NGC 6820...

Ha/Ha/SII/OIII = LRGB

Object: NGC 6820, Sh2-86 (containing star cluster NGC 6823)
Type: Emission nebula with open cluster
Constellation: Vulpecula
Distance: 6,000 light years

Date: July 10th/11th, 18th/19th. 2020
Equipment: ATIK 460EX with EFW2, Skywatcher f5.5 Esprit 100 ED refractor, Avalon Linear mount, guiding with Lodestar X2/PHD

Subframes: 16 x 600s Ha, 8 x 600s SII, OIII (2x2 binned) no flats/darks (hot pixel removal in Astroart).

Strictly speaking, NGC 6820 is a small reflection nebula near open cluster NGC 6823, discovered on August 7, 1864 by Albert Marth. The reflection nebula and cluster are embedded in a large faint emission nebula called Sh2-86, but the whole area of nebulosity is usually referred to as NGC 6820. Cluster NGC 6823 was discovered on July 17, 1785 by William Herschel

Map showing approximate image field of view

The rather obscure constellation of Vulpecula lies overhead during UK summer evenings, bounded within the three bright stars of Deneb, Vega and Altair, together called the "Summer Triangle". The whole area is rich in deep sky objects, lying as it does on the plane of the Milky Way, which itself can be glimpsed as a faint hazy band of light on those rare clear summer evenings. Vulpecula itself, although small, contains several objects of note, including M27, the Dumbbell Nebula.

Open star cluster NGC 6823 is about 50 light years across and lies about 6000 light years away. The centre of the cluster formed about two million years ago and is dominated in brightness by a host of bright young blue stars packed in a Trapezium-formed region about 1.3 x 0.7 light-years across. Outer parts of the cluster contain even younger stars. It forms the core of the Vulpecula OB1 stellar association.

The most striking feature in the image above is the trunk-like pillar of dust and gas protruding from the eastern side of the nebula towards the adjacent star cluster. The huge pillars of gas and dust are formed by surrounding gas and dust being pushed and eroded away by stellar winds and radiation from the brightest cluster stars. Dark globules of gas and dust (Bok globules) are also visible in the nebula.

Bok globules, named after the Dutch astronomer Bart Bok (who proposed their existence in the 1940′s) are dark clouds of dense cosmic dust and gas within star-forming regions in which usually star formation takes place. They most commonly result in the formation of double or multiple star systems.

I nearly didn’t bother processing the Ha data. The seeing on the night of July 10^th/11^th was terrible, and it was very hard to get a sharp focus on a star. The nebula itself also wasn’t as bright as I thought it might be and so retrospectively, 600 second unbinned exposures against a less-than-dark summer sky was perhaps rather optimistic. Sure enough, the nebula itself was faint and rather fuzzy due to poor focus and required a hefty stretch such that the result was overwhelmed by bloated stars (see below)...

Original Ha stack, with bloated stars

Just as an experiment, I decided to run the above image through Starnet, a piece of freeware that has the ability to remove stars from images of nebulae. I was rather surprised and pleased with the result (below).

Starnet rendition of stretched Ha stack...

I think that completely starless images of nebulae do look a bit weird however, so I blended it with an unstretched copy of the original stack that just more or less showed stars. The lack of stretching meant the starts hadn’t blown out and after a mild Gaussian blur (0.8, just to avoid a “painted-in” look), I dropped the star layer back onto the starless version in PSP "lighten" mode to produce what became the luminance/red channel (see image below).

NGC 6820 (Hydrogen alpha only)...

I finally got the SII and OIII subframes (600s binned) last nightin between a few clouds (18th/19th July) that enabled me to complete a colour rendition of this object. Colour RGB image was produced in Astroart (red - Ha, green - SII, blue - OIII) and finished in PSP, layering the Ha stack back over the RGB image as a luminance layer as the OIII/SII stars were a bit blown out. There wasn't much in the way of SII data at all, just a sort of general glow in the central area of the nebula.

References:

https://en.wikipedia.org/wiki/NGC_6820_and_NGC_6823

http://annesastronomynews.com/photo-gallery-ii/nebulae-clouds/ngc-6820-6823-by-robert-gendler/

https://cseligman.com/text/atlas/ngc68.htm#6820

Comet C/2020 F3 (NEOWISE)...

Object: Comet C/2020 F3 (NEOWISE)
Type: Comet
Constellation: Lynx
Distance: 134 million miles

Date: July 11th. 2020
Equipment: ATIK 460EX with EFW2, Skywatcher f5.5 Esprit 100 ED refractor, Avalon Linear mount

Subframes: 10 x 60s and 3 x 120 sec each for luminance and RGB, stacked and colour combined in Astroart, final processing in PaintShop Pro

It was with faint optimism that I swung the telescope down to this target at the end of a long imaging session. Initially the scope was pointing at a hedge, but the comet soon cleared my local obstacles and starting at around 3 a.m, I rattled off some exposures before the comet was quickly drowned out by the brightening dawn twilight.

Mk1 NEOWISE image...

The subs were messy (to say the least!), full of weird gradients and blobs brought on by the rapidly changing twilight conditions and some local horizon objects crossing the field as the telescope tracked the comet.

I processed the one minute frames to give (after a lot of work) a cleanish image, but still plagued with psychedelic background colours (see opposite). I was going to leave it at that, but today I thought I'd layer in the sky background from my first image of this comet, plus some data from the 120 second subs which showed a hint of the blue ion tail. The eventual result is the main image above, which I'm rather pleased with...

This comet is probably the most striking since Hale-Bopp back in 1997. Recent infra-red studies show that NEOWISE's nucleus is quite large, at around 5 km in diameter, hence its brightness. Hopefully it will remain as bright as it moves into the south-western evening sky (at a more civilised time!) over the course of the next few weeks...

Moon...

Waxing gibbous Moon...

Object: Moon (77% of full)
Constellation: Aquarius
Distance: 399523 km (248252 miles)

Dates: 11th. July 2020
Equipment: ATIK 460EX with EFW2, Skywatcher f5.5 Esprit 100 ED refractor, Avalon Linear mount
Subframes: 100 x  H-alpha (0.001s)

From the same session as the previous image, this one also nearly didn't make it on screen. I thought I'd grab a few subs of the moon as an afterthought, so I just slewed the telescope from my previous target (NGC 6820) down to the moon, which was lurking low down in the sky at about 16 degrees above the south-eastern horizon.

I made the mistake of not checking the focus before acquiring the subframes, and no amount of messing around in Registax or PaintShop will ever get back that missing detail...

I've put the final image up anyway, if only as a reminder of my own carelessness.

Comet C/2020 F3 (NEOWISE)...

Comet NEOWISE...

Object: Comet C/2020 F3 (NEOWISE)
Type: Comet
Constellation: Auriga
Distance: 160 million miles

Date: July 6th. 2020
Equipment: Canon 450D, Vixen 600mm 114 ED refractor, GPDX mount

Subframes: 34 x 1 sec @ ISO400,  processed in Registax.

Comet C/2020 F3 NEOWISE’s unusual name comes from NASA's Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE), which discovered the comet on March 27, 2020.  It is a retrograde comet with a near-parabolic orbit.  It survived its closest approach to the Sun on July 3, 2020 at perihelion 0.29 AU (43 million km) from the Sun, some 14 million km closer on average than the planet Mercury, an encounter that causes many comets to disintegrate.  Solar heating of this ball of ice and rock subjected it to temperatures of nearly 600C, causing it to dramatically brighten and shed gas and dust, giving rise to a cometary tail.  

My image above gives a fair representation of what the comet looks like through 6 x 30 binoculars before the dawn twilight gets too bright. 

Closest approach to Earth will occur 23 July 2020 at a distance of 0.69 AU (103 million km). This perihelion passage will increase the comet's orbital period from about 4500 years to about 6800 years.

Originally, NEOWISE was not expected to get much brighter than ninth or 10th magnitude, making it accessible only to those with good binoculars or small telescopes. During the spring, observers in the Southern Hemisphere followed the very rapid brightening of this object as its distances from both the sun and Earth decreased.  A consensus of observations placed it at magnitude +9.9 on May 10. Just under a month later, on June 7, the comet was on the far side of the sun, 73 million miles (117 million km) distant from the star and 147 million miles (236 million km) from Earth. It had increased 12-fold in brightness to a magnitude +7.2. As projected on the sky, the comet was scarcely 24 degrees from the sun (a closed fist at the end of an outstretched arm covers 10 degrees of the sky) and the two were rapidly closing together. Shortly thereafter, the comet was lost to earth-based observers in the increasing glare of the sun.

From June 22 through to June 27 however, the comet was within the range of the Solar and Heliospheric Observatory (SOHO). SOHO is a cooperative mission between the European Space Agency (ESA) and NASA. The spacecraft is stationed in a halo orbit around the sun-Earth L1 Lagrangian point, a position roughly 930,000 miles (1.5 million km) sunward of Earth. At this point in space, the orbital period of SOHO exactly matches the orbital period of Earth. From this orbit, SOHO is able to observe the sun 24 hours a day.

Using its Large Angle and Spectrometric Coronagraph (LASCO-3, which uses an occulting disc to block out the glare of the sun's disc from its images), NEOWISE could be monitored as it passed near to the sun.  During this time, the comet appeared to significantly brighten, just before it passed out of the field of the LASCO-3 camera. Comet NEOWISE also appeared to have developed a rather bright, albeit short and stubby forked-shaped dust tail.

Comets fall into two categories. "Common" comets are faint fuzz-balls that are visible only with the help of good binoculars or telescopes. At any time there may be perhaps eight or 10 such comets in our sky. Then there are the "Great" Comets, those that become bright enough to be plainly visible with the naked eye and accompanied by a striking tail of dust and gas. Unfortunately, such objects do not come around very often. In the average human lifespan, you may get a chance to see perhaps four if you are very fortunate.

The last great comet visible from the Northern Hemisphere was Comet Hale-Bopp in 1997, but is NEOWISE developing into one right now? Based on the very latest brightness estimates, Comet NEOWISE might fall just short of the criteria, though once it becomes evident in darker skies it should be quite obvious, especially away from light polluted cities.

Catching this comet required an early morning start, to see it emerge above the horizon for about 40 minutes before the glare of the rising Sun drowns it out.  At 3.45 a.m. the comet was a mere 8 degrees above the horizon and had just got above the roof of my next door neighbour's house.

Position of Comet NEOWISE on the morning of July 6th. 2020

The chart opposite shows its position in the sky that morning.

I was able to rattle off about 40 exposures, with one second ISO 400 exposures seeming to offer the best contrast between the comet and the rapidly brightening morning sky. The comet, with just a hint of its tail, was just visible to the naked eye in the morning twilight, but only because I knew exactly where to look, thanks to a laptop looking after the telescope pointing!  Through small binoculars, the tail was very evident and the jets on either side of the comet head could be seen.

I estimated its magnitude to be around 2, though its low elevation in the morning twilight makes such assessments difficult. It is certainly the brightest comet I have seen in the UK since Comet 17P Holmes back in October 2009.

Over the next few weeks, the comet draws away from the Sun, becoming an early evening object towards the end of July (see chart below).  It will be interesting to see if NEOWISE continues to remain bright as it passes by the Earth.

Track of Comet NEOWISE during July in 2020.

References:

1)  https://en.wikipedia.org/wiki/C/2020_F3_(NEOWISE)

2)  https://www.space.com/comet-neowise-july-2020-night-sky-forecast.html