This Week’s Sky at a Glance, 2022 September 10 – 17
~by Curt Nason
This is the time of year when the evening sky seems static; the stars appear to be in the same place night after night in twilight. As you can see below, the Sun sets about two minutes earlier each evening. With reference to the stars Earth rotates once every 23 hours, 56 minutes and 4 seconds: a sidereal day. But since our clocks are based on a 24-hour mean solar day rather than the sidereal day, the stars rise about 4 minutes earlier each evening. The rate of earlier sunsets this time of year cancels half of that. Although the stars rise earlier we also see them sooner. That is a bonus because many of the finest objects to observe in a telescope are prominent now, particularly the Milky Way.
The opposite occurs in spring when the later sunsets add to the earlier rising of stars. The constellations seem to fly past over a month or two, much to the chagrin of those who delight in observing the distant galaxies that abound in those constellations. Earth’s motion around the Sun results in many of the constellations being seasonal. For example, we currently see Orion in the southeast before sunrise. Come January it will be there after sunset and stick around in the evening sky until mid-spring. Those constellations near the north are circumpolar, meaning they never set and we see them year round. There are 22 constellations in the southern hemisphere sky that we see no part of at all from New Brunswick.
This Week in the Solar System
Saturday’s sunrise in Moncton is at 6:51 am and sunset will occur at 7:40 pm, giving 12 hours, 49 minutes of daylight (6:56 am and 7:44 pm in Saint John). Next Saturday the Sun will rise at 6:59 am and set at 7:26 pm, giving 12 hours, 27 minutes of daylight (7:05 am and 7:31 pm in Saint John).
The Moon is full this Saturday, the Harvest Moon as it is the full Moon nearest the autumnal equinox. Saturn is at its highest and best for observing around 11:15 this week while, nearing opposition, Jupiter rises shortly after sunset. On Thursday telescope or binocular users might see Jupiter’s moon Europa emerge from behind the planet at 10:50 pm, and an hour later see Io disappear into Jupiter’s shadow on the opposite side. Over the next month Mars will move eastward from the V-shaped face of Taurus the Bull to its horn tips, seen best high in the morning sky. Venus and Mercury are heading sunward from opposite sides, and they will cross paths near month’s end in the morning sky but too close to the Sun for viewing,
Questions? Contact Curt Nason.