Father Sky

Anyone who enjoys reading about the history of astronomy is quite familiar with the amazing story of the discovery of Neptune in 1846. How it was the first celestial object found not by chance or endless hours of random scanning, but by sophisticated mathematical calculation.

Let me briefly summarize: At that time Uranus was the furthest known planet from the Sun, (discovered in 1781 by William Herschel using the “endless hours” technique ). Over time, the tracking of Uranus allowed astronomers to calculate it’s orbit according to Newton’s laws of motion and gravity. But gradually Uranus kept deviating from it’s calculated orbit. Was there a problem with Newton’s laws or was there yet another planet out there gently tugging at Uranus which caused this orbital error? John Couch Adams of England and Urbain Le Verrier of France independently took up this challenge. Using the positions of Jupiter, Saturn and Uranus they calculated where this mysterious new planet should be.  Due to some mis-communications on the English side, Johann Galle under instructions from Le Verrier was the first to observe Neptune. I’ll stop this story there but I certainly invite you to go to your local library to get the whole story.

It is this second interesting story regarding Neptune which brings me to write. Two centuries earlier, in 1613, Neptune was actually in the field of view of Galileo while he was observing Jupiter! Due to cloudy conditions, he only got to observe Neptune a couple of nights before it moved out of his field of view. With those few observations he just assumed Neptune was a background star so Neptune remained unknown for another 233 years.

Last night I took my little 80mm refractor out to see just what does Neptune look like in a small scope and how likely was it for Galileo to have made the discovery instead of Le Verrier? I’m sure my small refractor is still better than anything Galileo had in his day but then he probably had much better skies than what we put up with.  So, not exactly an equal test but this was just for fun anyway. Armed with an on-line ephemeris calculation and a nice star chart for that region of the sky I started scanning for my target. I found the location without too much fuss and started matching up stars on my chart with points of light in the eyepiece. Boy, it was not obvious! Finally, I found an “extra” point of light and spent the next 5 or 10 minutes going back and forth from chart to scope to verify it wasn’t plotted. But let me tell you. That was the only indicator this was something other than a star. No color, no disk, just a point of light.

Galileo was an amazing person, but I doubt even he could have determined that point was Neptune.

It was a fun experiment.