This Week’s Sky at a Glance, 2019 June 15 – 22 ~by Curt Nason
It has been said we live in a topsy-turvy world. Actually, we live on one. Earth’s polar axis is tilted to its orbital path around the Sun, leaning just over a quarter of the way from upright to horizontal. At our summer solstice, the north polar axis is tipped toward the Sun and sunlight reaches us at a steep angle with concentrated warmth.
If you note the times of sunrise and sunset over the month you might be surprised to discover the earliest sunrise and latest sunset do not occur on the solstice. Although the most amount of daylight occurs then, we get our earliest sunrise around June 16 and latest sunset around June 26. Earth’s tilt plays a role in that, as does the fact that its orbit is not circular. We are about five million kilometres closer to the Sun in early January than we are in early July. Four centuries ago Johann Kepler showed that planets travel faster when they are nearer the Sun. Have you noticed that the time between the beginning of spring and fall is a week longer than between fall and spring?
We expect the Sun to reach its highest daily position in the sky, the zenith, at midday (noon local standard time, accounting for distance from the centre of our time zone). However, the Sun’s daily north-south movement over the seasons and Earth’s varying speed in orbit make the Sun appear to reach zenith ahead or behind schedule by as much as 16 minutes. Consequently, our 24-hour clock is based on an annual average noon called mean solar time. Sundial aficionados know they have to account for these daily corrections to agree with the clock.
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 9:13 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). The summer solstice occurs on Friday, June 21 at 12:54 pm when the Sun reaches its most northerly position and remains above the horizon for the longest period of the year.
The Moon is full at sunrise on Monday, the Mi’gmaw Trees Fully Leaved Moon. It is near Jupiter on Sunday and near Saturn on Tuesday. Jupiter is now seen low in the southeast in evening twilight, and its atmospheric storm called the Red Spot might be seen with a telescope around 11 pm on Monday. Mercury and Mars will be within the same twilight binocular view all week, crossing paths on June 18 with Mercury just above the dimmer red planet. Saturn rises around 10:30 pm, before the end of nautical twilight, and Venus rises around the beginning of civil twilight in the morning.
Weather permitting, the Ganong Nature Park near St. Stephen will be a hosting a presentation about facts and fantasy of the Moon on Monday at 8:30 pm, followed by an open field hike under the rising full Moon. Admission is by donation.
Questions? Contact Curt Nason.