This Week’s Sky at a Glance, 2019 June 22 – 29 ~by Curt Nason
After watching the sky for many decades it is nice to see something new. Several people noticed shiny blue clouds stretching northwest to north on the evening of June 12, about an hour after sunset. Possibly, this was the first time noctilucent clouds (NLC) have been seen in southern New Brunswick.
NLCs form in the earth’s mesosphere at an altitude of about 80 kilometres. Water molecules rising to that height attach to smoke particles from disintegrating meteoroids and freeze. Sunlight from below the horizon refracts through the ice clouds, scattering the blue portion of the sunlight back toward the planet. This phenomenon was first seen in polar regions in 1885 after the eruption of the Krakatoa volcano spewed water vapour and gases such as methane high into the atmosphere. In recent decades the NLCs have been spotted at latitudes increasingly farther from the poles. Also, the periods when they are visible are stretching beyond a month either side of the solstices.
Studies of historical NLC reports suggest that these increases in range of latitude and time are related to both global warming and the 11-year sunspot cycle. Methane in the mesosphere undergoes a chemical reaction that produces water vapour, adding to the water vapour rising that high in warmer weather. During the minimum of the sunspot cycle, which we are currently experiencing, the reduced solar activity results in lower levels of the ultraviolet light that breaks up water molecules. Two days after seeing the NLCs in New Brunswick, they were seen at a record low latitude just north of Los Angeles. Satellite measurements of polar atmospheric water vapour showed higher than usual levels this year, which are now decreasing.
Keep an eye out for these electric blue clouds in the northwest about an hour after sunset or in the northeast before sunrise. To get an idea of what to look for you can see pictures of NLCs on the website spaceweather.com, which is the source of my information above.
This Week in the Solar System
Saturday’s sunrise in Moncton is at 5:28 am and sunset will occur at 9:14 pm, giving 15 hours, 46 minutes of daylight (5:36 am and 9:15 pm in Saint John). Next Saturday the Sun will rise at 5:30 am and set at 9:14 pm, giving 15 hours, 44 minutes of daylight (5:39 am and 9:16 pm in Saint John).
The Moon is at third quarter on Tuesday, rising at 1:40 am and setting at 1:35 pm. Jupiter is at its highest and best for observing around midnight, and telescope users might see the shadow of its moon Io crossing the planet’s atmosphere late Thursday evening. Saturn is rising around 10 pm this week. Mercury is at greatest elongation from the Sun on Monday and remains within a binocular view to the left of dimmer Mars. Venus rises around the beginning of civil twilight in the morning.
Questions? Contact Curt Nason.