It’s a great weekend for planet watching

Post content by: Richard Cox

This week (May 10-16, 2010) and the coming weekend is an excellent time to go outside and find the ecliptic in the sky. You don’t need a telescope or even a pair of binoculars. A lot of backyard astronomy can be done by just taking a few minutes and going outside and looking.

The ecliptic is defined as the path of the Sun against the background stars, or the plane generated by Earth’s orbit. However, both of these statements are not very visually helpful. It’s difficult to see any background stars when the Sun is up, and it’s tough to find Earth’s orbit when we’re on it. However, the ecliptic is also described as the plane, or ‘flatness,’ of the solar system. All the major planets orbit the Sun relatively close to the ecliptic plane. There are also several bright stars that lie very close to the ecliptic. This week, we have three planets, the Moon and three bright stars that can help us see the ecliptic plane across the night sky.


When viewed at 10 pm, MDT on Friday, May 14, 2010:
Venus is low on the west-northwest horizon at a bright magnitude -4. Venus sets just after 11 pm.
Mars is high in the southwest at 45 degrees above the horizon. It has a reddish appearance and is a descent magnitude +1.
Regulus, the bright blue star in Leo, is just over 10 degrees east of Mars. Regulus is often referred to as an ecliptic star, because it is so close to the ecliptic.
Saturn is due south at 10 pm, 50 degrees above the horizon, at magnitude +1.
Spica, the bright blue star of Virgo, is also close to the ecliptic and is 34 degrees above the south-southeast horizon at the date/time specificed.


If that’s not enough, as Venus sets Antares, the red heart of Scorpius, rises in the southeast. Antares is a +1 magnitude star 5 degrees south of the ecliptic.
But wait, that’s not all. A young crescent Moon appears near Venus on the evenings of the 15th and 16th, also on the ecliptic plane.

I suggest that you do this more than one evening, just to make sure you know what you’re looking at. Once you recognize the ecliptic, watch the waxing Moon for several days, preferably at the same time each evening, and you’ll see it march eastward along the ecliptic.

(images generated with Starry Night Pro, v6.3.9)

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