Another clear night was forecast so I was set with my targets: a couple of hours each on M104 (the Sombrero Galaxy) and M64 (the Black Eye Galaxy). In the end, there were clear spells and lots of cloud. Rather than a couple of hours I got half an hour on each object!
These were taken with my usual setup: Nikon D90 at prime focus of the 8 inch (200mm) Meade LX10. ISO800 with 4 minute subs. Images stacked in Deepsky Stacker and tweaked in Photoshop.
Both galaxies have prominent dust lanes.
Before packing up I noticed Cygnus was pretty high in the eastern sky so I grabbed some subs of Albireo, the famous double star.
Albireo is a fantastic sight through any telescope: a bright golden primary with a fainter bluish secondary separated by around 35 arcseconds. The above picture was taken on the same setup as the earlier galaxy pictures. I decided to expose for a rich starfield which meant overexposing Albireo. The colour still present well so I'm happy with the image!
I was mostly facing south while taking my pictures. At around 1am I glanced towards the north and saw faint rays of light reaching 20 or 30 degrees above the horizon: an unexpected aurora! I went for my other camera and tripod but the activity had died down substantially. I took a 30 second exposure at ISO1600 and this is what I got:
The colours were not particularly visible to the eye; the overall impression was that the sky was bright in the north. Got to bed (after image processing!) at around 4am.
Last night provided a brief window of opportunity between the end of (nautical) twilight and moonrise to get some images. It was going to have to be bright target because of the time limit. In the end I chose the globular cluster M5 in the constellation Serpens.
M5 is one of the brighter globular clusters in the sky. The apparent magnitude is given as +5.7 which makes it a naked eye object from exceptionally dark skies. The angular size is around 20 arcminutes - around 2/3 of the apparent diameter of the full moon. I suspect it's often overlooked by my astronomical friends in favour of M13 (the Hercules Globular) which is a shade brighter, larger and higher in the sky.
M5 is thought to be around 24,000 light-years away. The number of stars in the cluster runs into the low hundreds of thousands. It is physically one of the larger Milky Way globular clusters with an estimated diameter of around 150 light-years.
It doesn't get dark enough to take pictures like this now until after 11pm. When will the next clear sky come? I've already chosen my next target!
This is a whole sky chart for the May night sky. The seven stars of The Plough (part of Ursa Major) are overhead. Follow the tail stars (Alioth, Mizar, Alkaid) and arc down to Arcturus, the leading star of Bootes (the Herdsman) and the brightest star above the horizon at this time. Arcturus is an evolved orange giant star and a bit of an interloper in the neighbourhood. It is around 37 light-years away but plunging through the disk of the Milky Way along a trajectory which brought it in from the halo surrounding our Galaxy.
Keep following the curve through Arcturus and you'll arrive at Spica, a bright white star nearly half way up the sky above the southern horizon. Spica is the brightest star in Virgo, the Maiden. Spica appears as a single star to the eye and even through large telescopes. However, spectroscopic analysis of the light from Spica reveals it to consist of a pair of stars - each slightly heavier than the Sun - in close orbit around each other with a period of 4 days. The average distance between the pair is just 2 million km!
The star Porrima is also a notable binary star. It consists of two stars slightly heavier and more luminous than our Sun orbiting each other with a period of 168 years. They were at their closest together in 2011 at which point only large observatory telescopes could resolve the two stars. In 2018 I’ve been able to split the two stars with my modest 8-inch telescope. They will continue to separate for the rest of my life!
Beyond the stars of Virgo and beyond the Milky Way is the Virgo Cluster of galaxies. You can see the brightest members with their Messier designations on the chart above. The centre of the Virgo Cluster lies around 50 million light-years away. There are about 1500 – 2000 galaxies in the cluster. The Virgo Cluster is heart of a much larger structure – the Virgo Super Cluster and our Milky Way is an outlying member of that! The Milky Way, the Andromeda Galaxy and a few dozen others in the neighbourhood are being drawn across the universe by the invisible gravitational pull of these distant Spring-time galaxies.
Over in the west the last of the traditional winter constellations are sinking below the horizon. Gemini, with the twin bright stars Castor and Pollux, can be seen for a short period after dusk. Venus is traversing Gemini this month. Cancer (the Crab) and Leo (the Lion) are a little higher. The Beehive cluster (M 44) in Cancer and the Leo Triplet of galaxies (whose brightest members are M 65 and M 66) can still be found with binoculars and telescopes respectively.
In the east the Milky Way and summer constellations are beginning to rise. Vega, Deneb and Altair - bright stars which form an asterism called The Summer Triangle - mark the most prominent section of the Milky Way. With each successive evening the Milky Way climbs higher in the sky a little earlier. Unfortunately, a period of all night twilight is beginning for the northern UK and the nights are getting shorter and lighter. Better opportunities to see the Milky Way will come in August and September.
Venus is visible for a couple of hours after sunset where it blazes brilliantly above the north west horizon. Keen sighted observers can actually spot it before the sun goes down! The planet is still on the far side of its orbit and telescopes reveal a very small disk (around 12-13 arcseconds) with a distinctly gibbous phase. Don't expect to see to any detail on Venus! The atmosphere is highly reflective and contrast can usually only be seen with UV filters.
The planet Jupiter comes to opposition on May 9th and is visible from sunset until sunrise. The best time to view Jupiter is when it is highest in the sky - around local midnight (1am BST). At opposition a planet is at its nearest to Earth for the year and appears larger through a telescope than at other times of the year. Jupiter is about 658 million km away (4.4 times the Earth-Sun distance) and the Jovian disk measures 45 arcseconds across its equator. Binoculars and small telescopes easily reveal the four largest moons (Io, Europa, Ganymede and Callisto) as they change position from night to night. Larger telescopes show the equatorial bands (looking rather like a pair of stripes parallel to the equator) which are clouds whipped by fast moving jet streams in Jupiter's atmosphere. Unfortunately, Jupiter is in the southern constellation Libra and is never more than about 20 degrees above the horizon (from Northumberland). At low elevation we view the planet through much more of the atmosphere and we need a very steady atmosphere indeed to see more detail in the clouds. The situation will begin to improve in around 5-6 years when Jupiter begins to head back into northern skies...
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Dr Adrian Jannetta. Amateur astronomer, maths teacher and science enthusiast.