Planetary Comings and Goings
Conspicuous Venus remains low in the WNW evening twilight sky, gradually sliding down closer to the west horizon by late July.
Saturn resides in the WSW as twilight deepens, visible to the naked eye to the left of Spica, chief star in Virgo. Through the eyepiece Saturn is a glorious sight with the rings favourably orientated.
Look also for its largest moon Titan, visible as a speck of light nearby.
Towards the end of July, Jupiter and Mars become visible in the early dawn sky (4am) over in the ENE.
Mars lies just above Jupiter on the 22nd before Mercury joins the pair for the last two days of July, though it will be quite difficult to pick out just above the horizon.
Noctilucent Cloud Displays
Observers of the late evening twilight sky should remain vigilant as the Noctilucent cloud season reaches a climax in the next few weeks. This particularly beautiful type of cloud formation is seen only at this time of year appearing above the northern horizon, long after sunset, often around midnight.
Shining quite brightly, Noctilucent cloud is filamentary in structure, having a characteristic silvery-blue colour. It forms almost exclusively between latitudes 50 and 60 degrees north, high in the upper atmosphere: 50 miles up- five times higher than normal clouds.
The cloud forms when water vapour condenses at the low temperatures that prevail at such altitudes onto particles suspended in the air. There have been several sightings already this summer, so please do keep watch.
The Celestial Ocean – Late July
The long overdue appearance of fine and settled weather conditions hopefully means that people are more likely to be tempted out for a late evening stroll, allowing the casual observer a better chance to become better acquainted with the stellar summer canopy above them.
One of the first stars to pierce the cloak of dusk lies overhead to the SSE.
This is brilliant steely blue-white Vega in the small but distinctive geometric pattern of Lyra, a striking spectacle when viewed through a telescope. Vega is also the brightest member of the ‘summer triangle’ asterism.
Throughout our summer Vega is outranked only by brilliant orange hued Arcturus in the constellation of Bootes, visible at present high in the lighter SW aspect of the sky.
Situated just 37 lyrs away Arcturus is the closest orange giant type star to ourselves, but would be dwarfed by the deep orange star visible low above the SSW horizon.
Antares is the chief star in Scorpius, one constellation that actually does resemble the creature it is named after, though unfortunately from the UK only the upper half is visible with the majority of the ‘sting’ below the horizon.
Following Scorpius across the S horizon is yet another zodiac star group; Sagittarius part of which resembles the outline of a teapot. If you have a pair of binoculars or a small scope this whole region is a most rewarding destination, (given a clear horizon) full of clusters and nebulae.
The centre of our galaxy lies in the direction of Sagittarius, roughly 27000 light years away.
Somewhat higher in the South and flanked by fainter stars, Altair, in the constellation of Aquila the Eagle marks the southern point of the ‘summer triangle’.
A mere 16 light years away, Altair is nearest of the bright summer stars visible from Britain.
Tracking up from Altair passing the small and distinctive diamond shaped group of Delphinius - the Dolphin and through Sagitta the Arrow, we arrive at Cygnus the Swan also called the Northern Cross.
Cygnus is home to the third member of the summer triangle; Deneb, which marks the tail of the swan. Appearing less brilliant than the other ‘triangle’ stars, in reality Deneb is far more powerful residing over 1700 light years away.
Once nights do become fully dark again (mid August) look for the faint light of the Milky Way passing right through the long axis of the Northern Cross.
The star marking the head of the Swan, Alberio is one of the loveliest double stars in the night sky, a must see object for anyone with a small scope, a golden primary star contrasting beautifully next to a sapphire secondary one.
The area of sky bounded by Scorpius, Aquila, Lyra and Bootes is chiefly occupied two large but mostly ill-defined constellations. West of Lyra sits Hercules best identified by the ‘Keystone’ asterism, while below Hercules the huge dim outlines of Ophuichus and Serpens sprawl.
Look for the pretty circlet of stars between Hercules and Bootes marking Corona Borealis - the Northern Crown. The region below Bootes and the WSW horizon is occupied by Virgo, highlighted by bright Spica.
The familiar pattern of the Plough hangs in the NW, whilst due north brilliant Capella in Auriga is sometimes mistaken for the ‘North star’ at this time of year.
The real pole star, Polaris, is much less brilliant and is located higher in the north, 54 degrees above the horizon to be exact. Use the pointer stars in the Ploughs bowl to track it down.
Opposite the Plough and pole star, over in the northeast, the distinctive ‘W’ constellation of Queen Cassiopeia is conspicuous, whilst climbing off the NE horizon the hero Perseus, his love, Princess Andromeda and their ‘steed’ Pegasus will in a month’s time start to dominate the whole eastern aspect. Before then however Perseus will be the focus of attention for the annual Perseid meteor shower, more on this next time.
The Whitby and District Astronomical society will be hosting public Star Parties on Friday 19 and Saturday 20 July from the Captain Cook’s monument on the West Cliff, from 9.30pm.