Neptune - 162 years later

Session name: 20080923.2100



On 23 September 2008, 162 years passed since Neptune was first discovered in the telescope by Johnann Galle relying on predictions of mathematician Urbain Le Verrier.

At an average distance of 4.5 billion km, Neptune takes 164.79 years to complete one orbit. For the Neptunian inhabitant, on July 12, 2011 Neptune will have completed one lap around the Sun since it was first observed by Galle.

Today, Neptune is the most distant of the 8 planets, by revision of astronomical definitions. From 1979 to 1999, Neptune was the most distant of 9 planets, prior to the revision of astronomical definitions and because Pluto's highly eccentric orbit brought the ninth planet inside of Neptune's nearly circular orbit. This will occur again between 2216 and 2236.

From the city, the early Autumn Sky rising in the east may appear barren of stars. With a little patience, observing effort, and a knowledge of where to look, you'll find Neptune in no time. Even at the darkest sites, magnitude 7.9 Neptune requires optical aid to observe. Binoculars or telescopes are suitable to easily locate and identify the planet in the tail of Capricornus, the Sea Goat. Once the two tail stars of Capricornus are located then we can find Neptune about 2° from gamma Cap, Nashira.

To get your bearings, locate Deneb Algedi (delta Cap) & Nashira, the trailing pair of stars that appear nearly horizontal when Capricornus rises in the East. If you don't see them immediately look closer to the horizon where a bold star, Fomalhaut, shines brilliantly in soliloquy. Scan your bins in a one o'clock direction across 21° of the sky, there you'll see the pair of stars outshining any others in the area. In the field of view, note the trail of three mag 5 stars in a southeast to northwest line just north of Deneb Algedi. To the west of that line, I identify the triangle of fainter stars.

At a distance of 4.4 billion km (2.7 billion mi) from Earth, Neptune's size only subtends an angle of 2.3 arc seconds, an angular diameter the same size as Jupiter's moon Io. In binoculars the reward is finding and observing the most distant planet of the Solar System. In a telescope at 100x magnification there is no appreciable features to observe other than it may appear as a tiny disk rather than a star to the keen observer.

In Peter Grego's Solar System Observer's Guide, there is a brief description of Jupiter occulting Neptune during Galileo's time and how the immersion took more than a half hour to complete. One can easily appreciate this fact and the apparent size of Neptune in a telescope by observing the ingress of an Io transit across Jupiter. Away from the planet, Io looks like another bright star, but as it approaches and ingresses the planet one can absolutely see the diameter of this moon.

did i have a chance?

Session name: 20070119.1650

This goal of this session was to observe the 18 hour 10+ minute waxing crescent moon. Did I have a chance? Not the slightest - a deck of clouds covered the horizon from as far north as I could see past west, all the way down into the south. From what I could tell Sun set further north of Statue of Liberty, but it was cloaked beneath that thick, dark quilt.

The Sun set 4:57 EST. The sky clear above 20°. My hopes that this would drop down to 2° were unrealistic. With fist extended at arm's length I looked for Mercury's flame. Extending pinky and thumb, keeping my hand twisted on 10:30-4:30 line I searched for Venus. With handheld bins I scanned above the horizon looking for each. The cloud deck climbed too high in the sky. Venus, at this time, was to be a bit better than 15° in altitude.


Civil twilight began at 5:27 EST. As I swept the 7.5° binocular field of view along the horizon and ogled Lady Liberty, a brilliant light appeared higher in the sky. Venus at 11° was ablaze and stayed in the clear for about 2 minutes. I looked higher in the sky where the clearing continued. Hyades and Pleiades were visible naked eye, contrasted on a darkened turquoise velvet. While struggling with the gusty wind trying to turn the pages, hurried notes were scratched in the logbook. I looked back up to take a count of the how many Pleiades I could count but the show was over. It was only moments.

Off to moonwatch to file a report and tally my scorecard at 0-1.

not my time with McNaught

I missed the whole McNaught thing, observing wholly on the Internet.

This past Tuesday (1/17), Ben a fellow TotL'er issued an unexpected invite to observe daytime McNaught. I was sort of caught off guard not knowing where the comet was or if it was daytime object. Work has occupied a better part of my days that I didn't think I could steal away at lunch. As luck would have it, time freed up and I met Ben at Bryant Park. He had his TV-76 and I with my Takahashi bins.

In short, Bryant Park was not an agreeable place since the horizon consists of rooftop cornices rising easily to 30° in the lower parts. Tree branches confused the field of view with the unfocused shadows tangled with the bluish, white sky. Ben & I tried from various spots with the park but we agreed that if it was visible it was below the rooftops.

Kin would report later in the day that he was unable to see it in binoculars from Union Square Park. I assume his horizon was better.

When we abandoned that hunt, our attention turned to Venus. In the scope, binoculars, and fleetingly naked eye we stood and observed Venus while talking of old & current times. I didn't turn my attention to Mercury and I pretty much ignored the Sun, using our star as a landmark to measure off to Venus - almost a full handspan, pinky to thumbtip (then curl thumbtip in to subtract 2°) separation.

I have missed events in the past primarily due to weather. This year it was due to schedule and priorities - hmmmm.