Saturday, January 25, 2014

Great Nebula in Carinae

Last December 31st at 3 am, local time, I had one last try of the year to catch another Messier Object. I set up my telescope and the sky was full of stars even more in the south. However, I went for M53, a globular cluster in Coma Berenices, which was in the Eastern part of the sky. Normally, no star in this constellation is visible with the naked eye because of LP in the city, but remarkably this night, the star αCom was just visible with averted vision.

It took some time to spot and sketch M53 so I finished at about 4:15. There was some extra time before I had to get ready for work so I gave a quick look at Berenice’s hair with the binoculars and it was really impressive to see all those bright stars in it. Subsequently, I looked to the south and there it was a fantastic view of the great nebula in Carina. Some time ago I had seen it through the 15x70 Binoculars, sketched it and after processing the sketch, at the left, I sent it in to ASOD (Astronomy Sketch Of the Day).

This time, I wanted to go for more. Through the telescope view, I could see the “nebula region” in the great Carina Nebula. It seemed sort of like the HII region I saw in Orion Nebula and Lagoon Nebula.
It was really fascinating and the best gift from the sky in 2013. Unfortunately, the time for getting ready for work came quickly so I decided to try again on a future night in January in 2014.

And the time to sketch finally came. The early morning of Saturday January 4th I was ready to spend all that time stargazing because I did not need to work during the day. I set up the telescope at about 1 in the morning and evaluated the sky: moonless, transparency 2/3, Antoniadi III, Bortle 8.
Even though it was easy to locate the nebula with the 25 mm eyepiece, I decided to wait until the constellation was a little higher in the sky. So at 2 am Carina Constellation was at its highest point and the Carina Cluster was at about 25° above the horizon. First, I set the telescope to NGC 3293 which is a lovely open cluster in Carina and it seemed to have some nebulosity in the background. This
cluster contains more than 50 stars in just 10 arc minutes field of view, in which the brightest star is a red giant of magnitude 6.5. Even the 25mm eyepiece provides a nice view of the cluster and the nebulosity is more evident, I decided to sketch it through the 10mm eyepiece, so a larger number of stars could be resolved: more than 20. It took me about 1 hour to sketch the whole FOV around NGC 3293. At around 3 in the morning I moved the telescope 2 degrees to the south-east and there it was, NGC 3372: the great Carina Nebula.

The brightest spot of the whole extended area of nebulosity is also the only distinguishable in the LP area. It glows like in a coma shape around a red-orange color star. When I started the sketch I didn’t even know what that star was; it just seemed to be shinning in a strong red-orange color similar to the color in Antares. I read that there was a unique star of 6th magnitude: η (Eta) Carinae inside the Nebula. In order to spot η Car in my sketch I decided to find it in Stellarium but unfortunately, Eta Carinae is not identified in Stellarium because it does not have a designation of Hipparcos catalog (1).

Looking in other sources, I found η Car position but something captured my attention: I had sketched the star as a red-orange star while the information about this star said that it was a supergiant blue variable star of spectral class B0. My first though was that maybe the orange color could be because the homunculus: two opposing lobes of expanding gas formed around the star, after a 1843 explosion known as Nova Carinae. However, it seemed like the homunculus color came from the star’s light, so I had to look deeply into why a blue giant was shining in red color. Finally, I found this explanation about the color of η Car: “The orange colour seems to result from emission lines in the star’s spectrum–mainly red H-alpha and blue-green H-beta"(2). 

Because I’m not currently involved in science at all, I do not quite understand why Eta Carinae is classified as a Blue variable giant star but I think that η Car has already burned up all its hydrogen and now it is burning Helium which causes its remarkable orange-reddish color. 

Anyway, this is a very exceptional star, as massive as at least 100 stars of our sun, other authors have said 150.  It has varied in magnitude from a 4th magnitude in 1677 to being the second brightest star in the sky in 1843 after Sirius, despite the fact that it is about 900 times farther away than it, to its present day magnitude of about 6: a wonderful marvel in the southern skies. 
After I processed each sketch individually, I decided to present them in the same scale size as if they had all been seen with the same eyepiece and also with the right distance from each other. Perhaps NGC 3293 loses some characteristics when the size was reduced as I had to put the same pixels in a smaller field.

Hope you can enjoy this marvelous creation of God in the southern skies.



Edited by Jennifer Steinberg  (editor in chief)


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