Observations

Frank images the Trifid Nebula

Trifid Nebula imaged by Frank Loveridge

Trifid Nebula imaged by Frank Loveridge

The Trifid Nebula, Messier 20, is one of the best known objects in the sky. It is a star forming region about 9000 light years from Earth. Its three dust lanes divide it into three and explain its name. Sydney City Skywatchers member Frank Loveridge showed the impressive image above at the group’s most recent monthly meeting.

The red colour in the image is from hydrogen atoms excited by ultraviolet light from the star near the centre – this is a process similar to that in fluorescent tubes in homes and offices. The dust lanes are dark as they are in front of the glowing gas and are seen in silhouette. Surrounding the red area there are blue areas. Here the light has insufficient energy to excite the hydrogen atoms and so light is only scattered. This scattered light is predominantly blue as that colour is scattered more than red light – hence the blue sky on Earth.

Frank writes about his image:

The Triffid Nebula has the Messier catalogue number of M20 and a New Galactic Catalogue number of NGC 6514. It is both an emission nebula and a reflection nebula.

The image was taken recently from the balcony of my house on the northern beaches of Sydney. It is a series of 8 light images being 4 x 10 minute exposures and 4 x 5 minute exposures. In addition there are 8 dark images aligned with these light images. A dark image is an image taken with a cap on the telescope so as to match a light image with data on it so as to balance the amount of signal noise generated on the camera ccd chip. This may be difficult to understand but there is no easy way to explain the purpose of this process. There are also flat images used in the process as well but that can be explained at a later date. All of the images are then stacked one on top of each other to produce one final image with the data of all the separate images in it.

I use a stock standard Canon 1000D DSLR camera attached to a 127mm aperture refractor telescope. This is my main imaging telescope. I also have a smaller telescope with a different camera on it to guide the main imaging telescope and it is all set up on an equatorial mount.

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