Dance of the planets heralds summer line-ups

Since June marks the start of our summer, let the line-ups begin…

The sixth month by its very name has a planetary association. The Romans of antiquity, subscribing to Greek mythology, named their supreme god Jupiter, with the queen of the gods called Juno – from whence comes the month’s name. In the interest of domestic harmony one would expect Jupiter to feature prominently this month. However, this June sees Jupiter disappearing behind the Sun with the planet reaching solar conjunction on June 19. This means Earth-Sun-Jupiter form a line with the Sun occupying the middle position. When Earth occupies the between spot of this three-member line Jupiter would be in the opposite direction from the Sun and termed as being in opposition.

Mars went into solar conjunction in April and will remain behind the Sun through June. At the end of May, Mercury, Venus, and Jupiter will be as close together in the evening sky as can be seen by the unaided eye until 2026. The closest grouping will form a tight triangle (about two finger-widths) on May 26, appearing low in the west at sunset.

Since Mercury is the planet closest orbit to the Sun, view it either just before sunrise or just after sunset. It is in the optimal viewing location when the planet is at its greatest western, or greatest eastern elongation, respectively. Astronomical elongation refers to the greatest angle between the Sun and a planet as measured from the Earth-Sun line. Mercury will be at its highest angle (furthest east) above the western horizon on June 12, where it will sit approximately 24 degrees high in the evening sky, and set about 90 minutes after the Sun. On June 20 Mercury and Venus will be about 2 degrees apart in the west at sunset, as Mercury starts back toward the Sun from our perspective.

The full moon falls on June 23 and because it coincides very closely with perigee – the Moon’s closest approach to Earth – it will actually be the largest and brightest full moon of the year. The general astronomical term for objects oriented in a line is syzygy. Since the full moon takes place very close to the time of the Moon’s closest approach to Earth, it is termed a perigee-syzygy. Figure 1 shows the geometrical particulars for the Moon’s orbit. Keep in mind that the Moon is ‘new’ when it lies between us and the Sun, and all the sunlight, ironically enough, falls on the Moon’s so-called dark side – the side out of our sight. When the Moon is halfway through its orbital cycle it is ‘full’, with all the incident sunlight reflected from the entirely illuminated face we view. At both full moon and new moon the Earth-Moon-Sun system is in syzygy, but when the Moon is full the Earth holds the position between the Moon and Sun.

For anyone interested in astronomy, the local chapter of the Royal Astronomical Society will be meeting Friday, June 14 at 7:30 pm at the Sunshine Coast Art Centre in Sechelt. Because of the long summer day, if the sky is clear, a couple of scopes will be set up for solar viewing outside the Art Centre. As well, those interested in stargazing should feel free to drop by the ‘astro-café’ at Pier 17, Davis Bay, on Friday, June 21 – the first evening of summer – where local club members will meet for coffee and chat at 8:30pm, and set up telescopes for viewing after sunset, weather permitting. The Sunshine Coast Astronomy Club website is www.CoastAstronomy.ca