The Ellensburg, WA sky for the week of February 18, 2023

Saturday: On February 18, 1930, Clyde Tombaugh discovered Pluto, at that time classified as the ninth planet. However, as astronomers started discovering a lot of similar objects in that part of the Solar System, they realized that they had a classification crisis on their hands. Should everything in this region of the Solar System be named a planet? Eventually the International Astronomical Union (IAU) reclassified Pluto and all future Pluto-like objects as dwarf planets. This week you can celebrate the discovery with the people at Lowell Observatory, the “home” of Pluto’s discovery. Go to https://iheartpluto.org/ for more information about online events this weekend.

Sunday: Mercury is just barely above the southeastern horizon at 6:35 a.m. This is probably the last day you have a chance to see it in the morning sky for a few months.

Monday: This President’s Day, let’s remember Abraham Lincoln: 16th president, country lawyer, man on the penny, wrestler, and astronomer. Astronomer? Well, maybe not an astronomer, but someone who used observational evidence from the sky to solve a problem. In 1858, Lincoln defended Duff Armstrong, a family friend who was accused of murder. The prosecution thought they had a strong case because their primary witnesses claimed to have observed the killing by the light of the nearly full moon. Let’s listen in on the trial courtesy of the 1939 film, Young Mr. Lincoln.

Lincoln: How’d you see so well?

Witness: I told you it was Moon bright, Mr. Lincoln.

Lincoln: Moon bright.

Witness: Yes.

(Dramatic pause as Lincoln reaches for something)

Lincoln: Look at this. Go on, look at it. It’s the Farmer’s Almanack (sic). You see what it says about the Moon. That the Moon… set at 10: 21, 40 minutes before the killing took place. So you see it couldn’t have been Moon bright, could it?

Lincoln used the known information about Moon rising and setting times for August 29, 1858 as evidence in a trial. This is one of the earliest uses of forensic astronomy. For more information about Lincoln’s “almanac trial”, go to http://goo.gl/r83q4X.

Tuesday: Venus and Jupiter line up near the 1.5 day old waxing crescent moon throughout the day. Their proximity to the moon makes them good targets for daytime naked eye viewing. Wait until after 5:00 when the Sun is low in the sky and you can situate yourself so the Sun is behind something. First center the moon in the field of view of your binoculars. Then move your binoculars upward until you see a bright point of light. This is Venus. Next pull the binoculars away and look at that spot with the naked eye. See where it is with respect to the moon. Look away and look back again. Did you see Venus without binoculars? Now use your binoculars to move from the moon to Venus. Then move your binoculars to the upper left until you see another point of light, about one sixth as bright as Venus. Next pull the binoculars away and look at that spot with the naked eye. See where it is with respect to the moon. Look away and look back again. Did you see Jupiter without binoculars? This planet is more challenging because it is dimmer and farther from the moon in the sky.

Wednesday: Mars is nearly seven fists above due south at 7:00 p.m.

Thursday: It’s getting dark. The last remnant of twilight has disappeared. Suddenly, you notice a large softly radiant pyramid of light in the western sky. The base of this ghostly triangle is along the west horizon and the peak stretches two or three fists above the horizon. It is not really a ghost. It is an effect called the zodiacal light. This light comes from sunlight reflecting off dust grains in our solar system. The effect is the most visible when the band of constellations called the zodiac makes a steep angle with the horizon. You need a clear dark sky with no haze or light pollution to see the zodiacal light. At its brightest, the zodiacal light rivals the light of the central Milky Way. Look for the ghostly patch after twilight for the next few weeks.

Friday: Two bright stars, Vega and Deneb, are hugging the northern horizon together at 11:00 p.m. Vega, the brighter of the two, is about a half a fist above the northeastern horizon. Supergiant Deneb to two and a half fists to the left of Vega, closer to due north.

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.