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If you have been out at dusk lately You may be noticing the brightest star that appears over the southern horizon just after sunset. This “star” is actually the planet Jupiter!
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, you could fit over a thousand earth's inside Jupiter. Being so massive has made Jupiter a solar system within our solar system, as it's extreme gravitational pull captures lots of objects as moons of Jupiter.
Jupiter currently has 79 known moons. This number keeps increasing as recently as July of 2018, we added 10 newly discovered moons to the total. 26 of the moons are so new they are still awaiting official names. 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 of traffic in a traffic circle collision is likely.
If you look at Jupiter with even just a halfway 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. They are very easy to make out even in small telescopes/binoculars but, telling which one is which 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. (or you can just cheat and use this web tool)
All of the Galilean Moons are interesting places and studied extensively. Io (the closest) 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 (the furthest out) 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. This has been the only silver lining of stargazing in Colorado thru the smog/haze from the wild fires in the mountains is that the haze has been increasing the contrast on Jupiter making the stripes and spot easier to see (I've actually been able to make out a personal record number of stripes this year seeing 7). 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 is currently “in Capricorn ”. Capricorn doesn't look like much unless you have really dark sky, but you will see Sagittarius to the right, right next to it! If you have decently dark skies and some imagination you might see a constellation that resembles a teapot just to the right of Jupiter. A triangular lid atop a trapezoidal body with a trapezoidal handle on the east side and a triangular spout on the west side. Even better if you are in a particularly dark area you can see the milky way appearing as steam coming out of the spout. This “teapot” was originally seen as an archer, and named Sagittarius. The tip of the spout to the two stars that make the top of the handle are the arrow and the top of the lid and the two stars to the right of the base make the bow for the archer.
The archer's arrow is drawn pointing to the west towards a bright star with a red/orange hue. This star is Antares. Antares is not to be confused with mars which is currently rising in the eastern sky around 10pm ~ish (this is such a common mistake it is where Antares name came from, it's Arabic for 'rival of mars'). The star Antares is the heart of the scorpion or Scorpio. and Sagittarius is protecting others from Scorpio by keeping his bow drawn towards it's heart.
Capricorn, Sagittarius, and Scorpio you might be familiar with from the zodiac over the course of 12 years we can watch Jupiter move across every sign in the zodiac. If you read my post on Jupiter two years ago you have been able to watch Jupiter move from the constellation Scorpio to the next constellation in the zodiac Sagittarius and now to Capricorn! Jupiter takes just a little less than 12 years to go around the Sun, there are 12 signs in the zodiac, therefore Jupiter spends a year in each one! so next year we can be sure to find Jupiter in Aquarius!
Come get a closer look at Jupiter seeing it's stripes (this year better than ever with the haze), moons, red spot and more! On an astronomy tour! Book now for an out of this world experience!