A double dip in the BIg Dipper

Ursa Major is one of the most recognizable constellations in the northern sky. The tail end of the constellation is called by our American cousins the Big Dipper because it looks just like a huge water ladle in the sky. This picture was taken with a Camedia C2040 without the use of a scope (I had to wait until 3 in the morning to take this picture as the bloody neighbours had all their bloody lights on all night until 3 and it was polluting my views). The star in the middle of the 'handle' is called and if you look really carefully (without telescopes or binoculars), you might even see two stars. That's because there is a second much fainter star called Alcor. The ability to resolve the two stars with the naked eye is often quoted as a test of eyesight - if you can't see two stars, you probably need glasses!

Okay, time to use the telescope now, with a Neximage CCD imager and magnification equivalent to a 6mm eyepiece. The two stars can be clearly seen now. They are about 1.1 light years apart (that's 6,500,000,000,000 miles!) but are what's called a true binary system - that is, they orbit around one another. But that's not at all. Mizar (on the right) may look like one star but it's actually two - Mizar A and Mizar B. Mizar A is closer in the foreground and shines so brightly that's its luminance blocks out Mizar B, which is slightly behind it. 

Let's take a closer look at Mizar. Stick on a 3X Barlow lens to the CCD imager and all is revealed - a binary star system within another binary star system. Mizar A is the larger star that we see in the foregound. Not only that - stereoscopic studies have shown that Mizar A actually has another companion star that, unfortunately, is too close to it to resolve with any earth-bound telescope.

Seeing double: The joys of binary stars

A binary star is a star system consisting of two (or more) stars orbiting around their common center of mass. We had cloudless skies over Longstanton for the first time this year, so I managed to have a quick look at a few binary star systems last January (despite the glare from the gibbous moon and bloody freezing cold).  The first is Cor Caroli, which can be found in the crook of the Big Dipper's handle, just to its right, standing almost due east. The star is a true binary, consisting of two stars orbit each other (each orbit is estimated to take about 7,900 years). These two stars are designated Alpha-1 (the fainter of the two) and Alpha-2, and are thought to be about 650 Astronomical Units apart (that's 650 times the distance between the Earth and the Sun).

And here's a processed still image of the video:

A close-up of Cor Carioli. Cor Carioli (the heart of Charles) is named after Charles I of England, who was executed during the English Civil War in 1649. According to legend, this star brightened when his son, Charles II, return from exile on May 29, 1660. Cor Carioli is in fact a variable (it's brightness changes). The strong magnetic field of these stars are believed to produce starspots of enormous extent, which cause their brightness to vary considerably during their rotation.

We now come to Polaris below, so named due to the position of the star near the north celestial pole. Point a telescope at any other star and you will see it moving across your field of view, but point it at Polaris and it stays dead still. This made it a reliable beacon for early navigators. Polaris actually consists of one bright star - Polaris A - and two companion stars. The brighter of the two companions, Polaris B (the faint star on the left of the picture), is about 2000 Astronomical Units (AU) away from Polaris A (that's 2000 times the distance between the Earth and the Sun). Polaris A actually has another close companion star orbiting with 5 AU from the primary but it is too close to the primary star to be resolved visually.

Not everything that looks like a double is in fact a binary star system. Procyon below IS a binary star system, consisting of a white main sequence star Procyon A, and a faint white dwarf companion Procyon B. However, that faint star to the left is NOT Procyon B. The separation of Procyon A and B is 15.0 AUs - a little less than the distance between Uranus and the Sun - so Procyon B would be too faint and too close to the 'glare' of Procyon B to be observable on an 80mm scope. At a distance of 11.46 light-years away from earth, Procyon is one of our near neighbours.

The Colour of Stars

You might think that the stars that we see in the night sky are all white but that is only because our eyes cannot easily distinguish colours when objects are very faint. In reality, the night skies are ablaze with colour, with stars ranging from cool blue hues to fiery reds. Take a look at the image of the constellation Orion below. In particular, look at the top left star Betelgeuse and the bottom right star Rigel. They might look white initially but even on a fast 2-second exposure without the aid of a telescope, closer inspection of the picture can reveal a glimpse of reds and blues.

Zoom in with a telescope and Betelgeuse can now clearly be seen below as a fiery red star. That's because Betelgeuse is classified as a Class M red supergiant, one of the largest stars known. Strange as this may seem, fiery red usually indicates a cool star that is losing its radiation and dying out, while cool blue stars are the hottest, youngest stars. Betelgeuse is in fact in the last stages of its life and is expected to go supernova any time in the next million years (which is a very short time in stellar terms).

You can go deeper into the mysteries of star colours with spectroscopy - this is the science of determining the properties of a star by analysing the electromagnetic light radiation from it. By attaching a special optical filter called the Star Analyser 100 to my telescope eyepiece, I am now able to see the the colour spectrum that is unique to light radiation produced by Betelgeuse. The Star Analyser is basically a diffraction grating (as you would see on the surface of a CD or DVD) that is mounted in a standard 1.25 inch optical filter cell.

The image of the spectrum produced by the Star Analyser can be further analsyed using special software to reveal the spectral profile of the star that will tell you a lot about the star you are observing. The broad shape of the spectrum gives information about temperature - for example, this spectrum of cool Betelgeuse is quite different to that of hot Sirius. Narrow absorption (dark) or emission(bright) lines on the spectrum tell us about the chemical elements that are present in the star and how they are behaving - for example the spectrum of Betelgeuse reveals the tell-tale signature of molecules (and not just hydrogen atoms) in its atmosphere. The software I used to produce this spectral profile is a free product called Visual Spec - see http://astrosurf.com/vdesnoux/

Now let's take a look at the star in the opposite end of Orion, Rigel. Seen through the telescope below, you can clearly see that this is a pale blue star. Rigel is in fact a Class B blue supergiant. While blue supergiants are much smaller than their red counterparts (like Betelgeuse), they are amongst the hottest and brightest stars in the known Universe.

 

Attach the Star Analyser to the front of the CCD imager eyepiece and you'll see the spectrum produced by Rigel is quite different from that of Betelgeuse - with the bands in the blue end of the spectrum much stronger and the red band being significantly weaker.

Analysis of this spectrum with Visual Spec shows a presence of neutral helium and moderate hydrogen lines. Ionized metal lines include Magnesium II and Silicon II.

Let's now take a look at Sirius - the Dog Star. Sirius is the brightest star in the night sky and that is primarily because of its intrinsic luminosity and its proximity to our Earth. At a distance of just 8.6 light years away, the Sirius system is one of Earth's near neighbors. It is a Class A star - amongst the more common naked eye stars - and these are white or bluish-white, as you can see from the image below.

The spectrum produced by Sirius:

Analysis of Sirius' spectral band reveals strong hydrogen lines and also lines of ionized metals (Iron II, Magnesium II, Silicon II) and the presence of Calcium II lines.

And I can't talk about the colour of stars without of course mentioning our very own star - the sun. The sun is sometimes called a yellow star and it does indeed appear yellow to us on Earth (viewed through our atmosphere) but the Sun's own intrinsic color is white (aside from sunspots), with no trace of color. And if you want to do a spectral analysis of the sun, there's no need for a Star Analyser 100 to produce an image of its spectrum bands - just look out for the rainbow in the sky just after it rains!

The Bull

A wide full-view shot of the constellation Taurus, with (clockwise) the Pleiades cluster, Hyades cluster (including its brightest star Aldebaran) Tau Tauri and Elnath. Taken in October 2011, with my Olympus Camedia 4040-Z piggy-backed on the telescope.

The distinct arrowhead-shape of the Hyades cluster below.

Orion the hunter (and a Close Encounter of the Third Kind .....)

Orion is one of the most conspicuous, and most recognizable, constellations in the winter night sky - with the bright red Betelgeuse in the top left corner, the three stars of Orion's 'belt', the Orion nebula just below it and Rigel, the constellation's brightest star, in the bottom right corner.

The fiery red star below, Betelgeuse, is classified as a Class M red supergiant, one of the largest stars known. Strange as this may seem, fiery red usually indicates a cool star that is losing its radiation and dying out, while cool blue stars are the hottest, youngest stars. Betelgeuse is in fact in the last stages of its life and is expected to go supernova any time in the next million years (which is a very short time in stellar terms).

By contrast, right at the opposite end of Orion, is a bright pale blue star, Rigel. Rigel is a Class B blue supergiant. While blue supergiants are much smaller than their red counterparts (like Betelgeuse), they are amongst the hottest and brightest stars in the known Universe.

The three stars in the 'belt' below are, from left to right, Alnitak, Alnilam and Mintaka. And right below the belt is Orion's 'sword', where the Orion Nebula is located.

And just minutes after I took the image above, a strange alien craft flashed past right out of where the Orion Nebula is located - you can see the light trail left by it in the right bottom corner of the image below. Though the regular pattern of red lights of the Unidentified Flying Object may indicate that it is probably not as unidentified as I thought - this is the tell-tale signature of the warning lights of a very Earth-bound aeroplane.

Charioteer of the skies

The constellation Auriga is dominated by the bright star Capella and looks like a distorted pentagon. The name Auriga is Latin for 'charioteer' - its stars form a shape that was thought to resemble the helmet of a charioteer. Photo taken on an Olympus Camedia 2040Z piggy-backed on the telescope.

Capella (Alpha Aurigae) below is the brightest star in Auriga and the third brightest star in the northern hemisphere, after Arcturus and Vega. Although it appears to be a single star visually, spectroscopic observations have revealed that it is actually a star system of four stars in two binary pairs Capella means "small goat" - Auriga is usually pictured as a charioteer wielding a whip in one hand and holding a goat (Capella) and her two kids in the other. Photo taken afocally using a 10mm eyepiece on the telescope.

Eta Aurigae and Zeta Aurigae below are the 'kids' of Capella's goat. Epsilon Aurigae at the top is an unusual eclipsing binary system - it brightens then dims every 700 days due to being obscured by a huge dark disk orbiting an unknown object. Photo below taken afocally using a 10mm eyepiece on the telescope.

Menkalinan (Beta Aurigae) below is actually a ternary (triple) star system, although the light that the star system releases forges the appearance of a single star in the night sky. The third star, Beta Aurigae C, is a red dwarf star that is invisible to the naked eye. Photo taken afocally using a 10mm eyepiece on the telescope.

The Seven Sisters

The Pleiades, or Seven Sisters are among the nearest star clusters to Earth and is the cluster most obvious to the naked eye in the night sky. These shot was taken by me on October 2011, just with my Olympus Camedia C4040-Z piggy-backed on the telescope - see, you don't even need a telescope do stargaze!

Pleiades as you would see it with the naked eye looking over the horizon 

Next time you're out looking up at the night sky, try and see how many stars in Pleiades you can actually count. While it's called the Seven Sisters, you'd probably be able to see only six stars. In Greek mythology, the missing 'Sister' is Merope and you can't see her because she has hid herself in shame because she was the only sister who married a mortal human and not a god.
 

The Pleiades in Japanese is 'Subaru' - and the car manufacturer's logo is inspired by this star cluster!