The Night Sky
March / April
With Spring not far away, Orion is setting earlier and earlier in the west – so have a last look at the Orion Nebula, it will be next Winter before you see it again. The stand-out constellation for Spring and early Summer is Leo and, unlike many constellations whose component stars have moved relative to each other over the last two thousand years or so, this is a constellation that has retained its namesake shape of a Sphinx-like recumbent lion. It is very recognisable and quite easy to find -
Just as you would use the ‘pointers’ of the Plough to find the North star, go in the opposite direction about the same distance – and there’s Leo waiting for you in the South East. The ‘Sickle’ asterism of the head and mane is particularly noticeable. Another useful piece of navigation in this part of the sky is to follow the arc of the handle of the Plough to Arcturus and then onwards to Spica in Virgo. Arc to Arcturus and spike to Spica, as the saying goes.
While Leo contains some nice double stars (Regulus and Algieba, in particular, are very fine doubles), the constellation is much better known for its galaxies.
M66 is a spiral galaxy that is part of the Leo Triplet, the other two members are M65 and NGC 3628. It is at a distance of 37 million light-years and has a somewhat distorted shape due to gravitational interactions with the other members of the Triplet, which are pulling stars away from M66. Eventually, the outermost stars may form a dwarf galaxy orbiting M66. Both M65 and M66 are visible in large binoculars or small telescopes, but their concentrated nuclei and elongation are only visible in larger telescopes.
M95 and M96 are both spiral galaxies 20 million light-years from Earth. Though they are visible as fuzzy objects in small telescopes, their structure is only visible in larger instruments. M95 is a barred spiral galaxy. M105 is about a degree away from the M95/M96 pair; it is an elliptical galaxy of the 9th magnitude, also about 20 million light-years from Earth.
NGC 2903 is a barred spiral galaxy discovered by William Herschel in 1784. It is very similar in size and shape to the Milky Way and is located 25 million light-years from Earth. In its core, NGC 2903 has many "hotspots", which have been found to be near regions of star formation - thought to be due to the presence of the dusty bar, which sends shock waves through its rotation to an area with a diameter of 2,000 light-years. The outskirts of the galaxy have many young open star clusters.
Best Double Stars this Spring:
There are some very pretty double stars in the constellation of Cancer which are well placed for springtime viewing:
Tegmine (ζ zeta Cancri) is a nice triple that requires a 6-inch scope and steady seeing to resolve the close components.
Ψ2 (Phi2) Cancri s another pretty twin system, located east of Pollux.
i (iota) Cancri is a springtime “Albireo,” with striking gold and blue colours.
Regulus α (alpha) Leonis presents a widely separated pair of stars that share a common proper motion.
Algeiba γ (gamma) Leonis is a beautiful slow-moving binary; both golden yellow.
Winnecke 4 (also known as Messier 40 or WNC 4) is a double star in the constellation Ursa Major – and while it is not a particularly notable double, it does have curiosity value:
It was discovered by Charles Messier in 1764 while he was searching for a nebula that had been reported in the area by Johannes Hevelius. Not seeing any nebulae, Messier catalogued this double star instead – for reasons best known to himself! It was subsequently rediscovered by Friedrich August Theodor Winnecke in 1863, and included in the Winnecke catalogue of double stars as number 4. Burnham calls M40 "one of the few real mistakes in the Messier catalogue," faulting Messier for including it when all he saw was a double star, not a nebula of any sort.
Cor Caroli α (alpha) Canum Venaticorum is one of the finest double stars in the sky for small telescopes – the colours have been described as white and slightly yellowish.
Mizar and Alcor are two stars forming a naked eye double in the handle of the Plough asterism in the constellation of Ursa Major. Mizar is the second star from the end of the Big Dipper's handle, and Alcor its faint companion. Mizar, also designated Zeta Ursae Majoris (ζ Ursae Majoris), is itself a quadruple system and Alcor, also designated 80 Ursae Majoris (80 UMa), is a binary, the pair together forming a sextuple system. The whole system lies about 83 light-years away from the Sun, as measured by the Hipparcos astrometry satellite.
(You will probably need Stellarium to locate these stars).
M-97 (The Owl Nebula) in Ursa Major is the only large planetary nebula viewable in the Spring skies. This large planetary nebula is almost 3' in diameter and appears as a gray puff of light, slightly brighter in the centre. At times, especially with averted vision, the "eyes" of the owl can be seen as two slightly darker spots.
M-51 (The Whirlpool Galaxy) is probably the finest example of a face-on spiral galaxy in the northern hemisphere, with a bright centre and rather easily seen spiral arms. Just a few arc-minutes to the north-east is its companion galaxy, NGC 5195. This object is small, with a brighter centre, and seemingly connected to M-51 by a bridge of stars.
M-3 is a pretty globular cluster in Canes Venatici and easier to find starting in Bootes. It is worth the trouble, since it is almost as spectacular as M13 in Hercules. M3 is the only major globular cluster in the spring sky and handles magnification well. There are many stars arranged in curving chains resolved at its edges.
The next meteor shower is the Lyrids, which is expected to peak on April 22 / 23. The Lyrids are created by debris from comet Thatcher, which takes about 415 years to orbit the Sun.