Beginnings and endings and the rise of the robot: cosmic clouds and bubbles

This is the third in a planned series of four image-rich posts within which I hope to share my progress in astrophotography; the first is here and the second is here. I decided to write these posts as a means of taking stock of what I’ve achieved in the years since taking up this challenging hobby in my mid-60s. There’s nothing like writing about something to sort out one’s thoughts. The 'backstory' to this current short series may be found spread through several earlier posts: they'll be obvious if you peruse the blog. An alternative to reading those would be to watch a recording of the talk I gave in January 2025 which summarises the earlier stages of my journey: there’s a link to the YouTube capture in the first paragraph of ‘Climbing over Failure’.

The type of astronomical target I’ll introduce here, via some more of my images, are the nebulæ (- nebulæ is the plural of nebula). A nebula is a cloud of gas and dust in space which, in the context of astrophotography, either
o blocks the light from the stars behind it getting to us or
o reflects the light of one or more bright stars between it and us or
o appears to emit light which has, in fact, been generated within it by bright stars.
These are dark, reflection and emission nebulæ respectively. I have captured images of all three types, together with a subset of nebulæ associated with material that has been ‘puffed’ out by an ageing star or in some cases thrown out violently as the star explodes as a supernova.

By the time you get to the fourth post in this series – I’m being optimistic you understand: of your reading stamina and of my ability to sit down and write it – it will have become obvious that there is a progression in scale. Every image I have shared up to and including in this post resides within our galaxy, the Milky Way; their distance from us is therefore limited to the size of the galaxy. The Milky Way has a diameter of approximately 100,000 light years (ly) across its disk but is only about 1,000 ly [i] thick. This constrains the distance from my back garden to the objects I’ve been imaging, be they binary star systems or star clusters or nebulæ. However, the size of the object itself is tending to increase and in the case of nebulæ we might be talking of objects that are over 100 light years across.

Following the pattern of my first two posts in this series, what follows is a collection of my images; the captions will provide additional information. The quality of the images varies simply because my equipment, software and associated proficiency and skill have evolved over time. One qualitative change came with the arrival of my entry-level pet robot this Summer – a fully automated imaging system having a wider field of view than my more conventional telescopes. One of its attributes is therefore the ability to capture larger-scale targets, especially when used to create a multi-panel mosaic. However, let’s start with images derived from the deep sky setup used for the previous post on star clusters …

This is NGC7023 [ii], the Iris Nebula – yes, they all have names – which resides within the constellation Cepheus. It’s about 1,300 ly away and is 6 ly across. Most of the nebula is dark; even with my limited image processing skills one can make out extensive patches of the sky with few visible stars or none. Even where some starlight gets through the stars take on a sort of reddy hue; this is caused by the same light scattering processes that gives us our red sunsets and dawns on Earth: the blue end of the visible spectrum being scattered in all directions whilst the longer wavelength red end is far less spread out. The bright blue colour at the nebula’s centre – which is what gives it its name – is reflected light from a star (HD200775) lying between us and the nebula.

The principal nebula in Orion, M42, can be seen with the naked eye in an area without light pollution (unless your eyes have reached the age mine have!) and certainly with binoculars. However, all you’ll see is a fuzzy white blob as our colour vision isn’t great in low light levels. Stick a telescope and astronomy camera in front of it and so much more is revealed. It’s about 1344 ly away and approximately 25 ly across; it covers twice the area of the Moon (or Sun) in the sky, so if we could make it out by eye it would surely be an awesome sight. The really bright core region is being illuminated by a group of four young hot stars, the Trapezium. Indeed, the Orion Nebula is our closest region of active star formation.

 

Two versions of the same thing taken a few months apart; the right hand image is oriented about 90° counter-clockwise compared to the image on the left. This is the Bubble Nebula, NGC7635, about 7,000 – 11,000 ly away (7-11 kly) in Cassiopeia. The radiation from a massive young hot star, SAO 20575, both illuminates and ‘blows’ away material [iii] which comprises the large expanse of dust and gas in which it sits: this forms the bubble we perceive. The boundary of the bubble is in essence the shockwave between the solar radiation and the nebula. By the way, the red glow, which is a characteristic of nebulæ, is due to the dominant emission colour of hydrogen. (For more – much more – on emission and absorption lines please see my videos on the topic here and here) Apart from their apparent rotation with respect to one another, which is partly a camera framing issue and partly due to the changing sky as the year progresses, you will notice a difference in the apparent star numbers and brightness. Because this patch of sky is in the direction of the Milky Way’s disk it’s particularly dense with stars; the further one looks out from the disk the less busy the view. This effect can obscure the object we’re focused on and to counteract this I employed a piece of software called StarXterminator which allows me to remove the stars digitally, process the fainter nebula and then add the original stars back in with reduced brightness. I use it as a plugin within AffinityPhoto2.

 

Enter the robot. My relatively recently acquired Dwarf3 sets the Bubble Nebula in its broader context within Cassiopeia. Not only do we get the wider nebula but two star clusters (M52 above left and NGC7510 bottom right), part of the Lobster Claw Nebula (NGC6357, bottom, left of NGC7510) and a bright region of massive star formation (NGC7538, upper right).

 

Another shockwave caused by the resistance of a cloud of dust and gas to the radiation, or solar wind, of a star (HD 192163) within it, which became a red giant ¼ million years ago. This is the Crescent Nebula, NGC 6888, in the constellation Cygnus. It’s about 5 kly away.

 

Now that we’ve established both the origin of the red colouration of hydrogen-rich emission nebulæ and the fact that my pet robot has a wide field of view, I could more easily image this extensive area of nebulosity in the vicinity of a bright star called Sadr in the constellation of Cygnus (γ Cygni, about 1,800 ly from us). The Crescent Nebula (see above) is nearby.

 

Still in Cygnus, the North America Nebula (NGC7000) is named because it resembles … guess what? To the right, in the lower half, is the Pelican Nebula: long beak, looking in the direction of the ‘Gulf of Mexico’.

If we crop in towards ‘California’ we can pick out more clearly the Cygnus Wall – a bright star-forming region which has been sculpted by solar radiation.

 

Moving from star-forming to star endings, this is The Eastern Veil Nebula (NGC6995). Together with its Western counterpart and a lot of other material in between it originated in the supernova explosion of a large star more than 10,000 years ago. The stellar material has expanded to cover approximately 3° of the sky, so ~6 times the Moon’s diameter. Its colour comes from hydrogen emission of course, but also from the oxygen and sulfur created in the original star. Nearby stars have sculpted its shape beautifully.

 

The Crab Nebula (M1, in the constellation Taurus) is the remnant of another supernova. This explosion was witnessed in recorded history: Mayan, Japanese, Arab and Chinese astronomers observed it in 1054 AD. It’s still expanding at around 1,500 km/s. It is approximately 6.5 kly away. This was the first nebula I attempted to image; I keep meaning to go back and do a better job but new shiny challenges seem to propel me forward instead.

A smaller aging star, the size of our Sun for example, might not explode as a supernova. Instead, it may swell up and slough off its outer layers as its hydrogen stocks deplete and then shrink back to become a dwarf of some kind. The ejected material becomes a planetary nebula. This example is the Ring Nebula, M57, in the constellation Lyra and at its centre now sits a white dwarf. It is 2,570 ly away and has been expanding for an estimated 1,610 years.

The Owl Nebula, M97, is another planetary nebula; it’s within the constellation Ursa Major. The qualitative difference between this and the Ring Nebula is that the star went through more than one period of throwing material off. The inner shell of material is more barrel-shaped than spherical and the result is this very distinct form to the nebula. It is ~2030 ly away and has been expanding for about 8,000 years.

The Dumbbell Nebula (M27), another planetary nebula, is expanding from a white dwarf ~1360 ly away and is in the constellation Vulpecula. From its measured rate of expansion, one may calculate its age as being ~10,000 years. Why, you might ask, is it still glowing after all this time? Well, space is effectively a giant vacuum flask: there is no conduction or convention to carry heat energy away only radiation – and this is exactly what we are detecting.

The image above provides an excellent segue into the fourth and final post in this short series, in which I’ll present my images of truly huge and distant objects imaged from my garden: galaxies. In the centre of the image above sits the spiral galaxy NGC7331, which is at a distance of almost 44 million light years (Mly). The reason I include my image of it here is that on 14th July this year there was a supernova observed in the galaxy. It was designated SN2025rbs. Unfortunately, the star that exploded sits close to the core of the galaxy and is therefore harder to resolve using amateur equipment such as mine. However, it was almost as bright as the galactic core so, if you look carefully at the enlarged inset, you should be able to make it out.

Until next time …

Endnotes:

[i]    In other words, light emitted during the reign of King Canute (or Cnut, ruler of England, Norway and Denmark) from a star at the ‘top’ of the galaxy will be reaching the ‘bottom’ about now. By comparison, our Sun’s nearest neighbour star is a little over four light years (ly) away whilst its most distant planet, Neptune, is a mere four light hours away. The Voyager probes, which have been travelling at prodigious speeds since their launch almost half a century ago, are still less than one light day away.

[ii]   There are several catalogues in existence which list notable objects. Arguably the most widely used within the amateur astronomy community are:
M, the Messier catalogue of non-cometary objects (Catalogue des Nébuleuses et des Amas d'Étoiles) begun in 1774 with the work of Charles Messier and
NGC, the New General Catalogue of Nebulae and Clusters of Stars compiled in 1888 by Johan Dreyer. 

There are analogous catalogues for stars, for example:
HD, the Henry Draper catalogue (1918–1924);
SAO, the Smithsonian Astrophysical Observatory catalogue (1966);
HR, the Harvard Revised Photometry Catalogue (1930 and 1983).

[iii]  As an aside, I note that there is a dynamic balance in the early life of a star between the rate at which material in a proto-planetary disk is pushed away by solar radiation and the chance that it clumps together and eventually forms a solar system. The outcome is decided within a relatively brief period after the star’s formation – a period measured in millions of years.