Jupiter

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

Venus

Watching the sky just after sunset you may be noticing the brightest star that appears over the western horizon. This “star” is actually a planet (or wandering star) Venus.

Venus is the third brightest naturally occurring object in our sky (after the Sun and Moon) due to having a thick atmosphere with clouds that reflect sunlight really well. Venus is the closest planet to the Earth and about the same size as Earth both of which also attribute to its brightness.

The key to understanding Venus’s movement in our sky is to remember it’s an interior planet which means it travels around closer to the Sun in an orbit interior to ours. It takes Venus a little over 7 months to travel around the Sun where it takes Earth 12 months. This means every year Venus will pass us on the inside lane at least once. Right now Venus is catching up and will pass us on the inside lane on October 26th. This is called ‘inferior solar conjunction’ and means the Sun, Venus, and Earth will be in alignment. We won’t be able to see it pass us as it will be too close to the Sun to observe. Here in the Front Range, we will stop being able to see Venus in our evening sky in early October due to the mountains covering anything low on the western horizon.

We can’t watch Venus pass us, but right now we can watch it move in for the pass. If you watch the sunset every week or so until October you will see Venus getting closer and closer to the horizon. A few days after inferior solar conjunction (October 26th) we will start seeing Venus on the other side of the Sun in our sky just before sunrise. Watching the Sun rise starting in November you will see Venus climb higher and higher in the morning sky. Venus never travels further than 47 degrees from the Sun. Because of this we only notice Venus at sunset or sunrise when the Sun is blocked by the horizon letting Venus shine in the sky. One small exception to this is during a solar eclipse when the Sun is blocked by the Moon. Some may have noticed Venus next to the Sun during last year’s solar eclipse.

Looking at Venus with a decent pair of binoculars you will see that it currently appears as a crescent. This is because just like the Moon, Venus has phases. Because Venus is currently coming toward us, we can see a portion of Venus that is illuminated by the Sun and a portion that is in darkness (night) facing away from the Sun. The illuminated portion will continue to shrink until Venus is in inferior solar conjunction when we won’t see Venus just like we don’t see the Moon at New Moon. Then in November as we watch Venus rise before the Sun we will also, if we check in weekly with binoculars, see the illuminated crescent grow larger.

Phases of Venus - As we watch the crescent of Venus get smaller "wane" we notice Venus get larger as seen in this picture. This is because Venus is coming closer to us. Venus seen from earth is actually brighter as a crescent then when it is full because of this.

Introduction to the series:

We currently have the best of planets in our night sky for astronomy! For the next couple weeks, I want to take a detailed look at each one with you.

Let’s start by finding and identifying them. Watching the sky after sunset you may be noticing the brightest star that appears over the western horizon during twilight. This “star” is actually the planet Venus! The word planet actually means wandering star because the planets appear to move amongst the stars. Venus is quickly disappearing so much so it's hard to see right now because it is really close to the sun. With the mountains on our western horizon it makes it extra difficult.

Now, drawing an imaginary line south east in the sky from Venus you should run in to another bright ‘star’. This is not as bright as Venus but usually the second point of light that comes out during twilight. This is another planet, Jupiter. Jupiter is currently near a fairly faint star with a really fun name- Zubenelgenubi (I say it zoo-bin-L-gha-new-bee, but you may say anything fun you want). This star represents the southern end of the balance beam of Libra. Now as the reader of a paper you might be familiar with the constellation Libra from the horoscope section and that’s no coincidence. If we look back at Venus we see it too is near a bright star Spica. Spica is the brightest star in Virgo, another constellation you might find a horoscope for. Spica is currently appears closer to the sun than Venus so it will be extra hard to see.

Let's take this line we drew connecting Venus and Jupiter and continue it on. You should also see an obvious red dot of light appearing in the south east, this is Mars. Let’s arch this line a little and put Mars on the line too. Almost halfway between Mars and Jupiter (a little closer to Mars than Jupiter) on this line you might see another brighter light, this is Saturn. If you have dark skies and some imagination you might see a constellation that resembles a teapot below Saturn. This “teapot” was originally seen as an archer, and named Sagittarius. Next to Mars you’re going to need a lot of imagination (or beer) for this but you might make out a horned goat, Capricorn. If you’re following along with the horoscope section you may of noticed I missed Scorpio which currently has no planets but has a truly red star Antares (which means Mars’s rival) that is about halfway between Saturn and Jupiter on this line.

This line connecting all the planets is a very special line we call the ecliptic. The ecliptic simply is the plane of our solar system therefore this line is the only place you will find planets. You can complete the ecliptic, as it circles around the Earth, if you keep drawing the line below your feet and circle the line back to Venus. The Sun and Moon are also on this line! This line is so important, every constellation it passes through is in the zodiac. That’s what the zodiac is for, to denote the plane of the solar system in the sky (not just to fill up the paper). The constellations of the zodiac are therefore the only constellations that are ever visited by planets.

Let’s go back to Jupiter next to Zubenelgenubi. Zubenelgenubi is the part of the balance beam of Libra. So, we can say Jupiter is in Libra. All of the planets, the Sun, and the Moon can be said to be in a certain constellation of the zodiac.

For the next month we will look in detail at each one of these planets along the ecliptic moving west to east in the sky. Check back here next week to learn more about Venus.