Andrew’s Astronomy Blog

In the constellation Vela in Southern Skies is a large open cluster that’s visible to the naked eye. Comprising about 30 stars spread over a 50 arc minute area, it lies at a mean distance of about 580 light years. The individual stars were formed around 36 million years ago.

The individual sub-frames are all of 3 minutes (2x luminance, 1x red, 1x green, 2x blue). To try and get the star colours correct I used a simple utility called eXcalibrator from http://bf-astro.com/index.htm. This uses catalog information from NOMAD to calculate scaling values for the RGB channels. In this case, adjustments were minor (R - 1.0, G - 0.97, B - 1.22). The telescope used was GRAS-10, a TEC-140 refractor.

Since originally posting this image I’ve purchased a copy of Carboni’s Astronomy Tools and added some diffraction spikes to the brightest stars.

Epsilon Aurigae, also known as Almaaz, is a super-giant F0 star in the constellation Auriga. This star is truly massive, being 100 to 200 times the diameter of the sun and 50,000 time more luminous. What is slightly unusual about this star is that every 27 years it’s light dims for a period of about 2 years and it’s considered that this is caused by the star being occulted by a companion object. The current cycle began back in August and once a week I’ve been taking a picture of it along with two adjacent bright stars as comparisons.

The results for 2009 are summarised in this graph:

My choice of comparison stars is not ideal as they themselves may be slightly variable so for future observations I’m including the star which is more usually used (lamda Aurigae) in my images. Global-Rent-A-Scope also upgraded the camera on this telescope at the end of December so I’m currently waiting for some updated calibration frames.

The graph is showing a nearly linear decrease in magnitude which is due to reach it’s minimum very soon. The nature of the companion object is currently under investigation and the present theory is that it is a large dust disk. Hopefully, the results from the study of this occultation will solve this mystery.

Taking advantage of the fact that narrow band imaging is relatively unaffected by a full moon in the sky (and the 50% discount in telescope cost) I added another two 15 minute Ha exposures to my collection of the Horsehead. Then the pain-staking process of combining the individual frames to make a single pleasing colour image could begin.

All the frames were calibrated and aligned  in Maxim DL and the red, green and blue frames combined to make a single RGB image. A Digital Development Process stretch was then applied to all images and they were saved as 8-bit tiff images for further processing in Gimp (my favourite open source image processing software).

The bright star is Alnitak, the left hand star in Orion’s belt. The radiation from this star lights up a hydrogen gas cloud making it glow red and the Horsehead itself is a dark cloud of gas and dust silhouetted against the bright background. The Flame nebula (NGC 2024) is formed in a similar manner. Just below the Horsehead is NGC 2023, a bright reflection nebula. 1500 light years away, the Horsehead is some 3.5 light years in height (or 2×10¹³ miles high).