Focus on Pluto: The Most Challenging Planet

How many people have seen the most distant and faintest planet?  Only those that have can claim to have seen them all.  Are you up to the challenge?  Oh, and yes, the Skyhound still considers Pluto to be a planet.  Even if you consider it to be a Trans Neptunian Object it is still the brightest of its class and the only one visible in amateur instruments, certainly making it worth observation.

On June 13 Pluto reached at opposition, 31 AU  from the sun and 32 AU from the earth.  One AU is the distance between the Earth and Sun.  Although opposition was in June, August provides and excellent opportunity to observe Pluto in the early evening.  And if you are looking for a real challenge, its tiny moon, Charon, can be as far away from the planet as 0.9".

What You Will Need
There are two essentials for successfully observing tiny Pluto: dark skies and a good finder chart.  We've provided the charts.  It is up to you to find the dark skies.  If you live in or near a bright city you will need to make a trek away from the lights.  But you wouldn't expect to hunt big game in your back yard, would you?

Under dark skies Pluto appears as a very faint star in a 6" scope.  Seasoned observers have reported seeing Pluto in even smaller instruments.

What You Will See
A faint, magnitude 13.8 star.  It is possible for an experienced observer to detect Charon in a large telescope under excellent conditions when the tiny moon is farthest from the planet.  But only a handful of observers have done it.

How Can You Be Sure You Saw It?
There is only one way to be certain you saw Pluto.  Go back another night and see if the faint star you think is Pluto has moved.  If it has, you have found it!

What Are You Seeing?
No spacecraft has visited far-away Pluto so we can't say for certain what it looks like up close.  However, it is highly likely that Pluto looks very similar to one of the smaller moons of the outer planets; perhaps like Neptune's Triton.  Pluto is a mere 2200 km in diameter (about 60% that of the moon) and its satellite, Charon, is about half that size.  The discovery of Charon in 1978 was important because its orbit tells us the mass of Pluto directly.  This and the  diameter of Pluto tells us its density, which in turn gives us a clue as to what Pluto is made up of.  The density of Pluto is very similar to Triton, which is made of a mixture of rocky materials and water ice.

Looking back at the sun from Pluto it would appear as nothing more than a bright star.  One thing about Pluto is quite clear: it is very cold!  The earth would be nearly invisible as a faint speck of light lost in the sun's glare.

Finder Charts for Pluto in August. 

Charon Information Resources used to make this page Deep Sky Observing Guides

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