A Line of Planets

For a few days in mid-December 2004, the planets Mercury through Pluto are
arranged from east to west in Earth’s sky in the same order that they’re
positioned outward from the Sun. This situation begins when Mercury passes
inferior conjunction (between the Sun and Earth) on December 10th, and it
ends when Pluto leaves the evening sky on the 13th. Only the planets Venus
through Saturn are observable with the unaided eye on these nights, with
Uranus and Neptune visible in binoculars and telescopes. Both Mercury and
Pluto are hidden in the Sun’s glare.

Such a lineup is rarer than a transit of Venus. Apart from a similar brief
interval in November 2002, the planets have not been arrayed in their
natural order westward from the Sun since before the invention of the
telescope, and they won’t be again for at least four centuries.

A line of planets stretching to the east of the Sun is equally rare. This
occurred in late February and March 1801, and it won’t happen again until
April 2333!

December Meteors

Immediately after the planet parade, an old, reliable meteor shower heads
our way. The annual Geminids should reach peak activity late on the night
of December 13-14 (late Monday night and early Tuesday morning).

Along with the better-known Perseids of August, the Geminids are the
strongest of the reliable annual meteor showers that hardly change from
year to year. SKY & TELESCOPE magazine predicts that late on the peak
night, you might see a “shooting star” every few minutes on average.

The time to watch will be anytime from about 10 p.m. Monday evening,
December 13th, until the first light of dawn on Tuesday morning. This year
there’s no glare from moonlight to worry about, because the Moon is a
two-day-old crescent that sets early Monday evening.

You’ll need no equipment but your eyes. Find a dark spot with an open view
straight up and no bright lights nearby to spoil your night vision. Bring
a reclining lawn chair, bundle up warmly, and bring a sleeping bag; clear
nights get very cold.

“Just lie back and watch the stars,” says SKY & TELESCOPE senior editor
Alan MacRobert. “Relax and let your eyes adapt to the dark. Be patient.”

With a little luck you’ll see a Geminid every few minutes on average.
They’ll appear as often as once a minute if you have a dark sky far from
the light pollution (skyglow) that hangs above populated areas.

Faint Geminids appear as tiny, quick streaks. Occasional brighter ones,
often appearing yellow, may sail across the heavens for several seconds,
leaving brief trains of glowing smoke.

If you trace each meteor’s direction of flight backward far enough across
the sky, you’ll find that the imaginary line you’re drawing crosses a spot
in the constellation Gemini near the stars Pollux and Castor.

This spot is the shower’s radiant, the perspective point from which all
the Geminids would appear to come if you could see them approaching from
the far distance. The radiant is well up in the east by 10 p.m., nearly
overhead around 2 a.m., and high in the west by the first light of dawn.
But you don’t have to look there. Just watch whatever part of your sky
is darkest.

The Geminid shower is active for several days, not just on its peak night.
You may see a few meteors for two or three nights beforehand and one night

The Geminid meteoroids (particles) are tiny, sand-grain- to pea-size bits
of rocky debris that have been shed by a small asteroid named Phaethon.
Over the centuries these bits have spread all along the asteroid’s orbit
to form a sparse, moving “river of rubble” hundreds of millions of miles
long. Earth’s own annual orbit around the Sun carries us through this
stream of particles every mid-December.

The particles are traveling 22 miles per second with respect to Earth at
the place where we encounter them. So when one of them strikes the Earth’s
upper atmosphere (about 50 to 80 miles up), air friction vaporizes it in a
quick, white-hot streak.

Amateur meteor watchers who have dark skies and are willing to follow
careful guidelines can carry out scientifically valuable meteor counts, as
described on SKY & TELESCOPE’s Web site:


* * * * *

SKY & TELESCOPE is pleased to make the two broadcast-quality animations
and one publication-quality illustration available to the news media.
Permission is granted for one-time, nonexclusive use in print and
broadcast media, as long as appropriate credits (as noted in each caption)
are included. Web publication must include a link to SkyandTelescope.com.
To download the graphics and read the captions, see the online version of
this press release:


* * * * *

Sky Publishing Corp. was founded in 1941 by Charles A. Federer Jr. and
Helen Spence Federer, the original editors of SKY & TELESCOPE magazine.
The company’s headquarters are in Cambridge, Massachusetts, near the
Harvard-Smithsonian Center for Astrophysics. In addition to SKY &
TELESCOPE and SkyandTelescope.com, the company publishes NIGHT SKY
magazine (a bimonthly for beginners with a Web site at NightSkyMag.com),
two annuals (BEAUTIFUL UNIVERSE and SKYWATCH), as well as books, star
atlases, posters, prints, globes, and other fine astronomy products.