12 Dec 2010

(Please click images to enlarge)

Constellation of the Month: Cassiopeia

(vote in the sidebar which will be the next Constellation of the Month!)

Last month we looked at the constellation of the Plough. I hope everyone managed to get a glimpse through the snow clouds and find it. Maybe you even had the chance to name the stars (and show off a little to your friends you know something about it! :-) )

This month, I was going to do Ursa Major's smaller bear friend, Ursa Minor (which means 'Small Bear'). However, it was pointed out to me that a constellation that is very clear in the sky just now is Cassiopeia, and this would be better to learn next, because it will help guide you through the sky easier...you'll soon see why!



What does it look like?

Let's start off by finding out what this asterism (remember, asterism means pattern of stars?) looks like. Easy! It's shaped like a huge W


(although, because it swings around the North star as the Earth turns (i.e. it is circumpolar), sometimes it will look like it's fallen on its side, and sometimes it will look like an M

Trying to understand where the W shape comes from, I have looked at a lot of images on the Internet. I haven't found most of them very helpful (I can see the stars, but can't make them into the W shape). These are a few of the images of Cassiopeia I found [click on image to see better]:

After some searching, I found an old one I liked, that I could understand where in Casseopia's body the (five) main stars are, which I've marked with yellow dots. The W is on it's side (looking more like a 3):



This one is also clear (and appears to be as described by the ancient greeks):




The Main Stars


So, now it's time to name the main stars (there are more, but we'll leave that for a bit): Caph, Shedar (also called α Cas, α Cassiopeiae, Shedar, Shadar, Schedir, or Shedir), Tsi (Gamma Cassiopeia), Ruchbah (Delta Cas) and Segin (Epsilon Cas):


And see what it looks like with a few other stars surrounding it. (Try squinting...that sometimes helps):

Can't see the stars? (Truth be told, neither can I in photos, though I can see them clearly outside :-) ) Take a look at the left image below. It's exactly the same as the one above, but with the stars of the constellation highlighted with yellow dots; and in the right image the constellation lines are back, so you can compare with the image above (Really, it's easier to see them in the sky!)


Ok, so now we know what Cassiopeia looks like, we need to know where to find it. If we can find the Plough, we can find Cassiopeia:






Where is it?
Cassiopeia and the Plough are on opposite sides of the North star (Polaris) to each other, both rotating around it.



This means that, if the Plough is low on the horizon below the North Star, then Cassiopeia will be high in the sky above the North Star and more easily visible, and vice versa. When The Plough is high, Cassiopeia is low on the horizon. As they rotate around there will be times when both will be about level with each other and the North Star, and all three will be clear.




So, when you can't see the Plough, Cassiopeia can be used to locate the North Star (Polaris):





This is the reason I decided to do Cassiopeia before Ursa Minor - because, if you can find both the Plough and Cassiopeia, it will make finding Ursa Minor much easier, since it's tucked nicely between the two!




It's all Greek to me!

Before I go into what objects and interesting things can be found in Cassiopeia, I'm just going to flash this table at you.
Lots of star names are made from combining a greek letter and the constellation name. The nearer to the beginning of the alphabet the letter, the more likely it is that it's a brighter star eg Alpha = brightest, Beta = next brightest and so on....
So, a very quick look at the alphabet, will give you a clue to how 'important'/ prominent is a star within the constellation.
(I'll put this up in the sidebar for future reference.)









Interesting Objects in Cassiopeia




An object map (from Derekscope) shows where some of the following objects are located [as usual, click to see clearer]:




Heart and Soul Nebulae

Cassiopeia seems to be a very active constellation... To start with, there's the wonderfully named Heart and Soul Nebulas (guess which one's the heart!):


...which can be found here:


Here's an image of the Soul Nebula, containing the the radio source, W5 , a massive star-forming region within the nebula (6500 light years away) (infrared):


This is the famous 'Mountains of Creation', within the soul nebula, where stars are born:




...and this one shows how a super massive sun in W5 is blowing off the dust discs from smaller suns, both images taken by the Spitzer Space Telescope:





It's windy in Cassiopeia! Image credit:
NASA/JPL-Caltech/Harvard-Smithsonian CfA




Rho Cassiopeia
And talking of active, there are only seven known yellow hypergiants in the Milky Way, and two of them are in Cassiopeia. The first is called Rho Cassiopeia. It is about 11,650 light-years away from Earth and yet, amazingly, it can be seen with the naked eye. It's about 550,000 times the brightness (luminosity) of our sun! You can find it just here near the end of the W:



This particular star gets brighter and dimmer (it's a variable star) as it throws off its outer layer about every 50 years, and may be close to going supernova (In fact, some scientists think it may have already gone supernova, and may now be a black hole or a neutron star, but that we're just too far away to have seen it yet!)





The other yellow hypergiant in Cassiopeia is called V509 Cassiopeia (V509 Cas), which is also a variable star, though smaller than Rho Cas.




Cassiopeia A (Cas A)



Whilst Rho Cas might have gone supernova, there are two stars in Cassiopeia that have definately exploded. The first was in 1572, which became brighter than Venus in the sky, and the second is called (unimaginatively) Cassiopeia A (or Cas A). This is the most recent (about 1667) supernova in our own Milky Way, and is the 'brightest' radio source in the sky:






The blown off gas and dust (the remnant) can be faintly seen:



(It's thought that the neutron star in the middle
might actually have a carbon atmosphere)

Although there are many, many images in a google search for Cas A, I had great difficulty finding out where it was actually located!In the end, I estimated its position using Stellarium:








Shedir

Apart from being a hotbed of supernova and star forming activity, Cassiopeia has another claim to fame - it's absolutely, super massive, amazingly big Alpha star, Shedir! If you look at this image, you can see how small it makes our sun (which is actually a pretty average sized sun) look:



[Our sun's in the top right corner]



Though it's so big, and although it is the Alpha star in Cassiopeia, it's not the brightest star of the constellation. That claim to fame goes to Rho Cas (above).


Achird

There is a binary star (two stars linked by gravity to each other) in Cassiopeia, which can be found quite close to the second 'V' dip of the W, called Achird:

As for the Plough, I'll leave you with an idea of the distances of the stars in the constellation. I managed to find two source for this. The first is from Warren-Wilson:



and the second takes a 3D look at the stars:






(We're looking up from the bottom right corner)


There is so much more information I've collected for this constellation, for instance:



but, if I were to put everything there was about this constellation here, I would be writing this for a long time to come. So, I hope there is enough here to get you going and explore this constellation yourself!




'Constellation of the Month' now moved to new website:

9 Comments:

Anonymous Anonymous said...

Really is quite interesting. I never understood before how the "W" made a person, and now I know :)

12 December 2010 at 17:52  
Blogger Unknown said...

Thanks for your feedback anonymous.

I must admit, some of the constellations vary from one source to another. Looking at the two images I picked out for Cassiopeia, for example, the stars are on different parts of the body. According to the naming, the second image is the most accurate, but other images have become accepted.

I don't know if the information here is too much/ too little? If anyone has a thought about this, please leave a comment. Thanks

12 December 2010 at 18:24  
Blogger Savage said...

Years ago at Winter Camp (north woods, bitterly cold, but amazingly clear skies), our instructor taught us to find Cassiopeia by having us think of the shape as neither a 'W' nor her body, but rather as her *throne*. (Turn the image in a certain direction, and it'll take on roughly the shape of a chair, with a tall back, a seat and a footrest.)

As the mythology went, Cassiopeia had ordered her daughter Andromeda chained to a rock. In response to this, Cassiopeia was ordered to sit in this 'sky throne,' where as a punishment she would spend half of every night in her throne upside down.

And as your diagram shows, with Cassiopeia circling around Polaris nightly, she does indeed spend half the night upside down.

No idea where that instructor got this story. But it's worked for me... after hearing it, I'd always found Cassiopeia east to spot.

Enjoying the column... keep 'em coming! tws

13 December 2010 at 02:31  
Blogger Bluezy said...

Lots of great info! I have a question. I never really worried about direction as long as I knew where the north star was. I DID not know that about Cassiopea.
But now I am looking at a chart and the star chart reads east is to the left. It is not like a map. I guess that is why it is not called a sky map, but a chart. I get that when things move you can chart it. Ok -My kids are trying to tell me they have a compass and that I am all backwards, but I have done the dipper thing so many times last summer that I know where north is.

13 December 2010 at 04:09  
Blogger Bluezy said...

later I find out that my daughter was messing with me and thought it was funny how I debated NO NO I have seen the north star a million times..

KIDS lol

I also found planisphere on the web. I never really really remember the east on the right side of the paper.

14 December 2010 at 14:08  
Blogger Unknown said...

Hi Savage, I love the idea of Winter Camp...I've never heard of that before!

Try as I might, I can only see the W!! (or M, as the timing may be...) I can't see the throne :-(

It's a great story (and made a great film :-)) And I like the way it joins Cassiopeia with the others in the story:
Cepheus (her husband, the king),
Andromeda (her daughter),
Perseus (her daughter's rescuer)and
Pegasus (his flying horse)as well as
Cetus (the monster attacking Andromeda)
- all other constellations nearby in the sky!! [hopefully I'll get around to covering those constellations eventually :-D ]

Hey there Bluezy.
Lol...your kids ribbing you about knowing where North is. I'm sure, if you've worked out the North Star from the Dipper, you're right :-) I'm sure you've also noticed the sun rising in the East and setting in the West, which will confirm how right you are!

To get a feel for how the sky looks, I'd really recommend a program we use in the school called Stellarium, which can be set to your location. Then you can put in the time (put an after dark hour) and date, and see what you should see in the sky. Using that, you can locate different constallations and objects before you go out (besides which, it's great fun to play with! :-D ) (if you decide to download it, let me know if you have any problems using it...I can always do a post to explain it best I can...)

I've been trying to work out what your question was? lol

14 December 2010 at 19:57  
Anonymous Anonymous said...

Cassiopeia had a horible end in the Clash of the Titans movie (the new one)!

21 December 2010 at 19:16  
Anonymous Ophiuchus said...

Love that film! I think she deserved it :-)

22 December 2010 at 14:36  
Anonymous Anonymous said...

thanks for this site its exactly what ive been looking for how can i find an image of cas in 3d?im interested in knowing the distance the stars are in depth as well as width?

3 August 2012 at 13:58  

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