Over the last few weeks we have seen a number of interesting phenomena in the skies above us.
Perigee full Moon - the largest and closest full moon for the year appeared on 5 May. Full moons occur when the Moon, Earth and Sun are aligned with the Earth in between the Moon and Sun. For a given month the closest point of the Moon to Earth is called perigee and the farthest is apogee. On 5 May the perigee Moon was 356,955 kms from Earth and on 19 May the apogee Moon was 406,448 kms from Earth. Full and Perigee Moons coincide because their cycles periodically align, the closest Moon for 2013 will occur on 23 June 2013 and the closest for the 21st Century will occur 6 December 2052 when the Moon will be 356,446 kms away from Earth. All full moons bring higher and lower tides than usual but perigee full moons cause the highest and lowest of tides.
Transit of Venus – a transit occurs when a planet appears to travel across the face of the Sun, this can only happen when a planet orbits between the Sun and the Earth – only two planets follow such an orbit – Mercury and Venus. Transits of Mercury are difficult to observe due to the planet's small size, they occur approximately 13 times per century. Transits of Venus are easier to observe but far rarer. Although the Sun, Venus and Earth align in the same direction approximately every 584 days Venus is usually above or below the Sun in the sky so we do not see it track across the Sun. Transits occur in a 243 year pattern of 121.5 and 105.5 years separated by a gap of 8 years, the last transit was in 2004 and the next transit is due on 11 December 2117.
The transit of Venus has a special historical significance for Australians. Captain James Cook and his crew were commanded to take scientists to Tahiti to observe the transit of Venus. The transit was to be observed by many scientists watching from multiple locations around the world and by calculating and comparing the time taken for Venus to travel across the Sun it was hoped that this measurement could provide the basis for calculating astronomical distances. Once the observations of the transit of Venus were complete James Cook embarked on his voyage of discovery on the Endeavour which would lead him to Australia and New Zealand.
Lunar Eclipse – a partial lunar eclipse occurred on 4 June. Partial eclipses occur when the Earth slides between the moon and Sun, and casts a shadow over the moon. In this lunar eclipse approximately one third of the moon was covered by the Earth's umbral shadow. The next lunar eclipse is due on 28 November 2012.