Wednesday, December 26, 2018
The Ellensburg WA sky for the week of 12/29/18
Saturday: A new year, a new target for New Horizons. At 9:33 p.m., Pacific Standard Time on December 31, New Horizons, the probe that taught us so much about Pluto in 2015, will be make its closest approach to Ultima Thule. Because Ultima is so far from Earth, the signal with the first information won’t reach Earth for about ten hours. Based on images from the Hubble Space Telescope, astronomers know that Ultima will be reddish in color and be either oblong in shape or consist of two spheroids close together like a dumbbell. During the flyby, astronomers will gather information to learn more about the geology and surface composition of Ultima, as well as whether or not it has rings or moons. For more information, go to .http://pluto.jhuapl.edu/.
Sunday: Spica is one fist to the lower right of the Moon at 7 a.m. Throughout the week at 7 a.m., the Moon will be passing by three planets in the morning sky. On Tuesday, Venus will be to the lower left of the Moon. On Wednesday, Venus will be to the upper right of the Moon and Jupiter will be to the lower left. On Thursday, Jupiter will ba a half a fist to the right of the Moon. Finally, on Friday, Mercury will be squeezed between the Moon and the southeast horizon.
Monday: The bright star Regulus is two and a half fists held upright and at arm’s length above the east horizon at 11 p.m.
Tuesday: 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. The International Astronomical Union promoted Ceres to the status of “dwarf planet” in August of 2006.
Wednesday: 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 21 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 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. For more information, go to http://goo.gl/SJC5r.
Thursday: Late tonight and early morning’s weather forecast: showers. Meteor showers, that is. The Quadrantid meteor shower peaks late tonight and early tomorrow morning between midnight and dawn. 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 above the northeast horizon at 1 a.m. This year, the Moon will be below the horizon so you may be able to see up to 100 meteors per hour. 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. For more information about the Quadrantid meteor shower, go to http://earthsky.org/?p=155137.
If the Sun looks big today, your eyes are not playing tricks on you. The Earth is at perihelion at 12:19 a.m., Pacific Standard Time today. 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. For the Northern Hemisphere, that very low angle occurs in December, January and February.
Friday: Mars is four fists above due south at about 5 p.m.
The positional information in this column about stars and planets is typically accurate for the entire week. For up to date information about the night sky, go to https://nightsky.jpl.nasa.gov/planner.cfm.