Advanced VX Computerized Telescopes

This Week’s Sky: May 23 – 30

A close call with Mars, and a last-quarter Moon.


Globular cluster M13 is one of the May night sky’s prime attractions. Courtesy Howard Trottier/SFU

All Week

South, end of twilight

The view facing due south at the end of evening twilight.

The early evening sky is full of bright delights this week. Face south at the end of twilight and you’ll be greeted by a collection of luminaries that inculdes a trio of planets and a quartet of first-magnitude stars. The planets Jupiter and Mars are the most conspicuous beacons and shine at essentially the same brightness (magnitudes –2.1 and –2.0 respectively). Jupiter is positioned high in the west while Mars resides low in the south in Scorpius. The red planet’s altitude is greatest around 1 a.m., local daylight time — and that’s the best time to train a telescope on it. Just a little east of Mars is Saturn, which reaches the meridian about an hour later. At magnitude 0.0, the ringed planet is noticeably dimmer than its orange neighbour.

May 29

This morning the Moon reaches last-quarter phase at 8:12 a.m., EDT.

May 30

Mars Opposition Diagram

The minimum distance in astronomical unites (AU) and maximum disc size in arc seconds (“) are given for each opposition. SkyNews diagram

Today Earth finally catches up to Mars and the two worlds are at their closest, separated by a distance of 75,281,058 kilometres. That means the red planet is as big as it’s going to get this apparition, spanning 18.6 arc seconds. The Martian disc won’t achieve this size again until June 19, 2018.

For more on viewing Mars, visit here and turn to page 33 of the current issue of SkyNews.

Weekend Stargazer

M13 chart

Finder chart for globular cluster M13 in Hercules.

The evening sky is moonfree over the May 27 – 29 weekend, which makes it a good one for catching a few deep-sky treats. However, since the summer solstice is less than a month away, the nights are rapidly growing shorter. Observers at the latitude of Toronto, Ontario, enjoy about 3½ hours of astronomical darkness, and those along the 49th parallel have to make do with less than 2 hours. But for sky watchers farther north (at the latitude of Edmonton, Alberta, for example), there is no astronomical night this weekend.

Take advantage of whatever darkness you have to do some globular cluster hunting. You can start with one of the most famous: M13 in Hercules. It’s in prime position at the moment and is regarded by many as the very best globular for northern-hemisphere observers. (I personally don’t agree — M22 in Sagittarius seems more impressive to me.)

M13 bino view

The field of view for 10×50 binoculars is indicated by the blue circle. Photo courtesy Gary Seronik

Home to a half million stars, M13 is faintly visible to the unaided eye under dark skies. In binoculars it looks like a fuzzy “star,” but the globular really comes into its own in a telescope — the bigger the better. A smallish instrument (under 3-inches aperture) provides a pleasing image that will reveal a few cluster members popping fleetingly into view. But in a mid-size scope, M13 is truly a sight to behold. Uncountable stellar points are arrayed against a glowing core of densely packed starlight. Try different magnifications to find one that best shows the cluster in your telescope. High power will reveal individual stars best, but lower magnification shows M13 situated nicely within its star field. Both views are splendid.

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