This Week’s Sky at a Glance, October 14 – 21 ~by Curt Nason
The planet Uranus is at opposition this Thursday, rising at sunset and sitting high in the sky by late evening. I usually try to observe Uranus and Neptune at least once a year in binoculars or a telescope, often as part of an effort to see all eight planets (Earth is fairly easy) in one night or calendar day. Uranus can be seen with just your eyes around opposition but it requires a dark, transparent sky, good eyesight and knowledge of exactly where to look. Both of these planets are near dim naked-eye stars, making them easier to hunt down. A detailed star map including their locations is essential, such as the one published annually on the Sky and Telescope website.
Uranus is about one degree above Omicron Piscium and is brighter than any star that close, using binoculars, and over the next two months it will move west of that star. Neptune can be found less than one degree below Lambda Aquarii over that time span, much dimmer than Uranus but still brighter than any star within that distance below Lambda. With binoculars, the two planets will resemble stars with, perhaps, a slight blue-green hue and less twinkling. A telescope at moderate to high magnification will expand the planets into discs, which I usually see as pale green for Uranus and pale blue for Neptune. Stars, being at vast distances from us, do not look larger under higher magnification, and using this technique was how these planets were distinguished from stars in 1781 and 1846, respectively.
Uranus and Neptune are nearly twins, with Uranus four times wider than Earth and Neptune just a bit smaller but more massive. They are referred to as ice giants. Although their atmospheres are composed primarily of hydrogen and helium, they also contain frozen water, ammonia and methane. In addition, their interiors are predominantly rock and ices. Methane absorbs wavelengths of light in the red part of the visible light spectrum, passing the shorter-wavelength green and blue light. Methane in the planets’ upper atmosphere is responsible for the colours we see through a telescope.
This Week in the Solar System
Saturday’s sunrise in Moncton is at 7:35 am and sunset will occur at 6:34 pm, giving 10 hours, 59 minutes of daylight (7:39 am and 6:40 pm in Saint John). Next Saturday the Sun will rise at 7:44 am and set at 6:22 pm, giving 10 hours, 38 minutes of daylight (7:48 am and 6:28 pm in Saint John).
The Moon is new on Thursday, making this a great week for autumn deep-sky observing. Saturn continues to awe observers with views of its rings in early evening. Mercury and Jupiter are too low in the west for observing after sunset. Mars is about five degrees above Venus this weekend in the morning sky. Next weekend, look for meteors springing from Orion’s club early in the morning. This minor meteor shower is one of two arising from Halley’s Comet.
International Observe the Moon Night is on Saturday, October 28. Members and guests of RASC NB will have telescopes and binoculars set up at the Irving Nature Park in Saint John for this event on Friday, October 27 from 6:30 pm to 9 pm, with a back-up date of Saturday.
Questions? Contact Curt Nason.
FYI– below is a slide showing the relative size of the planets at a recent Learning the Night Sky astronomy course evening. Uranus and Neptune are the greenish and blueish objects [click photo to enlarge].