Archive for the ‘Constellations’ Category

Orion star hop!

Posted: February 11, 2012 in Constellations, Deepsky, NB75, Observing
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The bright star pattern of Orion is a great place to begin navigating the sky at this time of the year.  Orion is easy enough to find; face south and look for three bright stars a straight line.  Those stars mark Orion’s Belt and is the centre of the constellation.

If you can find the stars of Orion then you can use the shape to find other interesting stuff in the sky.  For example, you can hop from the three Belt stars to a few other things.

Follow the line from the stars down towards the horizon and you spot the brilliantly twinkling star called Sirius.  This is actually the brightest star in the sky (and one the nearest to us).  Sirius is a bit more massive than the Sun and this translates to it putting out more that 25 times as much energy as the Sun does. It is only outshone in the night sky by the planets Venus, Jupiter and occasionally Mars.  From the UK it never gets particularly high in the sky and so its light has to pass through the atmosphere at a shallow angle.  This causes it to twinkle violently and flash different colours of the rainbow.  This can make for some interesting pictures!

Following the Belt stars upwards will bring you to a bright orange star called Aldebaran which seems to be part of a V-formation of fainter stars around it.   Aldebaran is an old orang giant star about 65 light years away.  It’s the kind of bloated star that our Sun will evolve into when the nuclear fuel runs out in five or six billion years time.  Although Aldebaran seems to be embedded in the faint scattering of stars around it – this is an illusion.  The Hyades star cluster is more than twice as distant as Aldebaran.  This means we are closer to Aldebaran than it is to the stars that seem to be next to it in the sky!  Binoculars give a great view of Aldebaran and the Hyades cluster.

Continue that line from Orion up a bit further up in the same direction and you’ll arrive at the Pleaides star cluster (also called The Seven Sisters on account of how keen sighted people claim to be able to see seven stars….I can count five).  Astronomers give it the somewhat less romantic name M45.  The Pleaides are even more remote than the Hyades – about three times further away.  Here’s a picture Malcolm Robinson took of the cluster a couple of years ago:

The purpose of learning to hop from star to star is to help build up your familiarity with the night sky.  And it’s also useful for tracking down really faint fuzzy objects like nebulas and star clusters.  Here’s a nice example for those of you with binoculars or telescopes using what you’re seen so far.  There’s an nice little cluster of stars, called M41, in the constellation Canis Major (the Great Dog).  It’s near the star Sirius so we’ll use that to hop to M41.

So find Sirius, with binoculars or telescope and move down and slightly to the right.  M41 should jump out in your field of view with binoculars.  Look for those fainter stars to the south of Sirius to help you if you need it.

Here’s a simulated view of the cluster at low magnification (about 40x):

M41 is on the fringe of naked eye visibility.  Although it is best seen with a telescope there are suggestions it was seen by Aristotle in the 4th century BC.  It’s a scattering of about a hundred stars covering an area bigger than the full moon.  Many telescopic observers report seeing long chains of stars radiating away from the centre of cluster where a brighter orange giant star is found.  M41 is a typical example of the star clusters found throughout the Milky Way arching across the winter sky from northern to southern horizon.

More soon…

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In Northumberland on late on autumn evenings there’s a lonely star near the southern horizon.  It often goes unnoticed – perhaps hidden by nearby (or even distant) buildings or trees.  The name of the star is Fomalhaut (pronounced “fum-al-hort”).

Looking south during mid-October 2011 at 10.30pm.

Fomalhaut is a tough star to see from these northerly latitudes.  You can find it using the popular “Square of Pegasus” stars shown above.  Follow a line from the two right-hand stars down to the horizon.  It’s typically only visible for just a few hours each night and it climbs just 6 degrees above the southern horizon at most.  The further north you are, the harder it gets!  Way up past 61 degrees north it doesn’t rise at all.

Fomalhaut is a 1st magnitude star and compared with the stars of the Summer Triangle, it is brighter than Deneb but doesn’t quite rival Altair.  But Fomalhaut at its best is shining through 10 times as much air as a star overhead.  It’s light is scattered and the star is dimmed significantly.  If the air is unsteady it can twinkle like few other stars in the sky can!

Here’s a picture Fomalhaut at visible and near infrared wavelengths:

Fomalhaut - the brightest star in Piscis Austrinus.

I had great fun assembling this image from individual infrared, red and blue images lifted from the STScI Digitized Sky Survey website!

Fomalhaut is a white, main sequence star just 25 light years away.  It’s the brightest star in the constellation Piscis Austrinus (the Southern Fish).  Astronomers have found that Fomalhaut is a shade over twice the Sun’s mass and it puts out 18 times more light than the Sun does.  Interestingly the motion of Fomalhaut through space suggests that it shares a birth place with several other bright stars in the sky – the so called Castor Moving Group.  So Fomalhaut formed from the same nebula as Castor (in Gemini), Vega (in Lyra) and Zubenelgenubi (in Libra) along with others.  These stars are widely scattered across the sky today but their common motion puts them at the same location in space sometime in the last 300 million years!

Fomalhaut is well known to astronomers because it is surrounded by a warm, dusty disk of material resembling the Kuiper Belt in our solar system.  In recent years the HST has actually directly imaged a planet orbiting within the disk – the planet is named Fomalhaut b.

Fomalhaut b is trillions of times fainter than its parent star – it’s only visible in the HST picture because the star is mostly blocked out and some delicate image processing has been applied after that (the white circle shows the location of the star).  The mass of the planet is not know with certainty but may be half as massive, to twice as massive as Jupiter.  It’s at a great distance from Fomalhaut – about 115AUs, which is nearly four times the distance of Neptune from the Sun.  It will take Fomalhaut b about 870 years to go around its star.

So Fomalhaut is not actually as lonely as it appears in our skies!

Winter Stars

Posted: January 5, 2011 in Constellations, Deepsky
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First attempt at astro imaging with the Nikon D80.  Opened the shutter for 30 seconds to get Orion, Canis Minor and Canis Major.  Very light polluted just outside our back door in Morpeth!  Taken at 11pm.