At the end of the year, we not only reflect back on significant events in our lives but also look forward to the new year with new goals and challenges in mind. In that spirit, I’d like to introduce you to Daniel Fischer’s Ultimate Almanac – rare, unusual and/or spectacular sky events in the 21st century. Fischer lists two events in 2011 worth watching: a close grouping of the bright planets Mercury, Venus, Mars and Jupiter at dawn on May 16 and a possible big show from the Draconid meteor shower on October 8.
Looking further ahead, he notes the much anticipated August 2017 total solar eclipse for North America, the first in the contiguous U.S. since 1979. Has it really been that long? Only seven years later in 2024 we’ll have another, followed by rare pair of back-to-back eclipses in 2044 and 2045. Mars will be a brilliant beacon in the July 2018 summer sky, when it makes its next closest approach to Earth, and the Leonid meteor shower will rage again in 2034. Watch for the return of Halley’s Comet in the summer of ’61!
Astronomers are experts at forecasting future celestial events, because the orbits and motions of the planets, moons and sun are known to great precision. There are occasional adjustments that need to be made, especially for small bodies like comets and asteroids. The jetting of material from a comet caused by heating from the sun can give it a little push and alter its orbit. Asteroid orbits are malleable due to the Yarkovsky Effect. An asteroid’s surface is heated by the sun during the day and cools off during the night. Because of this, the asteroid tends to give off more heat during the afternoon and evening than in the morning. This imbalance causes a tiny acceleration that can build up over millions of years and change the shape of its orbit. Then there’s Jupiter. Its massive gravity can bend an asteroid or comet’s orbit, forcing it into a new one that brings it closer or farther from Earth. Small bodies like these are watched closely for changes, and adjustments are made to ensure that their arrival and departure times are accurate and up to date as they chug their way across the solar system.
The moon will definitely make its appointment with the Pleiades (Seven Sisters) star cluster tonight right on schedule. If you gaze moonward in the early evening, you probably won’t see the cluster because of lunar glare, but any binoculars will readily show the grape-like bunch of stars. As you glance back and forth between the cluster and the moon, you’ll be able to appreciate how much more sky the Pleiades cover compared to the lunar orb. At a casual glance, you’d think the moon would be the larger, but its overwhelming brightness and lack ofÂ good references for size comparison through us off. The moon’s diameter is half a degree – your little finger at arm’s length covers twice that amount or one degree. The brightest part of the cluster spans three full moons or about 1 1/2 degrees. If you slide your binoculars directly below the Pleiades, you’ll bump into Aldebaran and the more spread-out Hyades star cluster, whose apparent size is about five degrees or 10 full moons.
We’re only two nights away from full moon and a total lunar eclipse, when the moon will have moved to the far eastern end of Taurus. All lunar eclipses are fascinating to watch, but this one is interesting on a variety of levels. For one, the eclipsed moon will occupy nearly the same spot as the sun does on the first day of summer. And since a full moon is directly opposite the sun in the sky, it follows that the sun must be parked at the winter solstice position. Moon high – sun low.Â The solstice occurs on December 21, the first day of winter. Nice coincidence and also very rare. The last northern hemisphere winter solstice eclipse was December 21, 1638.
It’ll be 84 years before the next total lunar eclipse happens on the winter solstice (December 21, 2094), but that eclipse won’t be visible from the Western Hemisphere. Sky watchers in Europe, Africa and Asia will get the nod that night. For a North American solstice eclipse, it’s truly a long wait – December 21, 2401! Let’s hope it’s clear this Tuesday morning, eh?