Astro Bob: Impostor moon drops in on Jupiter – Duluth News Tribune

Jupiter has a big and numerous household with 95 identified moons. You are most likely already accustomed to the largest ones found by Galileo again in 1610 — Callisto, Ganymede, Europa and Io. The opposite 91 do not get close to the eye from observers as a result of they’re exceptionally faint. Even devoted amateurs see not more than 4 Jovian moons except they’ve entry to a bigger telescope (not less than 12.5 inches) and detailed map. Thus geared up one would possibly add one further moon to their life lists, the vanishingly faint


. That is why I perked up Friday night time (Aug. 18) when an observer on the

Chippewa Valley Astronomical Society’s

annual Starfest casually talked about that his telescope confirmed 5 moons.

Jupiter Aug. 20

Use this chart to identify the impostor moon Sigma Arietis on Sunday night time, Aug. 20. South is up on this and all the opposite maps to match what you will see by means of a typical reflecting telescope. Moon positions are proven for round midnight Central Time.

Contributed / Stellarium

I came to visit for a glance. Certain sufficient. Three moons gleamed to the east of Jupiter and two to the west. One instantly aroused my suspicion as a result of it wasn’t fairly in keeping with the others. A fast test revealed the interloper because the star Sigma within the constellation Aries, or just Sigma Arietis. Its brightness matched the opposite Galilean moons and the alignment with the others shut sufficient to trick a novice observer.

Jupiter moon Aug. 21-22

Positions of the moons and Sigma are proven for Monday and Tuesday nights, Aug. 21 and 22 round midnight CDT. Discover that as Jupiter strikes to the east (proper) the moon seems to slip farther to the west. Sigma will go closest to the planet (solely about 9 arc-seconds to its south) round 5 p.m. CDT on Aug. 21 when Jupiter is not seen in North America.

Contributed / Stellarium

The subsequent night time, Jupiter once more sported “5” moons however Sigma had shifted place barely — it was now nearer to the planet and much more convincing. A more in-depth look revealed that the impostor could be hanging across the large planet for practically every week. Meaning you will have an opportunity to see it, too. Over the following a number of nights the star will seem to maneuver westward, closing in on Jupiter after which departing. In fact, that is an phantasm. Sigma would not budge. Jupiter does all of the shifting!

Jupiter moon Aug 23-24

Positions are proven for round midnight Wednesday and Thursday nights, Aug. 23 and 24.

Contributed / Stellarium

As the large planet orbits the solar it slowly glides east throughout the night time sky. It so occurs that Sigma lies alongside the planet’s path and its brightness is a close to match to Io and Europa. A outstanding factor actually. Every night time that Jupiter advances to the east this short-term moon will seem to glide west throughout the Jovian system. As you comply with the scene, contemplate that you are looking at a star 470 light-years away that is 3 times the scale of the solar and practically 4 occasions as large.

Jupiter Aug 25 midnight.jpg

Positions are proven for round midnight CDT Friday night time, Aug. 25. Sigma is simply beginning to exit the image.

Contributed / Stellarium

Come Aug. 25-26 Jupiter will probably be far sufficient away from the star that we will kiss this poser goodbye. Then once more perhaps not. Annually, the sooner Earth laps Jupiter when the 2 planets line up on the identical aspect of the solar at opposition. That is after they’re closest. Previous to opposition Jupiter seems to decelerate within the sky, cease briefly after which again up and head west. Image your self driving on the freeway passing a slower automotive. As you flip to look again, the automotive seems to maneuver backward. The identical factor occurs once we go Jupiter.

Jupiter viewing time

Jupiter makes an look within the japanese sky with the Pleiades round native midnight. Later in August you will spot it nearer to 11:30 p.m.

Contributed / Stellarium with additions by Bob King

Jupiter will come to an obvious halt on Sept. 4. Then it’ll again up and go Sigma a second time from Sept. 11-20. Little bit of unhealthy information although. It is going to glide to the south of the star, so will probably be straightforward to tell apart from the 4 Galilean moons. They orbit fairly near Jupiter’s equatorial airplane, biking round large very similar to the planets across the solar. Galileo noticed the orbiting Jovian moons as robust proof for a sun-centered photo voltaic system, a radical concept on the time. These days it simply is sensible.

Bob King

“Astro” Bob King is a contract author and retired photographer for the Duluth Information Tribune. You’ll be able to attain him at


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