Friday, April 15, 2005

Moon to Hide Supergiant

Moon to Hide Supergiant
by Dave Adalian

A fat full Moon is usually a problem for astronomers, its bright, white light washing fainter objects from the sky. Other times, it’s the star of the show, as it will be the night of May 23-24 when the Moon occults the red supergiant star Antares.

Occultation is a body blocking the view of another more distant body, and a few minutes before midnight on May 23 the Moon will do just that to the ruddy star at the heart of Scorpius. The show, however, starts at sunset.

In Arabic, Antares is called Kalb al Akrab, heart of the scorpion, and staying true to this metaphor, early Muslims named two bright nearby stars Al Niyat, the arteries. The brighter of the two artery stars, Al Niyat (Sigma), will be behind the Moon when it rises. Stargazers with access to a very clear horizon will see this third-magnitude star reemerge from behind the lunar disk at about 8:48.

About then Antares will become visible above the horizon, one and a half degrees or so below the Moon. As the Moon travels west across the sky, it moves east through against the starry background at about half a degree or one full-Moon width an hour, edging ever closer to Antares as midnight approaches.

The Moon appears much brighter and larger than Antares, but this is a mere deception of distance. The Moon is just a quarter million or so miles away and is roughly 2,000 miles wide at its equator. Antares, on the other hand, lies 600 light years away, is 12,000 times brighter than the Sun and measures 745 million miles across. Keep this in mind when the Moon makes supergiant Antares disappear from the sky at four minutes from midnight.

Another thing to keep in mind is Antares advanced age. While it is younger than Sol, our star, it is much larger and brighter, meaning a far shorter lifespan. When the end comes for Antares, it will be with a bang--because of its size, Antares will end life as a supernova.

That explosion could come at anytime, a million years from now or while the Moon is hiding it from view. Likely, Antares will emerge from behind the Moon at 1:12 a.m. no different than when it disappeared. Or, it may reappear as the aftermath of a titanic stellar explosion, outshining all the other stars in our galaxy combined.


This column appeared originally in the Visalia (Calif.) Times-Delta in April 2005.

Friday, April 01, 2005

Return of the King

Return of the King
by Dave Adalian

What’s bigger than a bread box, smaller than the Sun and the brightest thing in the night sky after the Moon these days? It’s 88,000-mile-wide Jupiter!

Those with eyes for the skies may have recognized the bright object dominating the east after sunset the last few weeks as the King of Planets. A fixture in the winter sky for the past few years, Jupiter is making the transition to spring skies as it moves to opposition--when it appears opposite the Sun and is up all night--on Sunday, April 3.

Not to insult the King, but Jupiter really is an old gas bag, and a big one to boot. Jupiter is the largest thing in the Solar System after the Sun, and while it’s only about six times wider than Earth, it would take more than the volume of 1,000 Earths to fill Jupiter’s interior.

Jupiter is so large that it contains more mass than all of the other planets combined, 1.9x10^27 kilograms worth--that’s a 19 followed by 26 zeroes! Astronomers who think they’re cleaver like to say the Solar System is made up of the Sun, Jupiter and assorted rubble.

The Jupiter System itself is fairly rocky, too. When Galileo first viewed Jupiter through a telescope in 1610 he saw just the four bright moons Io, Europa, Ganymede and Callisto. These days, Jupiter’s official NASA moon count is up to 63, with the smallest measuring just three miles across.

Moons aren’t the only thing going around Jupiter. Like Saturn, this gas giant planet also has a set of rings. Jupiter’s rings are much less complex and dimmer, so much so they weren’t discovered until Voyager I visited in 1979.

Like the Sun, the Jupiter is mostly hydrogen, and because of the gravitational pressure of its mass, inside temperatures reach more than 10,000 degrees Fahrenheit. That pressure has caused the formation of a core of metallic hydrogen 6,000 miles below the surface of Jupiter’s atmosphere. Some scientists believe the planet also has a rocky core 10 times the mass of Earth. Others disagree, saying it’s hydrogen all the way through.

In the telescope, dark, cloudy bands reveal themselves on Jupiter’s disk. The four bright Galilean moons are obvious as they dance along night to night, and careful observation reveals the Great Red Spot, a storm three times larger than Earth that has raged since before its discovery in 1664.


This column appeared originally in the Visalia (Calif.) Times-Delta in April 2005.