Sky at a Glance 2022 May 7 – 14

Photo showing locations of Mag 1 stars Vega, Arcturus and Spica.

This Week’s Sky at a Glance, 2022 May 7 – 14 ~by Curt Nason

In the second century BCE the Greek astronomer Hipparchus of Nicaea ranked the stars according to their brightness in six categories called magnitudes (for greatness). The 20 brightest stars were rated first magnitude and the faintest stars were sixth magnitude. This system was retained for two millennia and standardized in the 19th century when much fainter stars were being detected by telescopes and astrophotography. English astronomer Norman Pogson devised a logarithmic system whereby five magnitudes was a difference in star brightness of exactly 100 times. With this system, a magnitude 1 star is about 2.5 times brighter than a magnitude 2 star, and that one is 2.5 times brighter than a star of magnitude 3.

For many of us, the faintest star we can detect with the naked eye in a dark sky is sixth magnitude (commonly called mag 6). Vega, the fifth brightest star, is mag 0, slightly dimmer than Arcturus and slightly brighter than Capella. With the ability to measure the exact brightness of stars, their magnitudes are often recorded to one or two decimal places, and negative values are used for very bright objects. Sirius is mag -1.4; Jupiter is currently mag -2.1 and Venus is -4.1. The full Moon is mag -12.6, approximately 400,000 times fainter than the Sun at -26.7. A first magnitude star, of which there are 22, is brighter than mag 1.50; a second magnitude star shines from mag 1.50 to 2.49, and so on.

This Week in the Solar System

Saturday’s sunrise in Moncton is at 5:57 am and sunset will occur at 8:35 pm, giving 14 hours, 38 minutes of daylight (6:04 am and 8:37 pm in Saint John). Next Saturday the Sun will rise at 5:47 am and set at 8:43 pm, giving 14 hours, 56 minutes of daylight (5:55 am and 8:46 pm in Saint John).

The Moon is near the Beehive star cluster in Cancer on Saturday, International Astronomy Day, and it is at first quarter on Sunday. It passes near Regulus in Leo on Monday and Spica in Virgo on Friday, two of the four first magnitude stars that are occasionally occulted by the Moon. Get ready for a total lunar eclipse at the end of next weekend. Mercury is stationary on Tuesday, after which it moves westward relative to the stars and returns to the left of the Pleiades next weekend. Saturn rises around 3 am this weekend, followed by Mars an hour later and then Jupiter and Venus. Venus rapidly pulls away from the planetary pack while Mars speeds toward a close conjunction with Jupiter near the end of the month.

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.

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