Comet NEOWISE

One of the most spectacular comets in decades.

Comet NEOWISE has been entertaining space enthusiasts across the Northern Hemisphere. Although its official name is C/2020 F3, the comet has been dubbed NEOWISE after the Near-Earth Object Wide-Field Infrared Survey Explorer (NEOWISE) space telescope that first noticed it earlier this year. This “icy snowball” with a gassy tail made its closest approach to the sun on July 3 and is now heading back from whence it came: the far reaches of the outer solar system. Its long, looping orbit around our star ensures that after passing closest to Earth on July 23, Comet NEOWISE will not return for some 6,800 years making us the only humans to ever see it.

C/2020 F3 (NEOWISE) or Comet NEOWISE is a long period comet with a near-parabolic orbit discovered on March 27, 2020, by astronomers during the NEOWISE mission of the Wide-field Infrared Survey Explorer (WISE) space telescope. At that time, it was an 18th-magnitude object, located 2 AU (300 million km; 190 million mi) away from the Sun and 1.7 AU (250 million km; 160 million mi) away from Earth. (via Wikipedia)

We, observers in the Northern Hemisphere, hoped to catch a glimpse of Comet NEOWISE as it zips through the inner solar system before it speeds away into the depths of space. After its discovery Comet NEOWISE put on a dazzling display for skywatchers before it disappears, not to be seen again for another 6,800 years. NEOWISE passed dangerously close to the sun on July 3, but survived and has just hurtled past the Earth. The comet was closest to our planet on July 23, approaching within about 64 million miles.

Across the globe there were several observing opportunities over the last few days when it became increasingly visible shortly after sunset in the northwest sky. If one is looking at the sky without the help of observation tools, Comet NEOWISE will likely look like a fuzzy star with a bit of a tail, so using binoculars, a small telescope or in my case a dslr and lens, is recommended to get the best views of this once in a lifetime object. 

I was planning and hoping to see Comet Neowise but I had to contend with some challenges: 

• I could not find a spot away from city lights with an unobstructed view of the sky - Conora Virus Lockdown restrictions

• The best time to view was just after sunset, below the Big Dipper in the northwest sky, but because I was at home in the middle of heavy light pollution (Bortle Class 8/9) it was going to be very difficult.

• The skies had to be clear - and it had been raining every evening for a fortnight and the forecasts were more or less the same for the coming weeks.

The image above was captured on 21st July at 8pm under Bortle Class 8/9 skies using a Canon 7D Mark ii + EF 70-200mm f2.8 iii at 70mm, Aperture: f/2.8 | Shutter Speed: 6 seconds | ISO 100. The time window was very small and I was basically standing and waiting for the clouds to clear from about 6pm. And when I finally saw it I wasn’t sure I was actually looking at the comet which brings me to the topic of light pollution and the impact it is having.

The devastating impact of light pollution:

A recent study showed that about a third of the world’s population has never seen the Milky Way with their naked eye. But just a little bit over a hundred years ago everybody could see the Milky Way with their naked from the comfort of their garden or roof top. Today almost 70-80% of our population across the globe now lives in an area where they cannot see the Milky Way and there is a funny story about this around the earthquake in Los Angeles in 1994 which caused a power outage. The emergency services that morning were inundated with calls about a weird cloud in the sky. People thought aliens were coming!

That weird cloud turned out to be the Milky Way. They’d never seen it before and didn’t know what was going on and people were terrified.

The Bortle scale is a nine-level numeric scale that measures the night sky's brightness of a particular location. It quantifies the astronomical observability of celestial objects and the interference caused by light pollution. John E. Bortle created the scale and published it in the February 2001 edition of Sky & Telescope magazine to help amateur astronomers evaluate the darkness of an observing site, and secondarily, to compare the darkness of observing sites. The scale ranges from Class 1, the darkest skies available on Earth, through Class 9, inner-city skies. It gives several criteria for each level beyond naked-eye limiting magnitude (NELM). The accuracy and utility of the scale have been questioned in recent research.

The images on the right are light pollution maps of Hyderabad and my location which is a Bortle Class 8/9 - Inner City Sky - and a light pollution map of South India just to put things in perspective. As you can see there are very few true dark sky sites left in the south of the country. I use the Dark Sky app when I need to find dark skies followed by a whole sequence of apps to find the stars or galaxies. But most times I am restricted to doing star trails from wherever I am and some of these I have shared in my Photo Gallery.

The image below is an illustration of the different skies of the Bortle Scale with the star field visibility clear. Incidentally I have been beneath a Bortle Class 1 sky and the experience cannot be described in words. I could see the Milky Way and millions of stars, the ISS and the Star Link satellite train with my naked eyes. These were unforgettable times where once I was lying on my back with some good friends on a deserted beach near a temple town looking at a star field stretching from my head to my feet and once, fairly recently, on a bridge in sub zero temperatures hoping the temperature would drop to -15 degree Celsius or more so the difference in the air and water temperatures would create fog and my photos would have the “mood“.

But all that said I still wanted to photograph the comet if I got the chance, clouds, rain and light pollution be damned, and planned my angles and positions from my rooftop everyday - morning and evening. The planning involved looking at the weather forecasts multiple times a day for the opportune moment, poring over various sky charts to gauge the position of the comet like the one illustrated here on the right. This was a once in a lifetime opportunity and I was certainly going to try everything to get it.

Using apps like Star Walk 2 and Photopills to determine the shooting parameters as best as I could - low light, light pollution, preventing stars trailing, managing noise, shutter speeds, which lens to use for maximum intake of the little light there was etc. Constantly studying and monitoring the cloud cover on apps like Accuweather & Clear Outside and spending numerous 3am to 6am and 6pm to 9pm time windows on my rooftop and garden looking to the skies in the hope that they will clear.

Finally on the evening of 21 July I noticed the clouds starting to clear and basically ran up to the roof and set up in a hurry not wanting to miss any opportunity. I’d tried

• the 600mm - which gave me an extremely narrow field of view making it rather difficult to find what was effectively a dot with a faint tail;

• the 100-400mm - whose aperture was not going to let in enough light to have a manageable noise ratio.

I finally settled on the 70-200mm considering the wide aperture, almost no distortion and overall dependability and quality. I knew the focal length wasn’t going to be anywhere near what I wanted but the weather gods were not playing fair either. The image at the top was the one I was finally satisfied with and the one below was a little later hoping to get the same result at 200mm. The photo below has a faint tinge of the green coma of the comet and the one feature to look for - the presence of two very different tails: the dust tail, which appears bright, grey/white, wide and curved, as well as the ion tail, appearing comparatively faint, blue, narrow and straight. The dust tail is made of tiny fragments of the comet itself, coming in a wide variety of grain sizes and masses, while the ion tail is only made of extremely low-mass particles, tracing out the combined magnetic field created by the Sun and comet together. It is the best comet to grace our night sky in more than a decade. Here the dust tail is faintly visible but the already faint ion tail obviously isn’t. More information on comets and their tails is here.

I am still out looking for a better opportunity but it has been very cloudy these last few days and as the comet fades away so do the chances. Star charts to find Comet Neowise in the days to come.

In conclusion I want to include a video from the artist Seán Doran, whose work was on display at the Natural History Museum in London before the corona virus lockdowns.

He created the video by sourcing hundreds of images from NASA's database sourcing 550 images from the ISS archive, processing and interpolating the sequence to its real-time equivalent of seven minutes long. He also tweeted a time-lapse of the moment, highlighting the stunning event in just 15 seconds. Here the comet can be seen rising 3.10 minutes into the video.

The video shows the icy object Neowise trailed by its massive dust tail as it soars past our planet. The video also captured a simultaneous cosmic phenomenon — bright blue noctilucent clouds. These rare, high latitude and high altitude "space clouds" form when sunlight bounces off of ice particles in the upper atmosphere. 

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