Jupiter, The Giant Of Our Solar System
Jupiter is without a doubt one of the favorite targets for amateur
astronomers. It is big -- really big. The table below presents some of the
physical aspects of Giant Jupiter. Similar data for all of our solar system's
planets is available at
|Rel Dia (to Earth)
|Rel Mass (to Earth)
|Rel Mass (to All Planets)
|Rel Gravity (to Earth)
|Min Dist to Earth (mi*e6)
|Max Dist to Earth (mi*e6)
|Rel Dist from Sun
|Max Angular Size (arc-sec)
|Min Angular Size (arc-sec)
|Number of Moons
The table shows some of Jupiter's parameters as relationships to Earth
rather than absolute unit values. I think it helps one get a sense of Jupiter's
real characteristics, in that we have a sense of Earth's characteristics.
For example, to answer the question: "What's the diameter of Jupiter?", the
table shows Jupiter's diameter as 11.21 times Earth's diameter, rather than 89,000
miles. 89,000 miles seems a useless number without some kind of reference, but
11.21 times Earth's diameter immediately conveys information.
So here are some popular questions, and the answers, mostly in relative to
What is Jupiter's diameter? It's about 143,000 km, or nearly 89,000 miles.
But compared to Earth, it's about 11.21 times the diameter of Earth. Big, in
other words. That's it's apparent size as measured from Earth. It turns out,
we're actually looking at the diameter of Jupiter's thick atmosphere. Is there
a rocky planet in there somewhere? Probably not, at least nothing like the
rocky planet we call Earth. Some models suggest that Jupiter's atmosphere just
becomes thicker and denser as one goes toward the center of the planet, turning
to a liquid at some pressure, then perhaps to a slush, the finally a solid
core. Hard to say what it's really like at the bottom of Jupiter's atmosphere.
How far is Jupiter from the Sun? It's around 500 million miles, or 778
million kilometers, but perhaps easier to visualize is it's about 5.2 times
further from the sun than is Earth. So it gets about 1/25 the amount of
sunlight per square meter. Then again, since it's 11.21 times the diameter of
Earth, it has about 125 times the surface area of Earth. So the entire planet
gets about 5 times the solar energy of Earth, scattered over it's entire
All amateur astronomers know that the planet Saturn has rings around it,
making it one of the most beautiful objects in our solar system. But -- does
Jupiter have rings? Or is Saturn unique in that respect? It turns out that
Jupiter does have rings, probably from some of it's many moons colliding at
some time in the past. But don't expect to see Jupiter's rings with an amateur
telescope, they are far too small and tenuous.
Who discovered Jupiter? That's a question that doesn't
make direct sense, in that Jupiter is a naked eye object. In fact, other
than the Sun and Moon, one of the brightest objects in the sky. So even
cavemen saw Jupiter. The ancients after cavemen noticed that like the other
planets, something was strange about Jupiter. It's position, like the other
planets, changed with respect to the star background. Of course, the
ancients didn't know what Jupiter and the other planets were, just that they
moved with respect to the stars.
Copernicus was one of the first to likely grasp what a planet was, in that
he figured out that planets appear to move with respect to stars because,
like Earth, they orbit the Sun. Not a popular idea in his time, but it turned
out to be true none-the-less.
Galileo was the first to point a telescope at Jupiter. His instrument was
quite poor by today's standards, and didn't magnify enough or provide clear
enough details to show features of Jupiter that today's amateur astronomers
are familiar with. But with his early instrument, crude as it was, he saw
the four biggest moons of Jupiter. They are known as the Galilean moons in his
honor. Galileo figured out that the moons he observed were orbiting Jupiter,
as our Moon orbits Earth. You can see the Galilean moons yourself with just
a pair of binoculars.
Current Earth, Jupiter, and Saturn Relationship
How far is Jupiter from Earth? Even though the orbits of both Earth and
Jupiter are near circular, since they both orbit the Sun their distances
vary. When on opposite sides of the sun (call conjunction because from Earth
Jupiter appears to be near the Sun), the distance from Earth to Jupiter is
some 602 million miles. But when Earth and Jupiter are closer to one
another, when on the same side of the Sun (called opposition because Jupiter
appears to be opposite the Sun), they can get as near as 366 million
miles. The image above shows the current orbital relationship between
Earth and Jupiter.
Those distances answer the next question, what's the angular size of Jupiter
when viewed from Earth? When Jupiter is furthest away, it appears to be only
about 30 arc-seconds in size, only a bit bigger that Mars when it's at its
best. But when Earth and Jupiter are at their closest, Jupiter appears to be
about 50 arc-seconds in size, twice the size of the best Mars appearances.
That's about the angular size of the big Moon crater Copernicus.
Look through the table to see other interesting facts, like how many moons
does Jupiter have? A lot, over 60 at present count. All but the the Galilean
moons (Callisto, Ganymede, Io, and Europa) are invisible to amateur sized
telescopes, however. But the Galilean moons are certainly visible, and provide
much of the delight in observing Jupiter. They often eclipse the planet
(called a transit), and their shadows are easily visible as they move
across the clouds of the planet. I've watched moon transits with my
DIY 60mm refractor,
so the experience can certainly be enjoyed with even a small telescope.
One interesting fact I think is the gravity one would experience at the
visible extremity of Jupiter, as if one could stand on a platform suspended
at the top of Jupiter's clouds. As the table shows, Jupiter is much more
massive than is Earth, nearly 318 times as massive. So you might think that
standing on a platform at the top of Jupiter's clouds would crush you. But,
Jupiter's diameter is also big, putting any such astronaut much further
from the center of Jupiter than we on Earth are from Earth's center. So when
all is taken into account, one would only weigh about 2.5 times what they
weigh on Earth. Certainly noticeable, but not deadly. Still, at it's mass,
Jupiter has alone over 70% of the sum total mass of all the planets in our
Tips For Observing Jupiter
The Public Domain Jupiter Image below was Supplied by NASA/NSSDC
This Site Not Endorsed by NASA
The Jupiter image above is typical of what an amateur astronomer might
see on a good evening with a 10 inch or so telescope. Actually, the colors here
are more vivid than what might actually seen through a telescope. But the
details and Jovian features are about what a large telescope can observe.
The Jupiter View Through A Smaller Telescope
At left is an impression of the planet Jupiter that a smaller telescope
might give. First you'll notice that the image appears in mostly shades of
gray, and the finer details are lost. The image also has much less contrast.
Still an enticing image because you would be observing it live, but not like
you see in text books and magazines.
The image shows fairly well that even with a small telescope, some amazing
aspects can be seen. To get a good idea of what more aperture brings, check out the Simulated Views page.
Just keep in mind that even with a small telescope, such as the commonly
used 60mm refractor,
you can still make out the major cloud bands of Jupiter and occasionally some
additional details. You can also see the 4 Galilean moons of Jupiter. In fact,
the big moons of Jupiter, as mentioned earlier, are even visible as pin points of light through
nothing more than a pair of binoculars. Refractors in general tend to give superior planet views, partly because of their steadier images, and partly because of their superior contrast. I use a long focus 60mm telescope to good purpose, but something like the Orion Observer 70mm Equatorial Refractor Telescope would show more than my 60mm.
You can get more out of Jupiter observing sessions if you plan a bit before
going out to view. By that I mean it's nice to know what you are likely to see
at different times of the evening. You may want to find out what nights of the
week something interesting is happening that would be fun to view. There are a
number of ways to do that planning. One of the best ways to plan a Jupiter
observing evening is with a computer planetarium program, such as xephem, kstars, or stellarium. If you really
want to get into Jupiter observing, maybe a book specifically about Jupiter, like Jupiter: and How to Observe It (Astronomers' Observing Guides) would help you out. Jupiter offers more
variety to the observer than any of the other planets, with its Great Red Spot, moon transits, and other transient features.
You can also use this website to see what tonight's Jupiter
view will be.
The depiction above is the Jupiter View from the planetarium
program Xephem. It
shows the appearance of Jupiter and it's moon for tonight at about
8:00 PM Denver time. If you check this image each day, you'll have some
idea of when something interesting is about to happen. More of tonight's
sky presentations are available at Tonight's Sky.
The moons in this image are labeled with Roman numerals, with I = Io, II = Europa, III = Ganymede, and IV = Callisto.
To see whether the Great Red Spot on Jupiter is visible at any given
time, you can check out the Sky
and Telescope Jupiter Applet.
The Xephem diagram above will show you when the Great Red Spot is
visible, and when Jupiter's moons are in interesting configurations, or when one
or more of the moons are casting shadows as they move across the planet.
Some Jupiter Nomenclature
Observers of Jupiter use a set of abbreviations to indicate the features of
Jupiter. Being familiar with them will help you understand more of what you
read about the planet.
Above is a drawing with the zones and belts labeled with their common
nomenclature. This is a proper aligned image. Many telescope views show an
inverted or horizontally flipped image. The light band across the equator is
the Equatorial Zone (EZ). The rest of the surface is broken into zones
(light colored) and belts (dark colored). This drawing doesn't have all the
labels. It only labels what's visible through most small telescopes.
The features drooping from the NEB are called festoons. I've
managed to see festoons with a long focus six Newtonian, but not with my
smaller telescopes. I've seen a hint of them with some photographs shown on
my ETX 90 Astrophotos page.
The Great Red Spot (GRS) appears as a disruption in the SEB. The GRS varies
in color and contrast over the years. In the 2009 season I was unable to
glimpse it with a long focus 60mm refractor, though I know others have seen the
Red Spot with similar instruments in previous years. I have seen the Great Red
Spot in previous years with a 6 inch f/5 Newtonian.
In addition to these features, you may be able to see dark bars in
What Do You Need To View Jupiter?
Jupiter can be enjoyed with a variety of equipment. You can start
with just a pair of binoculars. With these, Jupiter will appear as a
very bright but unresolved object with up to 4 pin points of light
nearby. These points of light are the Galilean moons: Io, Europa, Ganymede,
and Callisto. If you look and count less than 4, the others are either
behind Jupiter and blocked from view, or in front of Jupiter and lost in
Moving up to just a 60mm, like the Orion Observer 60mm Altazimuth Refractor Telescope (Teal)
will show the darkening of Jupiter's
polar regions, and at least 2 dark bands, the NEB and SEB. At powers above 100x
you may well see additional bands, such as the NTB. You might see the Great
Red Spot if it's on the visible side of Jupiter, but don't be surprised if even
a 3 inch telescope can't show it sometimes. A telescope like this one may
be a little wobbly at high power because of the type of mount.
You can see shadow transits on Jupiter with a 60mm telescope, though you may
have to stare awhile until you see your first one. The shadows through a 60mm
are very tiny dots. Through larger telescopes the shadows are still just dots,
but they stand out better.
To get the best views of Jupiter, you might consider a long focus
refractor of 70mm or larger,like the Orion AstroView 90mm Equatorial Refractor Telescope
. Significant detail can be seen with a good 3 to 4 inch
refractor. Refractors do well on Jupiter because the contrast between
the zones and belts is not great, and refractors deliver the best contrast
for any given aperture.
telescopes, such as the Questar, Celestron, and Meade ETX series, do very well
on Jupiter. The Celestron
NexStar 90SLT Mak Computerized Telescope is a popular model that works well, complete with
computer-driven clock drive. The secondary mirrors of the Maksutovs cause them
to have a bit less contrast than quality refractors of equal diameter, but
Maksutovs are known for their crisp, chroma free images.
Also consider the 5 inch and larger Schmidt Cassegrain Telescopes (SCT),
like the Celestron
NexStar 6 SE Telescope. Like the Maksutov telescopes, the SCTs are very
compact and portable, and operate with f ratios in the f/10 range. The SCT also
makes a good general purpose telescope for a wide variety of target types.
Next best are probably Dobsonian telescopes of moderate to long focal
ratios, like the Orion
SkyQuest XT6 Dobsonian Telescope. Long focus Dobsonian telescopes in focal ratios of
f/8 or longer make excellent planetary telescopes. And don't assume you need a
six inch or larger, as the less expensive 4.5 inch models, like the Orion
SkyQuest XT4.5 Dobsonian Telescope work very well also, at a cheaper price. I have a 6
inch f/10 Newtonian that delivers very good planetary images. The longer focal
length Newtonian telescopes have flatter fields of view (no coma), less sensitivity to
alignment, and smaller secondary mirrors that lead to better contrast. An 8
inch DOB of moderate focal length makes a great all around telescope as well as
a good planetary performer.
Even a shorter focus telescope, like the Celestron
Omni XLT 150mm Telescope Newtonian Reflector can deliver quality images. My old Discovery
Newtonian (no longer available) is almost identical to the Omni XLT, and with
it I've seen Ganymede as it traversed the surface of Jupiter, the Great Red
Spot, and numerous moon shadow transits with my 6 inch f/5 Newtonian. It must
be precisely aligned to perform well, but it can deliver an enjoyable show.
There are things you can do to improve your Jupiter viewing. Let your
telescope cool down to ambient temperature before expecting it to deliver steady
images. The time this takes is longer for bigger telescopes, and generally
longer for reflector type telescopes. Don't observe over the top of nearby
buildings. The heat rising from the buildings will cause significant image
instability. If possible, observe when the planet is highest in the sky, rather
than low to the horizon.
Try using a color filter on your eyepiece. Yellow is a common filter
used to enhance the contrast of the Jupiter features. I generally use an
apodizing screen on my 6 inch f/5. That apodizing screen helps reduce
some of the light scattered by the secondary. That has the effect of slightly
If you need to get a telescope or observing accessory, try this custom
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The fun Jovian features are the Great Red Spot, festoons (if you can see
them), bars in the NEB, and possibly some white spots in the latitude of the
GRS. Certainly the positions of the moons are fun to track. The shadows of the
moons can be seen when they move across the surface of Jupiter. The shadows may
accompany their respective moon closely if Jupiter is near opposition, or
greatly lead or lag the actual moon crossing, depending upon Jupiter's position
with respect to the Sun.
On occasion, you can actually see a moon moving across the planet rather
than its shadow. Seeing a moon image as it moves across the planet is quite
difficult. The moons are bright, and so is much of the surface of Jupiter.
I have been able to see Ganymede move across Jupiter. On the occasion I
saw it, Ganymede was moving across the polar area where Jupiter is darker,
which made the moon just visible. I was observing on that occasion with
a 6 inch f/5 Newtonian.
If you do a little planning and following some of these suggestions, I'm
sure that you'll find Jupiter to be one of your most exciting observing
Try Some Jupiter Photography
If you have the patience and the time, you might try taking some
photographs of Jupiter. To do that, you'll need a camera, and the simplest
setup I've used successfully is a converted webcam and a laptop computer. For
a short cut, you can inexpensively obtain the Celestron StarShoot
camera. With one of these
cameras you can take film strips (avi files) of Jupiter, getting a
few dozen images at a time. The you can use a stacking program like
Registax to combine the
images into a very nice rendition.
To help you get some ideas, you can review my Quickcam Astro Camera howto page, and my
Celestron NexImage Review page. The Quickcam page shows how to make your own astro camera from a
web cam, and the other shows how the Celestron NexImage camera works as well
as how to process and stack images.
Below you see some example of web cam and NexImage photos taken through
some of my telescopes.
Jupiter. 60mm f/17 telescope with Celestron NexImage camera. In this inverted image, the NEB (brown belt) is easily seen. You can also just see a shaded region where the SEB usually is visible, but not in this 2010 image when the SEB all but disappeared. Also visible is the NTB and the darkened polar caps.
Jupiter Image, Nov 5, 2010, ETX90 With Celestron NexImage Webcam, 2x Barlow, stack of 82 frames. Note GRS and missing SEB.
||Jupiter Image, Oct 16, 2000, Modified QuickCam Express Webcam, 6" f/5 Newtonian, 4x Barlow.