February 2000 Sky from Keeble Observatory
Is the sky falling? A recent news item from Spain finds local authorities puzzling over mysterious, soccer-ball sized ice fragments which reportedly fell there. One woman claims to have been hit on the shoulder by a chunk of ice weighing about 10 pounds. A man claims to have narrowly averted a serious automobile accident, when his car was struck by another one of these ice balls. What’s going on? Past episodes of ice from the sky have been linked to aircraft venting their waste tanks, but these don’t appear to have such an origin. Some have suggested that these might be comet fragments, but that also seems highly unlikely. There is a type of icy precipitation, known as graupel, which sometimes grows to large size. It is sometimes known as "soft hail" – but it is not clear whether these ice balls qualify under that definition, either. A couple of them have been identified as hoaxes, originating in a restaurant freezer. What about the others? The ice is being tested – if anything more is said, we’ll let you know.
Preliminary results from a neat project – that’s N.E.A.T. (which stands for Near Earth Asteroid Tracking) – suggest that we can breathe a little easier. 1998 movies (in particular Armageddon and Deep Impact) would have us believe that the threat of annihilation by killer asteroids and comets is real. Actually, it is real! However, we need some perspective, and that’s where NEAT comes in. This project is conducting a survey and census of Near Earth Asteroids, objects up to 6 kilometers in size, whose orbits bring them occasionally near the Earth. It had been estimated that there could be several thousand such objects, giving us roughly one chance in 20,000 of suffering a catastrophic collision in any given year.. Such an object excavated the Chesapeake Bay several million years ago, albeit one on the large end of the scale. An even bigger object hit near what is now the Yucatan Peninsula some 65 million years ago, ultimately bringing the dinosaurs to extinction (and clearing the way for the rise of mammals like us!). In 1908 a rocky asteroid about 100 meters across exploded over Siberia, leveling many square miles of tundra in what has come to be known as the Tunguska event. The good news from this survey? There are apparently only about 1000 objects of this size in earth-crossing orbits. So we can relax a bit. On the other hand …
On the 19th of January a meteor exploded over the Alaska-Yukon border. Visible in broad daylight, and described as appearing something like green "sheet lightning," this smallish extraterrestrial visitor was accompanied by a sonic boom of sufficient intensity to register on several seismographs. It is not yet known if any fragments hit the ground. Nor do we yet know if this was a rocky meteor or a small comet fragment.
Perhaps Chicken Little was right!
Lunar phases for February: New Moon on the 5th at 8:03 am; First Quarter on the 12th at 6:21 pm; Full Moon on the 19th at 11:27 am; Last Quarter on the 26th at 10:53 pm.
For a while this month, there will be four planets visible in the evening sky! As soon as it gets dark, look to the west to find Mercury. At the beginning of the month, Mars lies about 30 degrees above and to the left. By mid-month, before Mercury disappears into the glare of the Sun, Mars will close to about 20 degrees from Mercury. Jupiter and Saturn are bright to the southwest. Venus dominates the southeast horizon at dawn. On the 2nd, the old Moon will pass close by Venus.
Our mid-month look overhead at about 9:00 pm finds Castor and Pollux nearing zenith and a bit to the east. To the west of zenith are the more widely spaced bright stars in the constellation Auriga – Capella and Elnath. On a clear night, binoculars may reveal the ghostly Crab Nebula just to the south of Elnath. This is the remnant of a star which suffered a violent, catastrophic explosion at the end of its lifetime. The supernova was visible in 1054 AD, and was recorded as a "guest star" by the Chinese. There are even rock paintings in the desert southwest which show that native Americans saw it. It was not, however, reported in Europe – perhaps that’s why they call them the Dark Ages! At the heart of the Crab, invisible to all but the new x-ray telescope known as Chandra, is a spinning neutron star which drives a pulsar, flashing on and off 30 times each second across the spectrum. A neutron star is the remnant of a massive star, crushed by its own gravity into a ball which would fit neatly between Ashland and downtown Richmond.
The dominant constellation to the south is the easily recognized Orion. The red giant Betelguese marks the Hunter’s right shoulder (left on the sky) with Rigel at his left knee. Behind Orion is the brightest star visible from Earth – blue-white Sirius in the constellation Canis Major. Sirius is actually a binary, but its white dwarf companion is too faint to be seen without a large telescope. (A white dwarf is the remnant of a star much like the Sun, after it has used up its nuclear fuel, converting the bulk of its hydrogen to helium and maybe its helium into carbon. It is not massive enough to trigger further fusion reactions, so it shrinks to a hot ball about the size of the Earth, yet still as massive as the Sun.)
To the west, look for Leo, with the bright star Regulus marking the heart of the lion. Also in Leo, look with binoculars for the giant elliptical galaxy M 105. The M stands for Messier, who catalogued a number of galaxies and nebulae to avoid mistaking them for comets. This galaxy is item #105 in that catalog. The Crab Nebula, mentioned above, is also known as M 1 – the first item in that catalog.
The Milky Way divides the overhead sky, running roughly northwest to southeast. This faint ribbon of light is actually the collective glow of billions of stars in the disk of our home Galaxy.