Monday, June 26, 2017

The Ellensburg WA sky for the week of 7/1/17

Saturday: Jupiter, the Moon, and Spica make a small triangle in the southwest sky at 10 p.m. Jupiter is the bright point of light one fist to the lower right of the Moon. Spica is dimmer than Jupiter and closer to the Moon in the sky at about a half a fist below the Moon.

Sunday: When it is sitting low in the western sky, many people mistake the star Capella for a planet. It is bright. It has a slight yellow color. But, Capella is compelling on its own, even though it is “just” a star. It is the fourth brightest star we can see in Ellensburg. It is the most northerly bright star. It is a binary star consisting of two yellow giant stars that orbit each other every 100 days. At 10 p.m., Capella is a half a fist held upright and at arm’s length above the north-northwest horizon. If you miss it tonight, don’t worry. Capella is the brightest circumpolar star meaning it is the brightest star that never goes below the horizon from our point of view in Ellensburg.

Monday: Hot enough for you? Don’t blame the Earth-Sun distance. Surprisingly, the overall temperature of the Earth is slightly higher in July, when the Earth is farthest from the Sun, than in January, when it is closest. That’s because in July, the Northern Hemisphere is tilted towards the Sun. (This is the real cause of the seasons.) The Northern Hemisphere has more land than the Southern Hemisphere. Thus, in July, the large amount of Northern Hemisphere land heats up the entire Earth about two degrees Celsius warmer than in January. In January, the watery Southern Hemisphere is tilted toward the Sun. But, water does not heat up as fast as land so the Earth is a few degrees cooler. The distance between the Earth and Sun is its greatest today, 152.1 million kilometers. This is called aphelion from the Greek prefix “apo” meaning “apart” and Helios, the Greek god of the Sun.

Tuesday: Tonight, while you are taking a break from looking at an explosion of fireworks, the NASA Kepler spacecraft is taking a break after finding an “explosion” of exoplanets. Last month, astronomers using the Kepler space telescope released a catalog of 219 new planet candidates. Ten of those are near-Earth size and orbiting in the habitable zone of their host star. And there are probably more to come. The Kepler spacecraft is monitoring the brightness of over 156,000 stars in the constellations Cygnus the swan and Lyra the lyre. This region is midway between the bright stars Deneb and Vega. It is about the size of your hand held at arm’s length and is about six fists above the east horizon at 11 p.m. For more information about this find, go to

Wednesday: Venus is one and a half fists above the east horizon at 4:30 a.m.

Thursday: Saturn is less than a half a fist to the lower right of the Moon at 10 p.m.

Friday: Mizar is a well-known binary star in the constellation Ursa Major. You can find it at the bend in the Big Dipper handle, nearly straight overhead at 10 p.m. tonight. Its name is Arabic for waistband. Mizar has an optical double called Alcor, which is less than a pinky width away and can easily be seen with the naked eye. Optical doubles are stars that are close together in the sky but do not orbit a common center of mass as true binary stars. Not wanting to deceive sky gazers who call Mizar a binary star, two stars that DO orbit a common center of mass, Mizar actually is a binary. It was the first binary star system discovered by telescope. Mizar A and Mizar B are about 400 astronomical units apart from each other and about 80 light years from Earth. 400 astronomical units is about 10 times the distance between the Sun and Pluto.

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

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