Astrophotography in India

Astrophotography in India - II

Nebulas

In Calcutta, where I grew up, Ramkrishna Mission (RKM) operated a fantastic library in city’s Golpark area. The library’s amazing repertoire of books were often out of my financial reach. Of the library’s two sections the children’s section’s membership fee was a pittance, some 5 odd rupees a month. The library was some distance away from the apartment complex where I lived. Luckily for me I had a didi (elder sister) in the complex who was a member of the general section of the library. Piyali, who I would lovingly call Tumpa di, and I would take trips to that library a couple of times a month. The children’s library had a section that was ‘For Reference Only’, meaning that I could study those books in the library for as long as I liked, but could not borrow/take home. This section had an wonderful collection of books dedicated to astronomy and astrophysics. Among them were books showcasing photographs taken by various telescopes and I would spend hours there enchanted by that imagery! Nebulae were my favourite, resplendent with stars shining through the colorful assortment of clouds. I would spend significant time imagining the vast stretches of our galactic space sprawled within these wonders. My interest in science at this point of my life did not correlate with my performance in school. I regularly fared poorly in math and other exams. About two years before my 10^th board exams, I started enjoying the school physics, chemistry and maths materials and I started taking my studies very seriously. Unfortunately, by that time I also had matured past the age requirement to access the children’s section of RKM library. However, those initial days of pouring into star-sprawled books left a lasting impression on me.

During my school days, despite all my wishes, I was unable to get any hands-on astronomy experience. At that time, little did I know that I will be revisiting this passion a few decades later. During the summer of 2021 we faced a lockdown due to the second COVID19 wave. Forced to stay indoors due to the lockdown I was lazily star gazing one evening when I decided to give my old wish a shot. I got a DSLR camera and started photographing the stars. My experiments were a horrible failure! I found it incredibly difficult to capture the stars, which were sometimes hazy or, worse still, just a streak due to longer exposures. Moreover, pre-monsoon clouds had started rolling in and began playing havoc with my attempts. Monsoon season in Bangalore leaves astronomers with almost no opportunity to image the stars for the entirety of the summer and much of autumn. Yet, these attempts were not a total failure. I realized that for long-exposure photography with a DSLR camera, one required something called a star-tracker. The idea behind a star-tracker is rather simple. Earth’s rotation on its axis makes the stars rotate about an axis that passes approximately through the pole star. If you were to take a long time-exposure image of the region near the pole-star, you will see that the pole-star appears to be stationary, while other stars seem to rotate around it. This rotation, though slow for human eyes, is strong enough if you attempt even a 10-15 second exposure with a zoom lens (say 100 mm) to be noticeable. A star-tracker, when properly aligned, counteracts this rotation by moving your camera to keep pace with Earth’s rotation. This allows one to take very long exposure photographs of a particular location in the sky. For more details on the sky-tracker please refer to Essay on tracker.

So, during the monsoon season I spent a significant amount of time reading up on sky-trackers and their operation. This served me well once we got long-duration clear-skies again in early December. In the last week of December of 2021, I decided to focus on the Orion system. Thanks to an unhealthy diet of ‘Ancient Aliens’, this is one constellation that I was quite familiar with and December in Bangalore in a great time to view this constellation. In my initial images of the constellation, I realized that there was a ‘cloudy’ section below the belt! At that time, I had no idea that there are nebulae that can be viewed even with a simple DSLR (Canon 80D) and wide-angle kit lens. So my first guess was that something went wrong with the imaging, perhaps it was just a speckle of dust or a tiny high-altitude cloud. When I saw the same ‘cloudy’ area in pictures of the belt taken a couple of days later, I grew a bit suspicious and decided to do a little research. A few Youtube videos later, I was a wiser man! I realized that the ‘speckle of dust’ below Orion’s belt was nothing but the Orion nebula. The astrophotographer inside me was absolutely stoked by this realization. Over the next few days, I decided to observe that region of space with a 200 mm lens. On 29^th December 2021, with the tracker, I started taking longer duration images of 15 seconds, ISO 250 and F/6.3. I would later realize that it was not the correct ISO for me to take a picture at for these purposes. Figure 1, showcases my initial attempt to image the Orion nebula by stacking several individual 15 second exposures. A few days later, I changed to a different 200 mm lens, which operated at F/3.5 at 200 mm and increased the ISO to 400. By stacking many 10 second exposures, I was able to significantly improve upon by initial image (Figure 2).

Astronomically speaking, the Orion nebula is often referred to as M42. The ‘M’ stands for Messier catalogue and 42 is the order in which Messier catalogued the item. Charles Messier, an 18^th century French astronomer, catalogued a set of 110 astronomical objects. This catalogue comprises several spectacular examples of deep-sky objects - diffuse nebulae, planetary nebulae, open clusters, globular clusters and even galaxies! The very first object in the catalogue, is the Crab Nebula, whereas the Great Orion Nebula is 42^nd on the list, followed by De Mairan’s Nebula (M43). Figure 3 provides a size estimate of this region of space. In Figure 3, you can see both M42 & M43 as the latter is separated from M42 just by a dark lane of interstellar dust. M43 is illuminated by a massive star and this region is also called the miniature Orion Nebula due to its size and proximity to the Orion Nebula. The apparent brightness of the Orion Nebula has made it an easily identifiable object of the night sky and made it one of the most well studied deep-sky objects. The nebula is classified as a diffuse nebula referring to a region of space where inter-stellar dust and gas is illuminated by thousands of young stars. The region was closely studied by Hubble, and it was found to be stellar nursery housing many new stars and witness to inter-stellar fluid mechanical events such as bow-shocks around stars. The ‘nebulous’ region of hot-gas lighted up by the stars inside is about 1500 light-years away and spans a distance of about 24 light years as per astronomical calculations. For the Indian astrophotography enthusiast, December-February are the best times to catch a glimpse of M42.

My enthusiasm for astrophotography was already stoked when I ran into Vyom, who was struggling to photograph Orion on his own. He did not own a star tracker, so his attempts involved stacking (see essay on Stacking) with several short-duration images. He met with reasonable success on his own, but when we realized that we shared this fascination we decided to pool resources. A few days later, we clicked images of M42 & 43 with a 300 mm lens. Figure 4 shows a stacked and processed outcome of about 40 mins integration time with individual images of 60 second duration. The beautiful display of colors in this region come from ionization of various gases such as oxygen and hydrogen. It’s not an overstatement to say that the Orion nebula is a cosmic Holi that is happening thousands of years in the past. As we peer into our past with our telescopes, we can only imagine how this region of space looks ‘today’! In any case, Orion has introduced Vyom and I to the magic of astrophotography and for that we owe it our gratitude. Thank you Orion for being so colorful and bright.