Monday, December 28, 2009

The Ellensburg sky for the week of 1/2/10

Saturday: If the Sun looks big today, your eyes are not playing tricks on you. The Earth is at perihelion at about 4 p.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. 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.

Sunday: Today’s weather forecast: showers. Meteor showers, that is. The Quadrantid meteor shower peaks this afternoon at making this morning and tonight into tomorrow morning the best times to see meteors. 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 Draco the dragon. This point is about three fists above the northeast horizon at 1 a.m. In good years, careful observers can spot about 100 meteors per hour. Unfortunately, this will not be a good year to view the Quadrantids because the waning gibbous moonlight will 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: You never see a giraffe on the ground in Ellensburg. But you can look for one every night in the sky. The constellation Camelopardalis the giraffe is circumpolar from Ellensburg’s latitude of 47 degrees north meaning it is always above the horizon. Don’t expect to be overwhelmed by the appearance of the stars in Camelopardalis. The brightest star in the constellation appears only about half as bright as the dimmest star in the Big Dipper. However, the actual luminosities of the three brightest stars in Camelopardalis are very high, each at least 3,000 times more luminous than the Sun. Alpha Camelopardalis, a mind boggling 600,000 times more luminous than the Sun, is seven fists above due north at 10 p.m.

Tuesday: Jupiter is one and a half fists above the southwest horizon at 6 p.m.

Wednesday: What you see with the naked eye isn’t all that can be seen. While astronomers can learn a lot from observing the sky in the visible wavelengths, many celestial objects radiate more light, and more information, in wavelengths such as radio, microwave, infrared, ultraviolet, x-ray, and gamma ray. Last month, NASA launched the Wide-field Infrared Survey Explorer (WISE) to study objects that radiate in the infrared range such as asteroids, cool dim stars, and luminous galaxies. For an interesting comparison of how different wavelengths show different aspects of a galaxy, go to If it wasn’t for infrared telescopes such as WISE, astronomers would not know about the significant amount of dust in galaxies.

Thursday: This morning’s final quarter Moon is right on the border of the constellations Corvus the crow and Virgo the goddess of the harvest. At 7 a.m., the bright star Spica is about a half a fist to the upper left of the Moon.

Friday: Mars is three fists above the east horizon at 10 p.m.

The positional information in this column about stars and planets is typically accurate for the entire week.

No comments: