April 17, 2014

Astro-Event(s): Scoping out the Outer Solar System Action.

All Hail the Harvest Moon!

(Photo by Author).

It’s great to have bright planets lined up in the dusk sky. With the start of school star party season, it gives us diligent ‘scope operators something bright to aim at, even from the most light-polluted of school basketball courts.

The trouble this week is, we’re once again into a stretch where no planets are favorably placed for evening observation; Venus is high in the morning sky, Jupiter doesn’t reach opposition until December, and Mars, Saturn & Mercury all disappear swiftly after sunset. Even the angle of the dusk ecliptic seems to be conspiring against us, as its shoved unfavorably down along the horizon for mid-northern latitude observers…

But have no fear. The kids want planets, and we give ‘em planets. In addition to a waxing gibbous Moon, three outermost worlds in our solar system lay in favorable positions for observation this week, and near bright targets to boot.

The visibility cone for the lunar occultation of Beta Capricorni.

(Created by the Author using Occult

But first up, the 76% illuminated waxing gibbous Moon occults the wide +3 magnitude double star Beta Capricorni on the morning of September 25th at ~7:05 UTC for observers in the United States southwest. In addition to having a +6 magnitude companion 3 arc minutes from the primary, Beta1 Capricorni is also a close spectroscopic trinary star system. This will be a great one to catch as the dark limb of the Moon covers the pair.

Now, about those planets. Uranus reaches opposition in the constellation Pisces on September 29th. Fans of this space will recall our handy finder chart to spotting those elusive Uranian moons… break out the Shakespeare, as many of these worldlets are all named after characters in A Midsummer Night’s Dream. Uranus shines at magnitude +5.7 and is about 3.7” arc seconds across, just enough to look like a small green disc thru a telescope at moderate to high power. Did you know that amateurs have actually recorded detail on this tiny world? Wow! What high times of astro-imagining to we live in, indeed!

Uranus has been steadily pulling away from the +5.8 magnitude star 44 Piscium after a close pass this weekend; its current position is;

Right Ascension: 0 Hours, 26.0’

Declination:+1° 59.3’


Said Moon also reaches Full phase on the same day as the Uranian opposition at 23:19 EST, or 3:19 UTC on Sunday, September 30th. Being the closest Full Moon to the September Equinox, this is known as the Harvest Moon. Note how the Moon seems to “linger” from night to night, rising less than 30 minutes apart on successive evenings. Again, this is because the ecliptic (and the rough path of the Moon, which is very “ecliptic-like” in 2012) is very shallow to the horizon. More obscure names for the Harvest Moon include the Singing, Blue Corn, Wine, and (we’re not making this up!) the Elk Call Moon.

Casting our eyes further out, two other solar system residents pass nearby guide posts to help locate them; Pluto & Neptune are both near relatively bright stars on September 30th. +14th magnitude Pluto currently sits in the star rich fields along the general direction of the galactic core in the constellation Sagittarius. In fact, Pluto has yet to complete even half of an orbit around the Sun in its 248+ year orbit since its discovery by Clyde Tombaugh in 1930 in the constellation Gemini! Would we have discovered Pluto in later decades against such star-rich fields if Tombaugh hadn’t caught it first? In fact, such a background region is making it problematic for researchers to spot a potential secondary target for NASA’s New Horizons spacecraft after it passes Pluto in 2015. Want to help? Signup and start looking for KBO’s with the citizen science program known as Ice Hunters. Interestingly, a possible target for Pluto was mentioned in a paper released last week, Plutino 15810 (1994 JR1).

Pluto’s position is currently;

Right Ascension: 18 Hours, 29.7’

Declination: -19° 40.6’

The planet/dwarf planet/plutoid etc. Pluto lies 7’ from the 8th magnitude star HD 170120 on September 30th and only a degree from the open cluster M25 for the remainder of 2012.

Neptune the night of September 30th…

(Created by the Author using Starry Night & Paint).

The planet Neptune is also well placed for observation as September draws to a close. The +7.8 magnitude ice giant is located within 2.25° degrees of the +4.3 magnitude star Iota Aquarii & less than 0.5° degrees from 38 Aquarii on the night of September 30th… if you’ve never caught Neptune, this coming weekend is great time to try. I’ve shown it to folks at star parties before, and while the 2.3” disc blue-grey disc is not visually spectacular, the story of the 1st planet discovered after systematic search is!

Neptune’s position this week sits very near;

Right Ascension: 22 Hours 12.3’

Declination: -11° 46.2’

Finally, if you’re up past local midnite, be sure to check out the planet Jupiter. Word on the astro-street is that the Northern Equatorial Belt is back in business, & in active and splendid form. You’ll recall that there was an impact seen on the NEB a few weeks back, and the SEB has just come back into view last year after one of its unpredictable vanishing acts in 2010. Jupiter is aways an active world to examine, and will soon break the drought of naked eye star party planets when it passes opposition on December 3rd, 2012!



  1. [...] 25th: Moon occults the star Beta Capricorni at 8:00 UT as seen from the southwestern [...]

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