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| 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.
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| 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.
