|Winter: Orion Canis Major Canis Minor Monoceros Lepus Eridanus Taurus Auriga Camelopardalis Lynx Gemini Cancer|
|Spring: Hydra Sextans Crater Corvus Leo Leo Minor Ursa Major Ursa Minor Canes Venatici Coma Berenices Virgo Bootes|
|Summer: Draco Corona Borealis Hercules Ophiuchus Serpens Libra Scorpius Sagittarius Scutum Aquila Sagitta Vulpecula Lyra Cygnus|
|Autumn: Andromeda Perseus Pegasus Cassiopeia Cepheus Cetus Lacerta Delphinus Equuleus Capricornus Aquarius Pisces Aries|
|Southern Skies: Centaurus Crux Lupus Corona Australis Piscis Australis Sculptor Tucana Fornax Dorado Columba Puppis Carina Vela|
After the Big Dipper, the most recognizable grouping of stars in the northern sky is the big "W" of Cassiopeia. Nestled securely in the heart of the Milky Way, Cassiopeia is the queen who started a lot of trouble by boasting about her daughter Andromeda's beauty, which you can read all about in the Andromeda Story. The queen is usually depicted sitting on a throne, and to early Arabs, she was the lady in the chair.
The alpha star in the constellation is named Shedir, from the Arabic for breast. It is spectral class K0, magnitude 2.24, 230 light years away. The beta star is Caph, from the Arabic for palm. It is an F2 type star, magnitude 2.28, 55 light years away. The third named star in Cassiopeia is Ruchbah, from the Arabic for knee. Spectral type A5, the star has a magnitude of 2.68, and is 100 light years away.
Like most queens, Cassiopeia is surrounded by jewels. In this case the jewels are some of the myriad star clusters and nebulae that fill the middle of the Milky Way, where she sits on her throne. On her left hand, like a sparkling setting of diamonds, is the open star cluster M103, and on her right, the colorful star cluster M52.
Supernovae are the most powerful explosions in the universe, and they are very rare. They are caused by the death of a supermassive star, or more rarely by the collision of two stars. The light from a supernova explosion is brighter than the combined light of an entire galaxy full of hundreds of billions of stars, and can be seen across the universe from millions of light years away. But the light only lasts for a few weeks or months before fading away, leaving behind an immense cloud of expanding gas called a nebula, or supernova remnant, which can last for millions of years.
Observations of these remnants suggests that supernovae occur inside our own Milky Way galaxy about once every fifty years, and in all of recorded history there have been only five officially observed and recorded supernovae inside our galaxy. The first was SN 185, discovered in China in 185 AD. in the southern constellation of Circinus. The second was SN 1006, observed in the constellation Lupus, in 1006 AD. The third was SN 1054, observed in the constellation of Taurus, in 1054 AD, which gave rise to Messier's first catalogued "nebula", M1, otherwise known as the Crab Nebula (NGC 1952). Before the fifth and last supernova, SN 1604 (also known as Kepler's Star), was observed in the constellation Ophiuchus in 1604, Milky Way supernova number four SN 1572, occurred right here in the constellation of Cassiopeia, in 1572. The famous astronomer, Tycho Brahe, describes his discovery of the "new" star:
"On the 11th day of November in the evening after sunset, I was contemplating the stars in a clear sky. I noticed that a new and unusual star, surpassing the other stars in brilliancy, was shining almost directly above my head; and since I had, from boyhood, known all the stars of the heavens perfectly, it was quite evident to me that there had never been any star in that place of the sky, even the smallest, to say nothing of a star so conspicuous and bright as this. I was so astonished of this sight that I was not ashamed to doubt the trustworthiness of my own eyes. But when I observed that others, on having the place pointed out to them, could see that there was really a star there, I had no further doubts. A miracle indeed, one that has never been previously seen before our time, in any age since the beginning of the world."
Tycho initiated an in-depth study of the star, before the days of telescopes, publishing his results in his famous De Nova Stella, which included his hand drawn map of the star's position, and resulted in the star being given his name: Tycho's Star. A supernova explosion cannot be predicted, and the serendipity of Tycho's discovery means anyone familiar with the night sky could chance upon a similar sight, and possibly have their name immortalized in the star charts.
It would take another 400 years after Tycho's sighting before modern telescopes were able to detect the gaseous remnant of the SN 1572 explosion. The photo below is a x-ray infrared composite of the expanding gas cloud caused by the explosion. It is about 10,000 light years away, and expanding at a speed of about 20 million miles per hour.
Cassiopeia also contains the youngest supernova remnant so far discovered in our galaxy. Named Cassiopeia A, it is estimated to be 340 years old, but there is no record of anyone observing the supernova explosion that caused it. It is possible the initial material shed from the dying star obscured the final explosion.
NGC 7635, also known as The Bubble Nebula, is not a supernova remnant. The shell or bubble of expanding gas is not caused by a dying star, but from a freshly formed star. Embedded in a vast cloud of star formation known as an emission nebula, the stellar wind from this very large, very hot young star has created a bubble of gas around it that is expanding at four million miles per hour.
Another nebula not caused by a supernova is the Heart and Soul Nebula. Like the Orion Nebula, M42, it is a vast cloud of gas and dust where stars are being born. Below left is the Soul Nebula, IC 1848, also known as the Embryo Nebula, and W5. Below right is IC 1808, the Heart Nebula.
There have been two planetary systems discovered so far in the constellation Cassiopeia. Both of the stars are beyond naked eye visibility, and the planets are all gas giants. For the latest information on exoplanets, visit NASA's Planet Quest.