Jupiter As Close As It Gets

Our planet Earth orbits the Sun once every year whereas it takes Jupiter about twelve years to complete one orbit.  This means that once every thirteen months Earth catches up to Jupiter and passes it in this planetary race around the Sun.   When Earth “passes” Jupiter, we say that Jupiter is at “opposition”.  This year’s opposition is happening today.

At opposition, Earth lies almost directly between the Sun and Jupiter.  As a result, Jupiter is as close to Earth as it ever gets. Today, it is 3.97 astronomical units (au) away.  One “astronomical unit” refers to the distance from Earth to the Sun.  Hence, to say that Jupiter is 3.97 au away is to say that it is just a little bit less than 4 times further from us than we are from the Sun.

Earth orbits the Sun at a distance of 1 au (by definition).  Jupiter orbits the Sun at a distance of 5 au.  As shown below, depending on where Earth and Jupiter are in their orbits around the Sun, the distance from Earth to Jupiter varies between 4 au and 6 au.  It is 4 au at opposition and 6 au  when it is behind the Sun.

Orbits of the Inner Planets Around the Sun
Orbits of the Inner Planets Around the Sun

Now is the best time to view Jupiter in a small telescope.   Shown at the top of this page is a picture I took of Jupiter just a few days ago.  In this picture, Jupiter’s apparent size is as big as it ever gets for the particular telescope and camera I used.

In terms of “angular size”, Jupiter is currently 49.6 arcseconds in diameter.  An “arcsecond” is a measure of angular size.   We are all familiar with the concept of “degree”—there are 360 degrees in a full circle.  An “arcminute” is a smaller measure of angular size.  There are 60 arcminutes in one degree.  An arcsecond is even smaller.  There are 60 arcseconds in one arcminute.  Hence, 49.6 arcseconds is the same as 0.83 arcminutes.  To put this angular size into more familiar terms, note that the Moon is about 31 arcminutes in angular diameter.  Hence, the Moon currently appears about 37 times bigger than Jupiter.

To appreciate the changing apparent size of Jupiter, it is interesting to compare pictures taken with the same equipment at different times.  Last August, I took a picture of Jupiter with the same equipment that I used a few days ago.  Shown below are the two pictures side-by-side.  Jupiter today is clearly bigger than it was back in August.  When I took the August picture, Jupiter was 4.50 astronomical units away.  Hence, its apparent size was about 15 percent smaller then than now as the picture shows.

Jupiter in August and October
Jupiter at opposition and 2 months earlier

Even though Jupiter is at closest approach right now, it will be an excellent evening object to view over the next several months.   Currently, it rises in the east exactly when the Sun sets in the west.  About an hour after sunset it is the blazingly bright object low in the east.  Most people will think it is just another airplane off in the distance but those of us who know better can tell our friends that, no, this bright object is the majestic planet Jupiter.

Over the next few months, we will slowly draw further and further ahead of Jupiter in our orbit around the Sun and Jupiter will start to look smaller in the telescope.  But, this regression will take place gradually and therefore Jupiter will continue to be spectacular for at least the next few months.

Jupiter and three of its Moons
Jupiter and moons Europa, Ganymede, and Io

More detailed information on the equipment used can be found at http://www.princeton.edu/~rvdb/images/NJP/jupiter.html.

Robert J. Vanderbei is chair of the Operations Research and Financial Engineering department at Princeton University and co-author of the National Geographic book Sizing Up the Universe. Vanderbei has been an astrophotographer since 1999, and he regularly posts new images on his astro gallery website.
  • Paragjyoti Chetia

    I would like to know the exact time of Jupiter getting close to the earth today.

  • Kunal Deep Baishya

    Really I found it very interesting to see a planet so bright in my lifetime, I never expected to see this. (KUNAL)

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  • francois

    Thre was a great shot of Jupiter just before the beginning of the bottom of the third inning in game five of the WS from Arlington. You could see the bands and three of it’s moons. But not a word form the booth analysts about this great shot. I’d sure like to have a lens like the one on those TV cameras.

    • Interesting. I didn’t watch game five so I didn’t see it. Sports photographers tend to have very nice equipment.

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  • person on earth

    How cool is that? Jupiter is my favorite planet.

  • BobT

    Lovely to look at but don’t want to get near. H’mm. Like some women I’ve known.

  • Lucy Pond, Astrologer

    This is so COOL!

  • Osbourne Mkhize

    i will like to know what’s happening around our milk way , i real want to know cause i deep belive that sumthing is going to heppand in our plant earth . but we need to stay posative all the time so im based i South Africa sum times i see things from out of space only when im sleeping . so i realy want to get infom about aour milk way &the galax

  • Gerard B. Noprada

    How was that strange!
    As every month it seens it gets big or small!
    How is that???????????

  • makey helo

    hello im makey and i would like to know more about jupiter 🙂

  • jaspreet

    i want basic information about the space

  • Shinta Nur Amalina

    Do you know what is the angular separation from Jupiter to Callisto (its outer Galilean moon)? Thank you

    • At its maximum, it’s a little less than 10 arcminutes. More precisely… 9m40s.

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