78.5 hours exposure on M81 and M82

 Deep Sky, Galaxies, General Astronomy, Image Processing  Comments Off on 78.5 hours exposure on M81 and M82
Nov 102021

This is the first image I have posted using data from my new remote telescope setup in Spain and it is, perhaps, the ‘deepest’ image I have ever processed. I have only recently taken over this system after I purchased it from First Light Optics who also kindly bequeathed me all their images taken over the last year or so that the system has been in operation. The images used to make up this image were taken over April and May 2021 when M81 and M82, both in Ursa Major, were higher in the sky. The larger galaxy on the left is M81 – Bode’s Galaxy and the smaller one is M82 – The Cigar Galaxy.

M81 and M82 were both discovered in 1774 by the German astronomer Johann Bode who reported his observation to Charles Messier who then added them to his famous catalogue. Both galaxies are about 12 million light years away (which is 114 million million km or 770,000 times further away than the Sun).

Here is the colour image; click on it to see a bigger version. More details follow the image below:

M81 and M82 in the Integrated Flux Nebula

What else can we see in this image? Directly above M81 is a blue patch – you can see it better in the full sized image. This is a satellite galaxy to M81 called Holmberg IX. This is a dwarf, irregular galaxy and based on the observed age distribution of stars it contains it is thought to have formed within the last 200 million years, making it the youngest nearby galaxy known. This would explain the blue colour as the stars within it will be young and hot.

The faint wisps all around the galaxies are all part of the Integrated Flux Nebula (IFN), so-called because it shines by the total (integrated) light of all the stars in our Milky Way Galaxy. The IFN lies beyond the main body of our galaxy, and is illuminated by the whole thing. It is incredibly faint and only recently discovered in 1984 by the IRAS satellite. To show it better, I have stretched the histogram of the luminance channel of the above image even more. This monochrome image is shown below:

For those interested in the technical details of the image acquisition and processing, the image contains a total of 78.5 hours of exposures made up as follows:

Red Filter112 x 5 minute exposures
Green Filter112 x 5 minute exposures
Blue Filter98 x 5 minute exposures
Luminance Filter287 x 5 minute exposures
H-Alpha Filter83 x 20 minute exposures

The above table shows the actual number of exposures that were used in the integration to make the final image. Many more were rejected because of satellite or plane trails, or thin cloud etc (for example 73 of 360 L images were rejected). All images were calibrated with bias, dark and flat frames and all processing was performed in the amazing PixInsight software.

 Posted by at 11:37 am

The Heart Nebula revisited

 Deep Sky, Image Processing  Comments Off on The Heart Nebula revisited
Nov 062021

A few posts back, I showed a narrowband image of IC 1805 – The Heart Nebula taken during the full Moon. It looked rather pink as the H-Alpha signal is so dominant and overpowers any greens and blues that the OIII signal might provide. Here’s a new, differently processed, version (note: I’ve also flipped it so that the heart is the right way up!). Read below to find out what I did differently.

Using the amazing PixInsight software, I split the R, G and B channels apart. This meant that the resulting red channel contained just the H-alpha signal, but the green and blue channels shared the signal from the OIII emissions. I then made a new O channel by combining the green and blue channels using a formula of (2*G + B)/3 which gave a bias towards the better image I saw in the green.

Calling the red ‘H’ and the new combine green and blue ‘O’, I stretched their histograms, but also used a range mask on the O to stretch it much more (the mask prevented the background from becoming too noisy). This was the key to getting more blue in the resulting image. Then I recombined using HHOO to correspond to LRGB. Now you know why these are called false colour images!. However, all the data is real, it’s just a personal preference.

I think the result has a more 3D effect.

 Posted by at 3:15 pm

Cosmic Diamond Dust and the Iris Nebula

 Deep Sky, General Astronomy  Comments Off on Cosmic Diamond Dust and the Iris Nebula
Nov 052021

Here is my latest image from here in Ham, near Selsey. This is the beautiful Iris Nebula (NGC 7023) in the constellation of Cepheus. I took the images last night in a lovely clear, moonless sky from astronomical dusk to dawn. In all, 120 x 5 minute exposures were captured and I only had to throw away three of them because of very bright plane or satellite trails. This time, because there was no Moon, I was able to use the full bandwidth of a luminance filter on the QHY268C one-shot cooled colour camera.

The Iris nebula is an example of a Reflection Nebula. This is what Wiki has to say about these kind of objects:

In astronomy, reflection nebulae are clouds of interstellar dust which might reflect the light of a nearby star or stars. The energy from the nearby stars is insufficient to ionize the gas of the nebula to create an emission nebula, but is enough to give sufficient scattering to make the dust visible. Thus, the frequency spectrum shown by reflection nebulae is similar to that of the illuminating stars. Among the microscopic particles responsible for the scattering are carbon compounds (e. g. diamond dust) and compounds of other elements such as iron and nickel. The latter two are often aligned with the galactic magnetic field and cause the scattered light to be slightly polarized.

So, we can see that there could be diamonds in that dark dust!

Here’s the image. As always, click on it to see a much larger version in a new window.

The Iris Nebula
 Posted by at 4:12 pm

The Orion Nebula and the Horse Head

 Deep Sky, Image Processing  Comments Off on The Orion Nebula and the Horse Head
Nov 052021

The Great Orion Nebula (M42) and the nearby Horse Head Nebula (IC 432) are amongst the most photographed objects in the deep-sky. Of all the images I have taken of these beautiful nebulae, this is my favourite because it encompasses both of them in a single wide image, but still has enough resolution to show the intricate details and also the darker dust clouds in the Orion Molecular Cloud Complex.

Click on the image below to see a bigger version.

I took this image in January 2016 whilst Sue and I were renting a rural house in Southern Spain for the Winter months. The skies were lovely and dark at the house which was in the Cabo de Gata region of Andalusia.

More remarkably, I used a non-cooled DSLR camera in the form of my modified Canon 6D. Modified means that the filter that blocks the deep red part of the spectrum has been removed which makes the camera more sensitive to the Hydrogen Alpha emissions in these nebulae. Astronomers call this a filterectomy!

I took 60 x 4 minute exposures and then 30 or so shorter exposures of 30 and 15 seconds for the brighter core of M42. The shorter exposures where blended in to the rest of the longer, deeper exposures making this image and example of an High Dynamic Range (HDR) image. Without blending in the shorter exposures, the core would appear completely blown out and the finer structures would have been lost.

All processing was performed in PixInsight, including the initial calibration using bias, dark and flat frames.

 Posted by at 1:34 pm