Photo of lunar eclipse taken at Charlottetown
On the evening of Sunday, Sept. 27, weather permitting, we here on the Island will experience one of the most thrilling celestial events — a total lunar eclipse.
This eclipse will be even more spectacular due to the fact that it will be the eclipse of a supermoon. A supermoon is when a full or new moon occurs when the moon is at perigee, the moon’s closest approach to Earth in its monthly orbit. September’s supermoon (the second of three in a row from August to October 2015) will be the biggest eclipsed supermoon ever, as this year’s closest lunar perigee will occur about one hour before mid-eclipse. The moon will be noticeably larger and brighter.
As sunlight streams passed Earth, it casts a two-circle, bulls-eye-shaped shadow into space. The inner, darker shadow is called the “umbral” shadow (or “umbra”), while the dimmer, outer shadow is referred to as the “penumbral” shadow (or penumbra). The lunar eclipse will begin at approximately 9:40 p.m. on the evening of Sept. 27, when the leading edge of the full moon first enters the penumbral shadow. It won’t be until the moon is about half-way into the penumbral shadow that we will begin to notice any change in the brightness or colour of the moon’s surface, and even then, it will only be a light shading. The second part of the eclipse (called a “partial” eclipse) occurs around 10:07 p.m., when the moon begins to enter the umbral shadow. As it enters the umbral shadow, the moon’s surface should take on a definite orangish-red colour. This colouration is due to sunlight filtering through the Earth’s atmosphere around the entire planet, with only the red end of the colour spectrum being bent and appearing on the moon’s surface. The exact tint of orange and /or red depends on how much volcanic dust or haze is in the Earth’s atmosphere at this time - the more dust or haze, the redder the colour of the moon’s surface.
It will take approximately an hour for the moon to slide totally into the umbral shadow, with the last, trailing edge of the moon entering the umbral shadow at approximately 11:11 p.m. This is when the moon is in total eclipse. Totality lasts until approximately 12:23 a.m. (on Sept. 28), when the leading edge of the moon leaves the umbral shadow and enters the penumbral shadow (creating another “partial” eclipse). The moon then slides through the penumbral shadow, leaving the shadow entirely around 1:55 a.m., at which time, the lunar eclipse is over.
Hopefully, the weather will co-operate as the next total lunar eclipse will occur in January 2018, and we here on P.E.I., will not be able to see it.
Planet-wise, only two bright planets will be visible in the evening sky in September. Mercury will appear very low in the WSW during the first half of the month, setting about 50 minutes after the sun. Saturn will sit fairly low (about 20 degrees above horizon) in the SW all month. Shining at mag. +0.5, it will set about three and a half hours after the sun at the start of month, and about two and a half hours after sunset by month’s end. Look for the waning, crescent moon sitting to the upper right of Saturn about an hour after sunset on the evening of Sept. 18.
Venus, the “morning star” will climb noticeably higher in the pre-dawn with each passing week in September. Shining at mag. - 4.8 during the latter half of the month, it will be a brilliant sight. Look for the thin, crescent moon to the left of Venus on the morning of Sept. 10 about 1 hour before sunrise. As September begins, Mars sits higher than Venus in the pre-dawn sky, but as Venus climbs higher each morning, it will shift to the lower left of Venus (about a fist’s width at arm’s length). Jupiter (mag. - 1.7) rises due east before sunrise, appearing to the lower left of Venus.
The autumnal equinox, the official start of autumn here in the northern hemisphere, occurs on Sept. 23 at 5:21 a.m.
September’s full moon is known as the harvest moon as this is the time of year farmer begin to harvest their crops. This full moon is the biggest of the year, as it occurs at the moon’s perigee or closest approach to Earth on the night of the 27.
Until next month, clear skies.
Glenn K. Roberts is a member of the Charlottetown Centre of the Royal Astronomical Society of Canada (RASC). His column appears in The Guardian once a month. He welcomes comments from readers. Anyone who would like to comment on his column is encouraged to email him at firstname.lastname@example.org.