Category: Deep Sky

New telescope

p>Whilst spending the weekend with my Dad, we stopped off at Astronomia in Dorking, Surrey. There on the shelf was a Williams Optics 70mm Zenithstar. I’ve been looking for something small and light to replace the Canon zoom lenses on the AstroTrac and this fitted the bill exactly. Having parted with some money, I took it home and contrary to known astronomical principles, the following night was clear!

First target, M51. This being a first attempt I wasn’t too sure what to expect at the longer focal length and the tracking wasn’t perfect so I finished the run with just 5 images of 3 minutes each. With the Canon 350D attached, the 420mm focal length yields 3.14″/pixel.

Deep Sky

AstroTrac

AstroFest saw me treating myself to something I’ve wanted for some time, an AstroTrac. Sunday evening was clear and frosty so I set the unit up on the top of a tripod on the path in front of my house. Leaving the Canon kit 18-55 lens on the 350D I took 10 3 minute exposures of Cassiopia at ISO 400 with the lens set at about 40mm. This produces a huge field of view that takes in the whole constellation down to the Double Cluster in Perseus (lower left of frame) and across to NCG 7789 (mid right).

Deep Sky Open Cluster

IC 2391 (Caldwell 85)

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.

Deep Sky

Epsilon Aurigae

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.

Deep Sky Nebula

The Horsehead in colour

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).

Deep Sky Nebula

The Horsehead reloaded

This is one of those areas of sky that will consume as much telescope time as time/money allow. A clear, moonless Australian sky enabled me to up the luminance frames to 30 minutes and also take a single 15 minute exposure through a hydrogen alpha filter.

Combining the luminance frames using SD Mask and a simple Digital Development stretch results in much lower noise than the original image post while keeping the star brightness under control. This was then aligned with the Ha image in Maxim DL, saved as a jpeg file and combined with the Ha image in Gimp.

The next step will be to add in the 15 minute exposures for each colour.

Deep Sky Open Cluster

M29 – Open cluster

While waiting for M82 to rise in the sky I filled in some time taking pictures of M29 in Cygnus. This is a small open cluster set against the backdrop of the Milky Way.

Being very high in the Southern sky this is in an area with very high field rotation so exposure times were very limited on the Alt-Az mounted telescope. I kept to 15 seconds @ ISO 1600 and ended up stacking 20 (car headlights are a particular problem with the telescope pointed in this direction).

Deep Sky Galaxy

Bode’s Nebula

Late in 1774, the German astronomer Johann Bode began to look for nebulae and star clusters. On the last day of the year he was credited with the original discovery of two galaxies, later to become known as M81 and M82. Just 38′ apart, they make a fine pair in the northern sky of Ursa Major. The target of this picture is M82.

An irregular galaxy, M82 shows signs of disruption and star formation caused by a recent encounter with M81 and is a strong radio source as well .

The Breckland 20″ telescope was used for this image with a Canon 350D. Sub frames were kept short at 20 seconds using ISO 1600 to avoid star trailing and this is the result of a stack of 14.

Deep Sky Nebula

Horsehead nebula

The constellation of Orion is home to many fine deep sky objects as well as M42 which featured in my last post. This one is IC-434, the Horsehead nebula. Probably the most photographed object in the sky it lies in the vicinity of the left star (Alnitak) in Orion’s belt (for northern hemisphere observers).

On the left hand side of the picture is the Flame nebula.

This is a work in progress and is a stack of the first four 5 minute exposures taken with GRAS-010, a TEC 140 and SBIG STL-11000M camera with a luminance filter.

Deep Sky Nebula

M42 – The Orion Nebula

Global Rent A Scope run a free trial introduction on one of their Australian telescopes. One click imaging; all you have to do is select what you want to image from the list of visible objects and the system will select an exposure, convert the camera picture to jpeg and email it to you when it’s finished. The result from a single 2 minute exposure of M42 is pretty good on it’s own, but the system also files a copy of the original FITS image on the FTP server. This extends the possibility of stacking multiple images for a lower noise picture.

So, after taking 3 images in a row I downloaded them and opened them in Maxim DL. What was immediately clear was just how good a job the system does in automating the jpeg image production. It took me several hours work to get close to the system’s image. Here’s the finished result, the telescope is a Takahashi Sky-90 with an SBIG ST-2000 XMC camera.