Astro-Shed

This week brought with it a problem for the astrophotographer, the nearly full moon. The full moon is much like light pollution in that its reflected light causes the sky to brighten and this creates a situation where the contrast for dim objects is lost. The astrophotographer would normally have two options, image the full moon, or watch TV.

There is actually a third option that is available to us and that is to image with a narrow band filter. The filter blocks the majority of the light in the visible spectrum with the exception of specific wavelengths. This has the effect of the camera being able to “burn through” the moon light, or light pollution and image those wavelengths that the filter is designed for.

The target I chose for this night was NGC 1579, an emission nebula. I chose it for a few reasons. The first is was quite far away from the moon in angular distance. Choosing an object away from the moon reduces the effect of the moon’s interfering light. Typically you want to be no closer than 40 degrees. This object was more than 60 degrees.

The second reason I chose it was that it was high in the sky, nearly at the meridian at the beginning of the imaging session. This helps to reduce the impact of any light pollution from adjacent city light domes.

The last reason I chose NGC 1579 was that is was a an object that responded well to narrow band filters as it contained a large area of HII and OIII emissions. The HII areas came through well in the image as they are a lot stronger than the OIII signal. The OIII areas really only came out around the brighter stars in the image.

I tried to keep a very conservative black point on the image to preserve the weak OIII signal as best as I could. This ultimately gave a “smokey” appearance to the image but it also reveals that space is really not all black but filled with dusts and gases which have their own appearance. Over all I liked how the image came out.

So, if you are into astrophotography and you have hour hard drive full of image of the fullish moon, give narrow band a try. I think you will like the results.

Celestron SCT8″ x.63x scope, ZWO ASI533MC Pro camera, ZWO Dual-band filter. 90x180sec subs, 4.5 hours integration time over two consecutive nights.