This Week’s Sky at a Glance, 2022 June 11 – 18 ~by Curt Nason
Globular clusters are among the oldest and largest objects associated with our galaxy, being about 12 billion years old and containing tens to hundreds of thousands of stars packed into a compact sphere. There are more than 150 globulars orbiting in the halo of the Milky Way galaxy, and many more are known to be orbiting larger galaxies like M31 in Andromeda. Many can be seen in binoculars as a fuzzy patch of light, perhaps resembling those little white patches you see below bird feeders. A medium size telescope is able to resolve some of their stars. The larger globulars as seen from a dark location have been described as looking like granules of sugar against black velvet.
Summer is the season for observing globular clusters. M4 is just to the right of Antares in the constellation Scorpius and it is one of the closest globulars at 7000 light years. M13 in the Keystone of Hercules is relatively close at 22,000 light years. One that would outshine M13 if it were higher in our sky is M22, just left of the lid of the Teapot in Sagittarius. Another easy target is M3, located halfway between Arcturus and Cor Caroli, the brightest star in the small constellation Canes Venatici below the handle of the Big Dipper. Two other standouts are M92 in Hercules and M5 in Serpens.
From a dark sky, many dimmer globulars can be picked out in the region of Sagittarius and Ophiuchus. The concentration of globular clusters in this region of sky is not by accident, and it played a role in another lesson of humility for humanity. Harvard’s Harlow Shapley studied globular clusters a century ago and noticed that most were located around Sagittarius. If they were evenly distributed around the core of our galaxy, as believed, then the centre of the galaxy must lie in that direction. Just as Copernicus and Galileo demoted Earth from the centre of the solar system, Shapley showed that the Sun was not at the centre of the Milky Way.
This Week in the Solar System
Saturday’s sunrise in Moncton is at 5:27 am and sunset will occur at 9:10 pm, giving 15 hours, 43 minutes of daylight (5:36 am and 9:11 pm in Saint John). Next Saturday the Sun will rise at 5:27 am and set at 9:13 pm, giving 15 hours, 46 minutes of daylight (5:35 am and 9:14 pm in Saint John).
The Moon is full and near perigee on Tuesday, resulting in extreme tides midweek. Around 11:25 pm on Sunday it occults (passes in front of) Dschubba, the middle star in the arc of three to the upper right of Antares in Scorpius. Shortly after Dschubba reappears from behind the Moon an hour later, Saturn rises in the east. Mercury is at greatest elongation from the Sun on Thursday, making it easier to locate in twilight although using binoculars is recommended at first. This begins a period of two weeks or more when the five naked-eye planets are lined up in their order of distance from the Sun: Mercury, Venus, Mars, Jupiter and Saturn. I think that is a sight worth rising with the rooster.
On Sunday evening at 8 pm, tune in to the Sunday Night Astronomy Show via the Facebook page or YouTube channel of Astronomy by the Bay.
Questions? Contact Curt Nason.