Astro Bob: Quadrantid meteor shower, Earth at perihelion, longer days
A trifecta of astronomical events on tap for the first week of the new year.
Every new year brings an astronomical display of fireworks. No, I'm not talking about the spectacular shows from Australia and Hong Kong but the Quadrantid meteor shower.
On Jan. 3-4, the speeding Earth intersects the trail of dust and pebbles dribbled from the asteroid 2003 EH1. Striking the atmosphere at 25 miles per second (40 kilometers per second) transforms the material into flaring meteors in a fascinating, step-wise process.
Heated by air compression, a particle first begins to glow. At the same time, the impact strips away its atoms, which slam into the surrounding air molecules and also make them glow. The result is the sudden appearance of a streak of light called a meteor or shooting star.
The source or "parent" of the Quadrantids, 2003 EH1, is a near-Earth asteroid (NEA) about 2 miles (3 kilometers) across. Unlike some NEAs, it doesn't come close enough to our planet to pose a future hazard.
Because the asteroid may be related to a comet seen in the late 15th century, some astronomers think it could be a comet fragment that has since gone dormant. Either way, Earth plows through material strewn along its orbit every January.
Unlike some meteor showers, the peak of the Quadrantids is very brief, lasting only about six hours. If that narrow interval happens to coincide with the time the shower's radiant stands high in the eastern sky before dawn — and there's no moon to dilute the view — up to 130 meteors per hour might be visible. I've had the pleasure of witnessing this just twice in my life.
Unfortunately, this year's peak occurs around 9 p.m. Tuesday, Jan. 3, when the radiant — the spot in the sky from which the meteors stream — will be below the horizon at that time. That and the bright, waxing gibbous moon will put a serious crimp in this otherwise rich shower for North American viewers.
But don't lose hope. The radiant lies in the defunct constellation of the Mural Quadrant (Quadrans Muralis), an instrument astronomers once used to measure star and planet positions. Nowadays, the Quadrantids fly out of Boötes the Herdsman about 15° or 1 1/2 fists below the Handle of the Big Dipper.
From mid-northern latitudes, the radiant climbs to around 20° high at local midnight on the night of Jan. 3-4 — even earlier if you live farther north. That means some of us might still catch the tail end of the peak. I only wish we could do something about that moon!
Although the radiant rises higher and higher through the night, activity will drop off to a more modest 30 meteors per hour toward dawn. Expect the moon to half that number. To watch, face north or east for the best view — the meteors will shoot from the northeastern sky. Be out anytime from late Tuesday night, Jan. 3, until dawn Jan. 4 and keep the moon at your back. Good luck!
Earth snuggles near the sun
Counter to intuition, Earth is closest to the sun in January and farthest in July. Its distance varies because the planet plies an elliptical path around the sun shaped somewhat like an oval. One end of that ellipse is closest to the sun and the other end farthest. We arrive at the closest point, called perihelion, at 10:17 a.m. Central Standard Time on Wednesday, Jan. 4.
On that date, we'll be 91,403,034 miles (147,098,924 kilometers) from our blazing central star. That's 3.1 million miles closer than aphelion July 6, when Earth arrives at the other end of the ellipse. Being closer means the sun's apparent size is 3% larger than it will be early this summer. And because the nearer a planet gets to the sun, the more quickly it moves, Earth is humping along 2,160 mph faster now than it will be in early July.
If anything, you'd think we'd be warmer in winter and cooler in summer, but the opposite is true because the seasons are primarily controlled by the tilt of Earth's axis. In winter, the northern hemisphere is tipped away from the sun, so days are short, solar heating less and cold temperatures result. In summer we experience just the opposite.
But the southern hemisphere tips toward the sun at perihelion. Is it hotter there than a northern hemisphere summer? No, because the vast amount of ocean in that half the world mitigates the extra bit of energy received from the sun. If it were all rocky continents down under, things might be different.
A couple weeks back, I wrote about day-night length on the winter solstice . Since early December, we've slowly added minutes to the evening end of day even as the sun continued to rise later. But starting around Jan. 6 (find your local sunrise time at timeanddate.com/sun ), sunrise times also begin to reverse.
In Duluth, Minnesota we're currently experiencing our latest sunrises at 7:53 a.m. local time. That flips back to 7:52 a.m. Friday, Jan. 6, adding a full minute of extra daylight to the morning hours. Earlier sunrises combined with later sunsets will soon lead to an obvious lengthening of daylight hours later this month.