On the 23rd, the “ice giant” Uranus will be visible all night, as it rises when the sun sets (hence it is opposite the sun). It will also be at its largest for the year: a diminutive 3.73″ of arc. Due to its distance and close-to-circular orbit, Uranus doesn’t vary that much in brightness over time. It will reach magnitude 5.7 from mid-October through early November before slightly fading to magnitude 5.9 in late March 2019. This makes it a naked-eye target in dark skies and easy to locate in a binocular or finderscope.
With the moon a waning crescent, it is a good time to pick out some faint objects in the sky.
On Friday, September 7th, Neptune rises opposite the sun and is closest to earth. Being in the sky all-night, and at it’s brightest, presents a good opportunity to sight this rarely-seen telescopic planet. Unlike the naked eye planets, you’ll have to crank-up the power to make sure you’ve really found it. Even at 100x it just looks like a magnitude 7.8 star. So don’t expect to see a Voyager 2 quality image through your eyepiece.
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Mars will exceed 24-arc-sec in diameter between July 23rd and August 9th, 2018. This is 97 percent of the maximum of 25.13-arc-sec diameter attained during the last of the ‘favorable’ apparitions, which occurred in 2003.Association of Lunar and Planetary Observers
At the end of this month, on July 27th, Mars will be in opposition and reach its greatest angular diameter — 24.3-arc-seconds — for the year. This is the best opposition since 2003. It’ll be greater than 21-arc-seconds tonight and well worth observing. For an explanation as to why some oppositions are better, what to expect from this year’s event, and accessories to better view and image Mars, see our blog post: Mars Opposition 2018 Preview.
Saturn is in opposition tonight: it glides above the horizon around sunset and will be over 18-arc-seconds in diameter for a few weeks. At about magnitude 0.0, it will pair well with the full moon that accompanies it across the sky this evening.
By the 1970s amateurs had noticed that all 110 Messier objects could be observed at low northern latitudes over the course of a night in mid-to-late March.
You’ve probably heard of Charles Messier’s catalog of celestial deep-sky objects for 18th century comet hunters. When they stumbled upon an unknown faint fuzzy object, they’d consult this list to see if it was a known object. It was first published in 1774 and expanded with help from fellow observers in that century. Astronomers and amateurs in the early 20th Century rediscovered it, added a few new objects, and made corrections. There are now 110 “M” objects in the modern catalog.
Every sky chart labels the location of these objects with the letter “M” and a number. For instance, the brightest Messier is M45 — the famous naked-eye Pleiades open star cluster. A third of the way around the sky you’ll find the dimmest: M95 — a galaxy of magnitude 10 or 11 (depending on the source) in Leo.
Most amateur astronomers will ignore the full moon. The best telescopic observations can be had before and after the moon is full. For instance, when the moon is half-illuminated, at first quarter, as it waxes toward full. Along the night and day terminator line bisecting the moon are the boldly cast shadows of mountains, craters, rilles, and basins. This is where your telescopic lunar observations should begin.