Observing Pluto – What Does it Take?

With New Horizons‘ flyby of Pluto and all the great images the spacecraft has been returning I’ve wondered: Is it possible to observe Pluto from one’s backyard?  Personally I’ve never bothered trying for Neptune and beyond as I knew my small 80mm aperture telescope would not be up to the task.  Nevertheless I looked up Pluto’s apparent magnitude and found that it varies between 13.6 and 16.3 due to its elliptic orbit around the Sun.  It’s last closest approach (perihelion) was September 1989, and unfortunately Pluto is currently distancing itself for its 248 year journey around the Sun therefore slowly dimming, sitting right now at apparent magnitude 14.

Pluto as viewed by New Horizons during flyby (14 July 2015) - NASA

Pluto as viewed by New Horizons during flyby (14 July 2015) – NASA

What size of telescope does it take to observe an apparent magnitude 14 object?  Based on the theoretical limits it should be possible to make visual observation with a 10in aperture telescope, but most would say you need a 12in if you plan to observe with an ocular.  Of course, equipped long exposure cameras you can have a smaller telescope, but a high focal length would be preferred to reduce to better pick it out from the background of stars.  And I’ve managed to pick up mag 14 stars in my photos with the Skywatcher 80ED with 60sec exposures.  Therefore Pluto should be accessible to backyard astronomy.  Note that at Pluto’s size and distance it shows up as a light point and not a sphere like the other planets.

Up to the challenge?  Middle of November will be a great opportunity to locate Pluto as it will swing within 1deg of Ksi 2 Sagittarius, a magnitude 3.5 star.  In the June edition, Sky & Telescope created a great star-chart to locate Pluto until December 2015.  Good Luck!

Click on image for Sky & Telescope Pluto 2015 Sky Chart

Click on image for Sky & Telescope Pluto 2015 Sky Chart

Reference: Sky & Telescope

Comet 67P/Churyumov–Gerasimenko : Where is it, and where will it be.

In my previous post I’ve mentions that coment 67P/Churyumov–Gerasimenko is currently between the orbits of Jupiter and Mars, on a trip towards the Sun.  While some comets take decades to become visible again this one has an orbital period of 6.44 years, therefore a frequent visitor.  That was one of the selection criteria for the target comet: short orbital period such that it did not take too much fuel or planetary gravity assist to intercept.

On August 13th it will be at it’s closest position to the sun (perihelion), therefore brightest and a good time to observe.  Afterwards it will be swinging back out towards Jupiter on its elongated orbit.  For people in the Northern Hemisphere, the best time to observe comet 67P will be after this August date.  Below is a chart showing that the comet will be visible in the early morning starting in June 2015, and will be visible at higher altitudes in the sky throughout the following months.

Comet 67P visibility for around 45 Latitude N.

Comet 67P visibility for around 45 Latitude N.

Below is a chart (click to enlarge) showing the position of 67P until November 15th.

Comet 67P/Churyumov–Gerasimenko sky chart for Nov 2014 to Nov 2015

Comet 67P/Churyumov–Gerasimenko sky chart for Nov 2014 to Nov 201

A good photographic opportunity will be August 8th when comet 67P will pass right under open cluster M35.

Comet 67P passing under Open Cluster M35

Comet 67P passing under Open Cluster M35

Graphics generated with C2A Planetarium Software