April Night Sky
Jupiter remains the brightest planet in the night sky high up in Gemini and is a rewarding target for any telescope during April, however in terms of observing ‘focus’ Mars may take top billing this month. The red planet reaches opposition on April 8th when for the first time in almost two years Mars will once again be closest in its orbit to Earth and will be visible all night. Throughout the evening look for a conspicuous ‘orange’ star over in the SE and to the left of Spica – a bright white star in Virgo. Closest oppositions occur in a 15–17 year cycle, but even these vary in distance, for instance in 2003 Mars came within 34.5 million miles of Earth, the closest for some 60,000 years. By 2010 Mars was over 62 million miles distant at opposition. There is a slight improvement this time round, but as Mars is quite a small world, little more than half Earth’s diameter, its disk is never very large when viewed through a telescope, even at a close opposition. Still, under steady seeing conditions Mars does show some surface detail, in particular the polar cap and some darker surface markings. The Moon lies below Mars on the 14th. One final cautionary note, should you come across an article on the Internet or via email reporting that Mars will be the size of the full Moon – please ignore and bin it!
Saturn is now rising just before midnight, but is best observed through a telescope in the early morning hours when it is higher in the sky and clear of any turbulent air. By dawn Saturn lies over in the SW. Venus is seen as a brilliant object low down in the same direction an hour before sunrise. The moon lies near Saturn on the 17th and Venus on the 25th.
The Spring Sky
Compared to the departing stellar canopy of winter, at first glance the spring sky may seem rather less inspiring. Yet appearances can be deceptive and there is much to wonder at amongst the constellations now arranged across the south and east. Our tour commences as darkness falls, around 9.45 pm. By then Leo, the most readily identifiable spring constellation, is located due south. The head and mane of the lion is marked by the distinctive star asterism known as the ‘sickle’, although some people view it as a backwards question mark. At the base of this arrangement shines prominent Regulus, Leo’s chief star, and faintest of the first magnitude stars.
To the left of the sickle, a ‘triangle’ of stars depicts the hindquarters of Leo. Just beneath an imaginary line joining Regulus to Denebola, the rearmost star of this triangle, a number of galaxies are found, some of which are visible under good seeing conditions in smaller scopes. Ahead of Leo scuttles Cancer, faintest of the zodiac constellations the stars which are often drowned out by moonlight or light pollution. Cancer is home to the fine open cluster M44 or Beehive, sometimes known as the Praesepe; ‘the ‘manger’. To the naked eye it appears as a misty patch, but a small scope reveals many individual stars.
Our next destination, Hydra – Water Serpent – is the largest constellation in the heavens, extending from below Cancer in the WSW, to beneath Virgo down in the ESE. Indeed it is well after 11 pm before the entire constellation is visible. Hydra’s brightest star; Alphard – the ‘solitary one’ – is located a hand’s span to the southeast of the distinctive, though rather faint, loop of stars marking the beast’s writhing heads, visible to the right of Regulus. Towards the tail of Hydra, two small but original constellations rest on the snake’s body: Corvus the Crow and Crater the Cup. The outline of Crater is rather faint and therefore difficult to trace in light-polluted skies. Corvus is more prominent – a quadrilateral grouping of stars that mariners and astronomers alike refer to as ‘Spica’s Spanker’ (a spanker being a type of sail) – nearby the bright star Spica in Virgo. This constellation is the second largest in the sky, the outline of which can be likened to that of a large distorted letter ‘y’ with Spica situated at the bottom of the ‘leg’.
The area of sky within the bowl of the ‘y’, extending up to our next port of call, Coma Berenices, is referred to by astronomers as the ‘realm of galaxies’. It is a ‘window’ on to the wider universe through which many galaxies belonging to our local super cluster are revealed in large backyard scopes. A couple of dozen of the brighter galaxies are seen in typical amateur scopes. The Virgo cluster lies over 48 million light years away; however the galaxies associated with the larger Coma cluster are almost ten times that distance. All of the galaxies appear as elliptical or elongated smudges. The constellation of Coma itself is just a smattering of stars, but is one of the original 48 star groups.
Our final destination, Bootes, pronounced Bo-eh-tes, is currently visible in the ESE. The outline of the constellation resembles that of long kite, dented somewhat on one side. Its chief star, brilliant Arcturus, resides at the foot of this pattern. The name Arcturus comes from the Greek meaning ‘guardian of the bear’ due to its relative proximity to the Great Bear. Arcturus is the second brightest star visible from Britain and has a lovely deep amber hue. At just 37 light years it is the nearest example of an orange giant star, being some 30 times greater in diameter than our Sun, rather cooler and much older. Of all the visible bright stars, Arcturus has the greatest ‘proper’ motion, the true movement of a star as seen against the background sky. Like a fighter-bomber diving from high above, Arcturus is plunging through the galactic plane, cutting across the path of our Sun’s trajectory as it orbits around the Milky Way. As a consequence Arcturus appears to move a distance in the sky equivalent to the moon’s diameter every 1,000 years. In just a few hundred years it will be at its brightest as viewed from Earth; thereafter it will rapidly diminish in brilliance, and in a few thousand years will become just another anonymous face in the stellar crowd.
by Mark Lawson, Whitby & District Astronomical SocietyFor more info visit www.whitby-astronomers.com