Wednesday, October 25, 2006

The Lion, the Moon and Saturn

The Lion, the Moon and Saturn
by Dave Adalian

Starting before dawn on Monday morning, the Moon will enter the belly of the beast.

In the early morning, around an hour or so before sunrise, the slender crescent of a waning moon will lie due east, sitting like a cosmic ball of yarn between the paws of Leo the Lion.

But, it won’t be alone. Just below and the to the right of the Moon will be the bright, yellow ringed planet Saturn, making it a cinch to find this second largest of the eight planets.

While it will seem the Moon and Saturn are so close they could reach out and touch one another, in reality the Moon is just 220,000 or so miles from Earth, while Saturn is more than 900 million miles away at present. And, while Saturn, a simple pinprick in the sky, seems much smaller than our 2,000-mile-wide Moon, it is actually 75,000 miles across.

In fact, Saturn’s rings are the largest structure in the Solar System besides the Sun itself. Measured side to side, Saturn’s ring system is an impressive 155,000 miles wide.

On Tuesday morning, a still thinner Moon will head deeper into Leo, sitting just below the lion’s brightest star, Regulus. The word Regulus is Latin for “the prince,” and is sometimes referred to as Cor Leonis, or the heart of the lion.

Regulus is a young, fast spinning star, making a complete revolution about every 16 hours, a spin so quick it makes the star bulge in the middle. And, while Regulus is a very bright first-magnitude star, it is actually 77.5 light years away.

By Wednesday morning, the Moon will have moved on again, its crescent growing smaller still as it leaves Leo and passes just to the right of the brightest star in Leo’s tail, Denebola, a name which means “tail of the lion” in the original Arabic.

While second-magnitude Denebola is not nearly as bright as Regulus, it is actually larger at 1.6 million miles wide compared to Regulus’ 1.4 million mile girth. It’s also closer, less than half as far away at 36 light years.

If Denebola is closer and bigger than Regulus, why does Regulus shine more brightly? Simply because it is hotter, its higher temperature making it shine 350 times brighter than our Sun. Cooler Denebola is a mere 12 times brighter than 865,000-mile-wide Sol.


Join the Tulare Astronomical Association for a look at the stars of autumn Friday, 7:30 to 9:30 p.m., at the Arthur L. Purcell Observatory, 9242 Ave. 182, south of Tulare and 2.1 miles west of Highway 99. Information and directions:


This column originally appeared in the Visalia (Calif.) Times-Delta and Tulare (Calif.) Advance-Register on Oct. 12, 2006.

Don’t Mourn for Pluto

Don’t Mourn for Pluto
by Dave Adalian

After 76 years as the Solar System’s ninth planet, Pluto suddenly finds himself all alone out in the cold.

Of course, he’s probably used to that by now.

At a meeting of the International Astronomical Union last month, Pluto was stripped of its status and reclassified as a “dwarf.”

The poor little guy. But, does he deserve it?

Truth be told, Pluto is a whole lot different than his Sun-hugging cousins.

First off, he’s tiny, about half the diameter of Mercury, smallest of the rocky inner planets, smaller than many of the other planets’ moons, including Earth’s. His size really isn’t all that odd, except Pluto lives in the land of the gas giants, the smallest of which, Neptune, could hold 60 Earths if it were hollow.

Making Pluto even odder, his axis is inclined so much his north pole points at the Sun. But, he’s not alone here. Uranus, too is tilted on its side.

Also, the largest of Pluto’s three moons, Charon, is almost half as big as he is, making them a double system in the minds of some astronomers. And again, he’s not alone in this. Earth and the Moon are somewhat similar in size and considered a double planet in some circles.

So, what’s the fuss?

Well, the IAU’s new definition of a planet says planets have orbit the Sun, have to be round, can’t orbit another planet and have to clear their orbit of other objects. It’s that last item that’s gotten Pluto in hot water.

Pluto takes a unique path around the Sun. Not only is his orbit tilted, taking it up and down like a horse on a merry-go-round, that orbit is also highly eccentric, sometimes taking the small body inside the orbit of Neptune.

Pluto doesn’t move like the other planets do because it is one of the largest objects in the Kuiper Belt, and since there are thousands of other Kuiper Belt objects sharing Pluto’s orbit, he just doesn’t fit the IAU’s new definition. So, out he goes.

In general, astronomers aren’t an excitable bunch, but the decision last month has professional stargazers around the world crying foul. The vote, held on the last day of the IAU’s meeting, only included the opinion of a handful of the body’s 10,000 or so members, many of whom are calling for another vote on the matter.

So, Pluto might regain his status as a planet the next time the IAU comes together. Either way, Pluto probably doesn’t much care what people on a planet so far away it can’t even be seen from where he sits call him.


This column originally appeared in the Visalia (Calif.) Times-Delta and Tulare (Calif.) Advance-Register on Sept. 14, 2006.

Planets Dance in the Predawn Light

Planets Dance in the Predawn Light
by Dave Adalian

Early risers and those who like to stay up until dawn will be treated to a planetary dance if they’ll look to the east before first light all next week.

On Sunday morning just before the Sun rises three planets will hover just above the eastern horizon. Brightest and easiest to find of the trio will be Earth’s twin sister Venus.

This 8,000-mile-wide orb is about the same size as our own planet, but covered with a planet-wide haze that reflects back much of the light that strikes it, making it one of the most dazzling sights in the night sky.

Closer to the horizon and to the left of Venus will be a close pairing of Mercury and Saturn. On Sunday morning, Mercury will sit about a degree above the ringed planet and both will be very close to the horizon. Twenty-four hours later, the pair will have switched positions, with swift-footed 3,000-mile-wide Mercury moving so quickly toward the Sun it will appear about one degree below slower-moving Saturn.
Also joining the dance on Monday morning will be a very slender crescent moon sitting above the planetary trio. The Moon will be even thinner still, as thin as you are ever likely to see it on the last day of its 28-day cycle, on Tuesday morning when it floats near Saturn’s left-hand side.
For a striking example of what a difference distance makes for planetary viewing, remember that our moon is just 850 miles more narrow than faraway Mercury but appears roughly 166 times larger to the naked eye.
By Wednesday morning, Venus and 75,000-mile-wide Saturn will be all alone in the eastern sky with Mercury lost in the wash of predawn brightening.
Their other dance partners now gone, Venus and Saturn will go it alone over the next several mornings while Venus makes its way closer to Saturn and sunup each day.
On Tuesday, with the Moon close at hand, Saturn and Venus were some 5 degrees apart, by Friday the gap will have narrowed to less than 2 degrees, or about four times the width of the full moon.
The gap will be at its smallest over the weekend when Venus will be less than one degree above Saturn, and the final move of the celestial cotillion will come on Sunday morning when the two change position, with Saturn now less than a degree above Venus.
Join the Tulare Astronomical Association for its monthly public star party this Friday, 9-11 p.m., at the Arthur L. Purcell Observatory, 9242 Ave. 184, south of Tulare and 2.1 miles west of Highway 99. Information and direction:


This column originally appeared in the Visalia (Calif.) Times-Delta and Tulare (Calif.) Advance-Register on Aug. 17, 2006.