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  • Writer's pictureLuke


Now that Venus is gone from our evening sky you may be noticing the other bright star that appears over the western horizon. This “star” is actually the planet Jupiter.

Jupiter is currently “in Scorpio”. You will see a bright star with a red/orange hue just a little south of Jupiter, This star is Antares. Antares is not to be confused with mars which is currently high in the south west sky much further from Jupiter (this is such a common mistake it is where Antares name came from).

Take note of the distance between Jupiter and Antares, if you want a technical measurement you may hold your arm outstretched close one eye and see how many fingers you can fit between Jupiter and Antares. If you do this over the next few months you will see Jupiter get closer and closer to Antares. The star Antares is the heart of the scorpion or Scorpio.

Scorpio you might be familiar with from the zodiac over the course of a year we can watch Jupiter move from the constellation Scorpio to the next constellation in the zodiac Sagittarius. Jupiter takes just a little less than 12 years to go around the Sun, there are 12 signs in the zodiac, Jupiter spends a year in each one!

Jupiter is the largest planet in our solar system at 11.6 times the size of earth in diameter (86,881 miles), making it 1,322 times the size of earth in volume. Being so massive has made Jupiter a solar system within our solar system.

Jupiter currently has 79 known moons. This number keeps increasing as recently as July of this year, 2018, we added 10 newly discovered moons to the total. We are not done adding to the number of known moons of Jupiter. Astronomers are discovering new moons of Jupiter so frequently the main trick has become making sure the newly observed moons are not the same as a moon we have previously counted.

The number of moons of Jupiter will also be changing further as new moons are likely about to be made and destroyed. Of the known objects going around Jupiter most are going the same direction but, some are going the opposite direction and just like if you go the opposite direction in a traffic circle collision is likely.

If you look at Jupiter with a decent pair of binoculars you will be able to see 4 of Jupiter's moons Io, Europa, Ganymede, and Callisto. These are called the Galilean Moons as they were first observed by Galileo in his small telescope. Telling them apart takes several observations over a long period of time as they are circling Jupiter and you can only see this movement edge on from Earth. To determine a moon’s true distance from Jupiter you must watch the moons to see when they stop getting further from Jupiter turn around and get closer.

All of the Galilean Moons are interesting places and studied extensively. Io is the most volcanic body in our solar system, Eropa is the smoothest body in our solar system it’s believed to have liquid water and therefore possibly life beneath it’s ice surface. Ganymede is bigger than the planet Mercury, and Callisto is the most cratered body in our solar system.

Jupiter’s moons served as one of the first standardized clocks. Jupiter’s moons movement is regular and predictable so the Royal Observatory in Greenwich calculated and published their future locations and local time (as would be shown on a sundial or pendulum clock) at Greenwich, forming the foundations for our time zones based around Greenwich Mean Time.

With a good pair of binoculars you can also see red stripes contrasted with white stripes this is Jupiter’s atmosphere. The change in coloration is caused by different compounds in the atmosphere that change color when exposed to the light of the Sun.

A really good set of binoculars or a decent telescope you can see the red spot which is an acid hurricane more than twice the size of earth that has been observed since at least 350 years ago. A day on Jupiter last about 10 hrs so over the course of a long winter night you can watch Jupiter do a full rotation by watching the great red spot do a lap around the planet.

Jupiter and the four Galilean moons as would be seen in a small telescope

If you want to see Jupiter in a really big telescope come along on one of my tours. Click here to see dates and book

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1 Comment

Aug 18, 2021

Lovely bllog you have

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