This Week’s Sky at a Glance, 2020 May 23 – May 30

By 10 pm the zigzag constellation of Draco the Dragon is halfway up the northern sky to the right of the Little Dipper. Draco’s tail is a line of stars between the Big and Little Dippers. One of those stars is Thuban, which lies between the bowl of the Little Dipper and the middle of the Big Dipper’s handle. About 5000 years ago, when the Egyptian pyramids were built, Thuban was the North Star and entrances to the pyramids were designed with a descending passageway aligned to this star. Coincidentally, the inner two stars of the Big Dipper’s bowl point to Thuban, just as the outer pair points toward Polaris.

From the tail, Draco arcs around the bowl of the Little Dipper and then curves back toward Hercules, with its head being a quadrilateral of stars by the strongman’s foot. The two brightest stars in Draco’s head, Eltanin and Rastaban, are its eyes. They are the brightest and third brightest of the constellation. The faintest of the four is a treat in binoculars, showing matching white stars that resemble headlights or cat eyes. In mythology, the dragon was one of the Titans, rivals of the Olympians. In one of their battles, Athena slung the dragon high into the northern sky. Writhing to right itself, it struck against the northern sky and froze in that position.

This Week in the Solar System

Saturday’s sunrise in Moncton is at 5:37 am and sunset will occur at 8:54 pm, giving 15 hours, 17 minutes of daylight (5:45 am and 8:56 pm in Saint John). Next Saturday the Sun will rise at 5:32 am and set at 9:01 pm, giving 15 hours, 29 minutes of daylight (5:40 am and 9:03 pm in Saint John).

The Moon is at first quarter next Friday, giving spectacular views of craters and mountains all week in a telescope or binoculars. This Saturday around 9:30 pm look for the slim crescent Moon a binocular width below and slightly left of the crescent Venus, with Mercury about half a binocular field to the upper left of Venus. This will be your last week to see Venus in the evening sky for the rest of the year. Jupiter and Saturn are in great position for early morning observing in the south, while reddish Mars brightens in the southeast.

With astronomy meetings and outreach activities on hold, you can watch the local Sunday Night Astronomy Show at 8 pm, and view archived shows, on YouTube. This week’s topic will be telescope accessories.

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

This Week’s Sky at a Glance, 2020 May 16 – May 23

In the second century BC 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 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 magnitude 3 star.

For many of us, the faintest star we can detect with the naked eye in a reasonably dark sky is sixth magnitude (commonly just 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 -2.4 and Venus is -4.3. The full Moon is mag -12.6, approximately 400,000 times fainter than the Sun at -26.7. A first magnitude star is brighter than mag 1.5, a second magnitude star shines between mag 1.5 and 2.5, and so on.

These brightness values are for the apparent magnitude of a star, as we see them when they are highest in the sky. At lower altitudes the atmosphere will absorb some of the starlight, making them appear dimmer. Astronomers call this effect extinction. The apparent magnitude of a star depends on its size and temperature, and also on its distance from us. A doubling of distance reduces the brightness by a factor of four, and ten times the distance by a factor of 100. Therefore, if one star is ten times farther than a mag 3 star of equal size and temperature, it would be at mag 8 and we would require binoculars to see it. There is nothing like an astronomy lesson to brighten your day.

This Week in the Solar System

Saturday’s sunrise in Moncton is at 5:45 am and sunset will occur at 8:46 pm, giving 15 hours, 1 minute of daylight (5:52 am and 8:49 pm in Saint John). Next Saturday the Sun will rise at 5:37 am and set at 8:54 pm, giving 15 hours, 17 minutes of daylight (5:45 am and 8:56 pm in Saint John).

The Moon is new next Friday, a great time to take advantage of mostly contrail-free skies to hunt down distant galaxies with a telescope or binoculars. Mercury and Venus approach each other after sunset, being within a binocular view for the latter half of the week. Mercury is less than a thumb width below Venus on Thursday and to its left on Friday. Jupiter and Saturn are in great position for early morning observing, as they slowly start to move apart. Mars is starting to brighten as we are catching up to it, and by the end of the month it will be as bright as the stars Vega and Arcturus.

With astronomy meetings and outreach activities on hold, you can watch the local Sunday Night Astronomy Show at 8 pm, and view archived shows, on YouTube at: https://www.youtube.com/channel/UCAEHfOWyL-kNH7dBVHK8spg

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

Share
Scroll to top