Saturday: Today is the day we celebrate the anniversary of something new – a new classification of celestial objects. Giuseppe Piazzi discovered Ceres [pronounced sear’-ease], the first of what are now called “asteroids”, on January 1, 1801. Ceres is the largest asteroid in the belt between Mars and Jupiter. At first, Piazzi thought it was a star that didn’t show up on his charts. But, he noted its position changed with respect to the background stars from night to night. This indicated to him that it had to be orbiting the Sun. In August of 2006, Ceres got promoted to the status of “dwarf planet” by the International Astronomical Union.
Has it been tough to wake up this past week? It should have been because the sunrise has been getting a little later since summer started. I know. I know. December 22 was the shortest day of the year. But, because the Earth’s orbit around the Sun is elliptical and not circular, the Earth does not travel at a constant speed. It moves faster when it is closer to the Sun and slower when it is farther away. This leads to the latest sunrise occurring in early January, tomorrow for 2011, and the earliest sunset occurring in early December, not on the first day of winter, the shortest day of the year. On the first day of winter, however, the interval between sunrise and sunset is the shortest.
Sunday: Today’s weather forecast: showers. Meteor showers, that is. The Quadrantid meteor shower peaks over the next two nights. Meteor showers are named after the constellation from which the meteors appear to originate. That makes this shower mysterious because there isn’t any constellation with this name now. The shower was named after Quadrans Muralis, an obsolete constellation found in some early 19th century star atlases. These meteors appear to come from a point in the modern constellation Draco the dragon. This point is about three fists held upright and at arm’s length above the northeast horizon at 1 a.m. In good years, careful observers can spot about 100 meteors per hour. Fortunately, 2011 is going to be a good year because the moon will be new during the peak nights meaning less ambient light to obscure the dimmer meteors. Meteors are tiny rocks that hit the Earth and burn up in the atmosphere. Most meteors are associated with the path of a comet. This shower consists of the debris from an asteroid discovered in 2003. Keeping with the comet-origin paradigm, astronomers think the asteroid is actually an “extinct” comet, a comet that lost all of its ice as it passed by the Sun during its many orbits.
Monday: If the Sun looks big today, your eyes are not playing tricks on you. The Earth is at perihelion at about 11 a.m. If you dig out your Greek language textbook, you’ll see that peri- means “in close proximity” and helios means “Sun”. So, perihelion is when an object is closest to the Sun in its orbit, about 1.5 million miles closer than its average distance of 93 million miles. Since it is winter in the Northern Hemisphere now, the seasonal temperature changes must not be caused by the Earth getting farther from and closer to the Sun. Otherwise, we’d have summer when the Earth is closest to the Sun. The seasons are caused by the angle of the sunlight hitting the Earth. In the winter, sunlight hits the Earth at a very low angle, an angle far from perpendicular or straight up and down. This means that a given “bundle” of sunlight is spread out over a large area and does not warm the surface as much as the same bundle in the summer.
Tuesday: Jupiter is about three fists above the southwest horizon at 7 p.m.
Wednesday: As a follow-up to the 1982 hit “Southern Cross”, Crosby, Stills, Nash, and Palmquist are working on this: “When you see the Northern Cross for the first time. You’ll understand now why swans fly this way”. The Northern Cross, also known as Cygnus the swan, appears to standing up on the northwest horizon at 8 p.m. The bottom of the cross about one fist and the bright star Deneb at the top of the cross is three fists above the northwest horizon.
Thursday: The holidays are family time. Now that the time you have spent with your human family is over, spend some time with your solar system family. This year begins the International Year of the Solar System. Nearly each month has a different theme. The theme for January is “A Family Affair”. Your solar system family has some great 3-D pictures posted at http://www.jpl.nasa.gov/multimedia/slideshows/index.cfm?id=22&page=1. They’re a lot better than the pictures of your aunt’s dog and that stupid doggy sweater he wears.
Friday: Saturn is nearly four fists above the south horizon and Venus is nearly two fists above the southeast horizon at 6:30 a.m.
The positional information in this column about stars and planets is typically accurate for the entire week.
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