Jupiter

It's about time that I talk about more than your monthly night sky report.  I decided this post should be all about Jupiter since it was recently at opposition in May, and is now a perfect target for binoculars and telescopes, or even the naked eye.

Jupiter was first viewed through a telescope by Galileo in 1610.  He saw the four largest moons, Io, Ganymede, Europa, and Callisto (AKA: The Galilean moons) orbiting Jupiter and used this as evidence to prove that the solar system was heliocentric and not geocentric as was the popular belief during this time.  I encourage you to purchase an inexpensive pair of binoculars to view the Galilean moons.  I own a pair of astronomy binoculars which are 25 X 100 and require a tripod to hold them steady.  A smaller pair such as 7 X 50 or even 7 X 35 can reveal the Galilean moons and are much easier to hold steady with nothing more than your hands.  I had a hard time giving up the view through my binoculars to others during my first time looking at Jupiter.  You can obviously use the binoculars for many other things such as bird watching, but I would recommend using them to look at other astronomy related targets such as the Moon and Venus.

For other details of Jupiter, such as the cloud bands, the Great Red Spot, or seeing the moons transit the surface, you will need a telescope.  I have been able to see all of this with my telescope and enjoy the views every time.  The views can be enhanced with color filters and different eyepieces which I am excited to try in the future.

Jupiter is composed mostly of gas but may contain a small core.  The atmospheric pressure of Jupiter is so great that nothing would be able to reach the center before being crushed.  The cloud bands give off different colors due to the elemental composition of each band.  These colors are typically tan-brown to orange-red in color.

The Great Red Spot of Jupiter is a giant storm that is large enough for 2-3 Earth's to fit inside.  The Great Red Spot has been visible since the 1830's.  The existence is still a mystery as well as its slowly shrinking size.  Many other storms have formed on Jupiter and have since died away, so perhaps the Great Red Spot is slowly disappearing as the storm weakens.

Jupiter has many natural satellites such as the Galilean moons and many smaller sized objects.  Each year, the number of known satellites increases as our instrumentation gets better.  Currently there are 69 known satellites orbiting Jupiter.  They range in size with Ganymede being the largest, which is larger than the planet Mercury and some smaller than the size of a city at approximately 3 miles.  A few of these satellites are actually captured asteroids from the asteroid belt.  Astronomers know this because they are orbiting Jupiter in the opposite direction of the other satellites.

Many objects appear to produce light from reflecting the light from the Sun, such as the Moon and Venus.  Certain objects have a higher degree of reflectivity due to their composition.  Venus is covered by a thick cloud layer which reflects nearly all of the light that it receives from the Sun.  This causes Venus to be the third brightest object in the sky with the Sun and the Moon being the only objects that are brighter.  Jupiter was a mystery for many years because it was giving off twice as much energy than it received from the Sun.  I use the word "energy" here because to see this, you need to look at Jupiter in the infrared instead of visible wavelengths.  It was once thought that perhaps Jupiter was completely radioactive.  By doing some calculations, which I did recently in an astrophysics class and will not bore you with, if the entire planet of Jupiter was radioactive, it would still not give off as much energy as it does.

So what is the cause of Jupiter's energy emission?  The current hypothesis is that Jupiter is actually shrinking!  The difference in size would hardly be noticeable to us.  It would have to shrink by only 500 kilometers (approximately 311 miles) every billion years for it to radiate the amount of energy that it does.  Our solar system is estimated to be approximately 4.7 billion years old.  This would mean that over the life of the solar system, Jupiter would have only had to shrink by about 2300 kilometers (1430 miles).  The average person drives ten times this amount in one year!

As mentioned in an earlier post, there is currently a space mission at Jupiter.  The spacecraft, Juno, was launched in 2011 and arrived at Jupiter in 2016.  Juno is studying the composition, gravity field, and magnetic field, among other things, of Jupiter.  You can learn more about this mission and see stunning photos of Jupiter by clicking here.