OT: Comet C/2020 F3 NEOWISE

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The image above shows comet C/2020 F3 NEOWISE, which is currently visible low on the northern horizon after sunset and before sunrise. From my 51 degree latitude, it is circumpolar, so visible all night, although very low in the sky. For the Northern hemipshere, this is probably the best comet since Hale-Bopp in 1997.

I took the image (or rather: images, as it is an image stack) last night around 00:58 UT (2:58 CEST) from Polderpark Cronesteyn on the outskirts of Leiden. It is a stack of 45 images of 0.6s exposure eacht, at ISO's 1600 and 4000, taken with a Canon EOS 80D + Samyang 2.0/135 mm on a fixed tripod (i.e. no tracking). The comet was only 8 degrees above the N-NE horizon at that time.

Apart from the bright bent yellowish dust tail, a hint of the straight, faint blue ion (gas) tail can be seen.

It was a very nice night (with owls calling), but a bit moist, with a carpet of low fog over the meadows. I had an USB dew lint and USB battery with me, and was glad I did. My glasses fogged over at times.

The comet is visible with the naked eye (even from my urban environment) with a few degrees of tail. It is impressive in 10 x 50 binoculars. the brightness is somewhere around magnitude +2.

The 2.0/135 mm Samyang turned out to be a superb lens for this comet, by the way. I am surprised by what I can achieve with it on this comet without a tracking mount.

OT: the bright fireball of 29 June 2018, 21:30:14 UT

image (c) Felix Bettonvil, Utrecht. Click to enlarge

Barely two weeks after an earlier brilliant twilight fireball discussed in a previous post appeared over the Netherlands, another bright fireball was observed, again in bright evening twilight. This fireball of about magnitude -6 occurred on 29 June 2018 at  21:30:14 UT (23:30:14 local time). It had a duration of over 3.6 seconds.

The fireball was photographically well covered this time, as it was captured by six all-sky meteor cameras (Borne, Bussloo, Dwingeloo, Ermelo, Utrecht and Wilderen) plus by an amateur astronomer from Kerkrade who was making a time lapse of the night sky. The image above (courtesy of Felix Bettonvil)  shows the fireball as it appeared over the camera station in Utrecht. Almost literally right over it: the lateral distance between the camera position and the nominal ground projected meteor trajectory is only 185 meters!

As several stations were equipped with an electronic or rotating shutter in front of the lens (see the interuptions in the trail in the image above, at 10 breaks/second), there is speed information for this fireball as well. In fact, it delivered a very fine deceleration curve (data from stations Borne, Utrecht and Dwingeloo), showing how the meteoroid rapidly slowed down upon entry into the atmosphere due to friction with the atmosphere:

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The fireball entered from the south-southeast with a  speed of 21.5 km/s and under a low 27 degree entry angle. It first became visible at 80 km altitude over the Betuwe area near 5.416 E, 51.822 N. It ended at 43 km altitude over the western suburbs of Amsterdam, near 4.837 E, 52.360 N, with an end speed of 9 km/s. End altitude and end speed point out that nothing was left at that point: there are no meteorites on the ground.

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The radiant of the fireball is located in Scutum: the geocentric radiant is at RA 276.4, DEC -11.4, with a  geocentric velocity of 18.2 km/s. The resulting orbit is an Apollo orbit with an orbital inclination of 7 degrees, an orbital period of 2.15 years and aphelion at 2.7 AU. The object was hence of asteroidal origin: a very small piece of asteroid.

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Acknowledgement: I thank Mark-Jaap ten Hove, Johan Pieper, Koen Miskotte, Jean-Marie Biets, Felix Bettonvil and Peter van Leuteren for making their imagery available for analysis.

OT: the slow, 13.8 second duration earthgrazing fireball over the Netherlands of 28 Nov 2016, 04:40 UT

the long duration (13.8 s) fireball of 28 Nov 2016, 4:40 UT 
image (c) Jos Nijland, Benningbroek, NL - click to enlarge

In the early morning of 28 November 2016, near 04:40 UT (05:40 am local time), a bright, slow fireball with an extremely long duration occurred over the Netherlands.

The image above was captured by the all sky meteor camera of Jos Nijland in Benningbroek and shows how the fireball trajectory spanned much of the sky. This camera was  equipped with a rotating shutter, and the number of breaks visible in the trail amount to at least 13.8 seconds visibility. That is very long for a fireball.

With such slow, long duration fireballs, one of the first questions asked usually is: is it a meteor, or is it the re-entry of artificial space debris? In this case, the analytical results clearly show it was not an artificial object, but a meteoric fireball of asteroidal origin - i.e. a small chunk of asteroid entering the atmosphere.

A total of 7 all sky photographic cameras captured the fireball: apart from Benningbroek (Jos Nijland) shown above,  it was also captured by stations Ermelo (Koen Miskotte), Oostkapelle (Klaas Jobse), Utrecht (Felix Bettonvil), Bussloo (Jaap van 't Leven), Borne (Peter van Leuteren) and Twisk (Marco Verstraaten). Benningbroek also captured the last few seconds of the fireball on video with a CAMS camera. Koen Miskotte in Ermelo in the center of the Netherlands also observed the fireball visually, estimating it magnitude -5. He reported fragmentation.

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The photographs allow to reconstruct the atmospheric trajectory, speed, radiant point and heliocentric orbit of this fireball, and whether something survived at the end or not.

The fireball appeared between 04:40:26 and 04:40:40 UT. It entered the atmosphere on a grazing shallow angle of only 11.2 degrees. The trajectory was over 180 km long - the average trajectory for all stations combined is 183 km long, but some stations captured an even longer part, with Benningbroek topping all with 212 km trajectory length! The fireball started over the North Sea at an altitude of 77 km near 53.0 N, 3.1 E (average of all stations), and moved on an almost due West-East trajectory, over the tip of North Holland province and Lake IJssel, ending at 42 km altitude over the northern part of the Noordoost Polder near 52.8 N, 5.7 E.

Four of the 7 stations were equipped with a rotating shutter in front of the lens, allowing speed reconstructions. Combined with the radiant point determination, this yields the orbit in the solar system.

The fireball entered the atmosphere with an initial atmospheric speed of 15.45 km/s. At the end of the trajectory, at 42.3 km altitude, it had slowed down to a terminal speed of 9.3 km/s. At that point, nothing was left of the original meteoroid: no meteorites reached the ground, it had completely ablated away. The deceleration curve obtained is actually quite nice:

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The apparent radiant of the fireball was low in the western sky, at RA 53.2 degrees, DEC +13.0 degrees in Taurus. The geocentric radiant (the radiant point corrected for amongst others gravitational influence) was at RA 43.8 degrees, DEC +0.4 degrees. The geocentric speed was 11.1 km/s.

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The resulting heliocentric orbit is that of an Apollo asteroid, with perihelion at 0.874 AU, aphelion squarely in the asteroid belt at 2.76 AU, an orbital eccentricity of 0.518 and an orbital inclination of  4.9 degrees.

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