Observations

Frank images the spectacular southern object Eta Carinae in its full glory

Eta Carinae imaged on 25 April 2009, courtesy Frank Loveridge

Eta Carinae imaged on 25 April 2009, courtesy Frank Loveridge

At the May 2009 meeting of the Sydney City Skywatchers, a new member, Frank, showed this magnificent image of the Eta Carinae Nebula. It immediately caught my attention as it is an exceptionally impressive image with great details and colour. In addition it seems to have been the favourite object for Henry Chamberlain Russell, the director of Sydney Observatory from 1870 to 1905 and a pioneer of celestial photography. Russell took numerous images with different cameras of the object he called by its old name of Eta Argus.

Frank writes about his image:

This image was taken using a 127mm Apochromatic Refractor telescope from the balcony of my house at Palm Beach on the Northern Beaches of Sydney on the 25 April 2009.

It was taken with a Canon 1000D Digital SLR camera at ISO 800. 4 x 300 second images went into making this one image so that is 20 minutes of data. I also programmed the camera to automatically subtract dark frames from the light frames to help remove unwanted signal noise.

I use an 80mm guide scope. This is connected to my computer and my EQ6 mount running PHD guiding software. I have to set up the equipment every time that I want to use it and do a Polar alignment and drift alignment so that I am pointed very close to the South Celestial Pole before I start guiding.

The images are stacked together with Deep Space Stacker which is a freeware product available on the internet and then dark levels are set with Photoshop.

The colour in the image is the colour of the object as it was taken by the camera and has not been manipulated in any way.

Eta Carina (or Argus) imaged by Henry Chamberlain Russell in about 1891 with the 33-cm lens of the Sydney Astrographic Telescope.

Eta Carina (or Argus) imaged by Henry Chamberlain Russell in about 1891 with the 33-cm lens of the Sydney Astrographic Telescope.

Eta Carinae Nebula is a cloud of gas and dust surrounding the massive star Eta Carinae. A variety of notable features can be seen in the images such as the Keyhole Nebula just above centre. It is of interest to compare the appearance of the nebula in the two images taken over a hundred years apart as in Russell’s time there were serious discussions about possible changes.

To the bottom right of the keyhole we can see the star Eta Carinae itself. This star is of considerable fascination as it is one of the most massive stars known to astronomers. With a mass of around 100 times the mass of the Sun, it is a prime candidate to become a supernova or explode. Fortunately, it is 8000 light years away so that though the explosion should make the star easily visible in the night and possibly the daytime sky, it will not be dangerous to the survival of life on Earth. According to some recent suggestions the star is double, with two massive stars circling each other.

Thanks Frank for a great picture. Keep photographing the sky and hopefully, share some more images with the readers of this blog.

2 responses to “Frank images the spectacular southern object Eta Carinae in its full glory

  • Well done Frank,
    great rendering of the regions lit by H-alpha (red light) and those fluoresing in OIII (green/blue), or is Hydrogen Beta or Gamma involved?. This colour fidelity is really only possible with digital detectors I suspect. Can we learn some moredetails of Frank’s equipment etc. How did he prevent central regions from overexposing?

    Nick, does the term “fluoresence” correctly describe the process whereby the nebulae emit light? Im thinking that UV from very young nearby stars is what stimulates the fluoresence – or am I mistaken?

    Harry

    • Hello Harry. Yes, you are quite right most of the radiation from bright nebulae – clouds of mainly hydrogen gas and dust – is from fluorescence. This is a similar process that happens in fluorescent tubes in offices and suburban streetlights where it is electric current that excites the atoms to higher energy levels and they drop back to lower levels by emitting photons of light. In nebulae it is energetic ultraviolet radiation UV that excites the atoms. Different energy levels are excited and so different colours are emitted depending on distance from the source of UV radiation. Sometimes though the light from nearby stars is not energetic enough to cause fluorescence so that the light emitted is blue scattered light.

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