This Week’s Sky at a Glance, 2019 June 1 – June 8

The basis for ranking stars by brightness dates back to the Greek astronomer Hipparchus in the second century BC. He grouped several hundred stars by their apparent size, with the biggest being in the first magnitude group and the faintest to the naked eye being sixth magnitude. Magnitude in this sense means size, and even now many people refer to bright stars as big. The telescope and astrophotography allowed us to detect stars much fainter, and in the 19th century Norman Pogson adapted the old system to a standard. A five magnitude difference was defined as a difference in brightness of exactly 100. Therefore, a first magnitude star is a tad more than 2.5 times brighter than a second magnitude star, about 16 times brighter than a fourth magnitude star, and 100 times brighter than one of sixth magnitude. The scale extends into negative numbers for very bright objects, including planets and a few stars.

Check out a cloudless sky this week when it is dark. The bright star Vega is often regarded as the benchmark, being very close to mag 0 (astronomers usually shorten magnitude to mag). Arcturus is slightly brighter, edging into the negative decimals at mag -0.05. Spica, the brightest star in Virgo, is very close to mag 1 at 0.98. A mag 2 star is Polaris, the North Star, at the end of the Little Dipper’s handle. Obviously, it is not the brightest star as some people believe; it barely makes the top 50. A mag 3 star is Pherkad, the dimmer of the two stars at the base of the Little Dipper. Jupiter is currently near its brightest at mag -2.6, and Saturn is at mag 0.3. By the way, that star we see in daytime is mag -26.75 at midday.

This Week in the Solar System

Saturday’s sunrise in Moncton is at 5:31 am and sunset will occur at 9:02 pm, giving 15 hours, 31 minutes of daylight (5:39 am and 9:04 pm in Saint John). Next Saturday the Sun will rise at 5:28 am and set at 9:08 pm, giving 15 hours, 40 minutes of daylight (5:36 am and 9:09 pm in Saint John).

The Moon is near Venus this Saturday morning, is new on Monday and near the Beehive star cluster on Thursday evening. Mercury sets 90 minutes after the Sun by midweek and can be seen eight degrees above the horizon a half hour after sunset. Watch it and Mars slowly approach each other over the next two weeks. On Tuesday evening, between 9:30 and 10:55, telescope users have the opportunity to see the shadows of Jupiter’s moons Ganymede and Io crossing the planet’s clouds. By midnight later in the week Saturn will be high enough to give a decent view of its rings in a telescope. Venus continues to herald the sunrise by nearly 50 minutes.

The Saint John Astronomy Club meets in the Rockwood Park Interpretation Centre this Saturday at 7 pm. RASC NB members will have telescopes set up for public viewing at the Kouchibouguac Park Spring Starfest on June 7 and 8.

Questions? Contact Curt Nason at nasonc@nbnet.nb.ca

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