when nighthawks were flying. But as Mars gets higher in the sky, it grows too dark to see even nighthawks, and I find it easier to keep my eyes on the fourth rock from the sun. But even as I watch Mars, my ears are perked up, listening for nocturnal migrants. So far all I’ve been hearing as I look up at Mars have been crickets and a couple of robins stirring in their sleep, but some nights, especially close to midnight during the coming weeks, warblers and thrushes will be making distinctive little notes overhead. These nocturnal migrants use the stars to find their way. They’re definitely not following Mars—planets are too restless, wandering here and there like celestial birds. From the time real baby birds are in the nest, when they peek up at the sky at nighttime, they notice that the star pattern changes from hour to hour. And they notice that one star remains fixed, with the other stars rotating around it— Polaris. Birds know instinctively that they can count on Polaris. Their first fall, young nocturnal migrants set their course directly away from Polaris, and that sends them south. Most migrants do have tiny particles of magnetite in their brains, but they probably don’t use this internal compass except when the stars are obscured by clouds.
When Indigo Buntings and White-crowned Sparrows were experimentally raised in a planetarium, researchers made the projected stars rotate around Betelgeuse instead of Polaris, at migration time the birds set their course straight away from Betelgeuse. And when patches of stars are hidden in a planetarium, the birds recognize simple wedges of stars, so even if the north star is obscured, they can use the stars around it to navigate. To keep from bonking into one another, they make special little calls, and although these sounds are tricky to identify, hearing them tells us about all the travelers passing over our heads.
Daylength right now is similar to what it was in spring, which triggers in some birds a resurgence of song. Owls in particular spend some time hooting in late August and September, so right when people are outdoors looking at Mars, Barred and Great Horned Owls may be calling. All in all, Mars is a pretty quiet planet, even at close range, but watching it can be as rewarding to our ears as our eyes, if only we pay attention.