Finally, the next full moon on May 24 should prove to be quite spectacular with a noticeable ‘mega-moon’ effect, when the moon appears to be somewhat larger than normal.
These events occur when the moon is at ‘perigee’ and therefore actually closer to the Earth.
With the fractionally larger moon looming large over the horizon, the impression is further enhanced by the ‘Ponzo’ effect, a deep rooted human survival mechanism which coupled with our perception of the shape of the sky as being a flattened, not hemispherical dome, give rise to the ‘moon as big as a pizza’ illusion.
This of course is a trick of the brain. Bizarrely the illusion seems to disappear when you look at the full moon rising with your head between your legs. If you miss this month’s ‘mega moon’ you will not have to wait long, the full moon on June 23 will appear even larger!
Time once again to look ahead at some forthcoming celestial highlights. We start with a planetary gathering low in the west as Jupiter; the most conspicuous object in the night sky over the last six months finally departs, but is joined by both Mercury and Venus for a splendid planetary conjunction.
Look for the three planets just above the WNW horizon from tonight until June 3rd. 45 minutes to an hour after sunset. Initially, conspicuous Venus lies to the right of fainter Mercury (both around 4 degrees above the horizon) with Jupiter located upper left.
By the start of June Mercury has overtaken Venus with Jupiter slipping down to the left of them so that they form a triangle. After Jupiter departs elusive Mercury will be visible for around three weeks, being at its brightest at the start of June, but appears highest around the 9th. Use binoculars if you cannot initially spot it with the naked eye. Venus should require little help in identifying, readily visible without any optical aid. View it through a telescope and you should be able to discern that Venus exhibits a phase.
As nautical twilight deepens Saturn becomes the sole bright planet in the night sky. Look for it across in the south to the left of the star Spica (in Virgo) and well below the conspicuous orange hue of Arcturus, the brightest star in the summer night sky. By 11pm Saturn is located due south.
Viewed through a telescope Saturn is an unforgettable vista with the rings favourably orientated. Careful observation will also reveal its major moon; Titan as a speck of light close by.
Our Moon is next closest to Saturn on June 19.
The Twilight Zones
As we hurtle toward summer and nights grow ever lighter, the deepest level of darkness; known as astronomical twilight will be absent until early August. The duration of the three ’twilight zones’ continually change with respect to one another from mid northern latitudes, a fact that is most noticeable around the solstices, particularly the summer solstice.
Using evening as an example, following sunset civil twilight exists until the Sun drops to six degrees below the horizon. After this point normal daytime activities cease to be possible and ‘lighting up’ time occurs.
The next level; Nautical twilight, exists when the marine horizon is no longer apparent, by which time the Sun is around twelve degrees below the horizon. In the sky only the brighter navigational stars are visible.
By the time the Sun drops 18 degrees below the horizon all the fainter stars become visible and astronomical twilight commences (true darkness).
When the northern hemisphere is inclined towards the Sun, as it is for our summer, from the latitude of Whitby civil and nautical twilight levels persist for a substantial period of the night as the Sun’s apparent journey below the horizon is relatively shallow.
Indeed for the summer solstice period even nautical twilight barely exists with the Sun barely dipping 13 degrees below the horizon. The further north one travels the lighter nights become, until at latitude 67 degrees N (the Arctic Circle) twilight is completely absent for the duration of summer. Here from the land of the “midnight sun” stargazing is very much limited, to just one, the Sun itself!
The Celestial Ocean
Constellation recognition becomes increasingly tricky as evenings lengthen and nights grow ever lighter, but by using the brightest stars visible you can navigate around the sky. Some star patterns are always easy to recognise. The Plough for instance is now directly overhead; its outline should be familiar to all.
This famous asterism forms the hindquarters of Ursa Major the Great Bear. Follow the sweep of the stars in the handle and ‘arc to Arcturus’, the brilliant star in Bootes located high in the SE. Then speed on to Spica in Virgo down in the South, passing Saturn en-route. Rising in the NE the sparkling steely blue hue of Vega in Lyra is particularly eye catching, while lower still Deneb in Cygnus follows Vega up. Over in the SW Regulus, in the ‘Sickle’ of Leo is pretty conspicuous.
Three stars associated with the winter sky; Procyon, Castor and Pollux are all about to depart in the west. Another ‘winter’ star, Capella in the constellation of Auriga, located in the NW will however remain, skirting above the N horizon during summer. So far from bringing down the curtain on ‘stargazing’, the milder conditions of early summer nights can actually be better suited for people to become acquainted with the ever-changing aspects of the night sky. Weather permitting that is!
The next scheduled public star parties from the West Cliff, near Cpt Cooks statue are on May 24 and 25 from 9.30pm, weather permitting. All welcome.