From our Other Members...

Searching for Pluto

The best time to look for Pluto is in July and August, during the week following the Last Quarter Moon. A clear dark sky with the Moon below the horizon until after midnight or 1 am is ideal. A 12-inch or better telescope is needed, with tracking, so you can switch to high power (e.g. > 150x) when you find the right star field. It’s quite a challenge to positively identify Pluto. The computer can point the scope to the right star field, but that is only the beginning of the search. Then you switch to the Pluto finder chart in the June issue of Sky and Telescope. It plots stars to magnitude 14.5, with Pluto’s track (magnitude 14.1) shown as a yellow line. Find a recognizable star field that will serve as a good reference point. The trick is to identify the pattern of stars around Pluto, and determine exactly which stars are nearest to it on the night you are observing. The finder chart is essential for this part.  Don't forget to turn the finder chart upside down to match the view in a newtonian or schmidt cassegrain without the star diagonal.

 In August 2014, Pluto had a declination of about -20.5 degrees (pretty far south), so it was important to look just when Pluto was highest above the horizon. Pluto’s maximum possible altitude at Reno is only about 30 degrees and this is reached before midnight in July and August. So we needed to get the scope set up, cooled, and aligned during the twilight. With the computer it was a snap to find the right star field. Then we boosted the magnification to 240x and started looking. Even with plenty of dark adaptation and averted vision, it took three tries (three nights) to find Pluto.

Pluto was at opposition on July 4th in 2014. If you begin looking in July, you would have more time after the end of twilight to do the search, as familiarity with the star field is really critical. While spending the time to understand the star field and know exactly where to look,you can debate whether Pluto is actually a planet or merely a dwarf planet.

This search was a very satisfying experience because everyone knows about Pluto but few people have actually seen it. Once you do there is a sense of awe. I think it helps sharpen a person’s observing skills too. I plan to try again in 2015 and hope others are willing to give it a try as well. Now that I have seen Pluto with my own eyes, I’m anticipating the arrival of the New Horizons space craft at Pluto in 2015 to show me what I cannot see with an earth-based telescope.

Category: Other Members