
Those in the northern hemisphere wishing to see a comet in the night sky currently have an excellent opportunity to do so. Comet NEOWISE (officially C/2020 F3 (NEOWISE)) is currently approaching Earth and will reach its closest point of approach on July 23rd, 2020, before starting its trip back out to the depths of the solar system.
Having passed around the Sun (reaching perihelion on July 3rd, 2020), NEOWISE has been an early morning, pre-dawn object in clear northern hemisphere skies. however, in the coming week it switches to being twilight object, potentially making opportunities to view it much better for many people.

The comet is a relatively “new” object in terms of its first observation – it was initially spotted on March 27th, 2020 by NASA’s Wide-field Infra-red Survey Explorer (WISE), a polar-orbiting space telescope. Launched in December 2009, WISE has been responsible for the discovery of thousands of minor planets within the solar system, and star clusters beyond. It is also a telescope with an interesting history.
Originally given a primary mission of just 10 months – the amount of time required to deplete the hydrogen coolant reserves the telescope needed to successfully operate two of its primary instruments – WISE was afterwards given a 4-month mission extension dubbed NEOWISE. For this mission it was tasked with looking for asteroids and comets that can come close to Earth (and are therefore known as Near Earth Objects, the “NEO” in the mission’s name). That mission drew to a close in February 2011, the telescope having completed an “all sky” survey, and it was ordered to place itself into hibernation, powering-off everything bar its communications link with Earth.

Then in August 2013, NASA decided to give the telescope a formal wake-up call, tasking it to resume its NEOWISE mission, this time with the emphasis on locating asteroids that may pose a risk of impacting Earth in the wake of the 2013 Chelyabinsk meteor incident. After a period of naturally cooling the vehicle and re-calibrating its instruments, WISE officially resumed NEOWISE operations at the end of 2013, and has gone on to observe more than 26,000 previously known objects, and has additionally identified more than 400 that had not been previously recorded, 25% of which have been classified NEOs.
C/2020 F3 (NEOWISE) is one of those 400+ “new” objects. After it’s initial identification, it was confirmed as a retrograde comet (i.e. it is travelling around the Sun in opposition to the Sun’s rotation), with a near-parabolic orbit. Its nucleus is believed to be about 5 km across, and covered with sooty material dating back to the origin of our solar system, 4.6 billion years ago. At the time of its closest approach to the Sun, the comet was just 43 million km from our star – causing speculation that it might not survive the encounter in one piece.
However, as it once again came into view from Earth, the comet had brightened considerably – to magnitude +1, while the out-gassing of material saw it develop two tails (although only one or the other tends to be visible in many photographs taken of it so far). The first is blueish in colour, and largely comprises gas and ion; the second is a more yellow-gold in colour, and thought to be largely made of dust.
At its closest approach to Earth, on July 23rd, the comet will be just 103 million km away, potentially offering the best time to see it – although binoculars will be required for the best view. However, it is not clear just how active the comet will remain as it moves away from the Sun, so there is a chance that the currently spectacular tail(s) extending from it may fade before then. As such, astronomers are recommending that the upcoming week should offers the “guaranteed best” opportunities to see the comet (local sky conditions allowing!).

Having been an early-morning object up until now, C/2020 F3 should switch to being an evening object from July 14th onwards, roughly 80 minutes after local sunset (during the nautical twilight period), and appear up to 20º above the local horizon, depending on your line of latitude in the north-eastern sky.
Beyond July 19th, the comet will remain visible increasing in altitude up to around 30º above the horizon for northern latitudes, and in the same part of the sky – but may see some reduction in brightness if the tail(s) do show a rapid fall-off due to cooling. After July 23rd, the comet will remain visible, but will fade more rapidly as it moves away from both the Sun and Earth. By August, it will likely only be visible via telescope.
Such was the comet’s close approach to the Sun, its its orbit was altered as a result of acceleration, increasing its orbital period from around 4,500 years to 6,800. So if you want to see it, this is the time to do so.
Continue reading “Space Sunday: Comet NEOWISE, Starship and Starliner”
















