This Week’s Sky at a Glance, June 16 – 23 ~by Curt Nason
Seasons are the result of Earth’s rotational axis being tilted about 23.5 degrees off the vertical with respect to its orbit. The first day of astronomical summer occurs this Thursday. The “astronomical” qualification is used because meteorologists have taken to confusing people with meteorological seasons based on temperatures. Meteorological summer in the northern hemisphere includes June, July and August because they have the highest average temperatures for the year. Anyone who has lost crops this month due to frost will not be in total agreement with that.
On the summer solstice, the Sun rises and sets at its most northerly points on the horizon. For those of us at 45 degrees latitude, at midday (1:21 pm in Moncton) the Sun is 90 – 45 + 23.5 = 68.5 degrees above the southern horizon, at its highest for the year. If we lived at latitude 23.5 degrees the Sun would be directly overhead at midday on the solstice. Several millennia ago the Sun was “in” the constellation Cancer on the solstice, hence that latitude is marked on maps as the Tropic of Cancer. The dim constellation does resemble a crab somewhat, but there is speculation that the Sun’s forth and back movement along the horizon at that time of year was reminiscent of a crab’s sidewise walk.
Prior to being in Cancer at the start of summer, the Sun was in Leo. Lions tended to gather by the Nile in the dry season around the solstice. Now the summer solstice point on the ecliptic, the Sun’s path through the constellations, lies in Taurus, just within its boundary with Gemini. The roaming solstice is due to Earth’s axis wobbling like a top, making one revolution every 25,800 years in what we call the precession of the equinox. Enjoy your summer, whenever it starts.
This Week in the Solar System
Saturday’s sunrise in Moncton is at 5:27 am and sunset will occur at 9:12 pm, giving 15 hours, 45 minutes of daylight (5:35 am and 9:14 pm in Saint John). Next Saturday the Sun will rise at 5:28 am and set at 9:14 pm, giving 15 hours, 46 minutes of daylight (5:36 am and 9:15 pm in Saint John). Summer solstice occurs at 7:07 am on Thursday.
The Moon is at first quarter on Wednesday, giving great views in a telescope throughout the week. If you can spot it in the east this Saturday morning, look for Venus within a binocular field above it. If you are successful with that, try for Venus without the binoculars. After twilight on Tuesday look for M44, the Beehive Cluster, just below Venus. Jupiter is situated for great observing in the evening and it will get extra attention on June 23 with the Moon nearby. A binocular view of Jupiter will show its line-up of moons and the double star Zubenelgenubi to its lower left. Saturn rises around 9:30 pm and a late evening view of it in binoculars will include the globular cluster M22 to its lower left. A dust storm has kicked up on Mars – hopefully, it will dissipate soon and not obscure features of the Red Planet like one did in 2001.
The The first RASC NB star party of the year takes place at Kouchibouguac National Park on June 15-16. The last RASC NB meeting until September takes place on June 23 at 1 pm in Moncton High School. All are welcome.
Questions? Contact Curt Nason.