By John Pickering 09/03/2021

Apophis on a trip to down-town Auckland


On Friday night, 5 March 2021, the “God of Chaos” sped past our planet.

The asteroid Apophis, or “God of Chaos” as it is known, made a close approach.  Bigger than the Sky Tower (about 370m diameter) and faster than a speeding bullet (4 km/s or about 14,000 km/h) it would surely be a spectacular sight if it hadn’t been so far away (16,000,000 km).  Fortunately, to keep you all safe, I was watching with a new kind of amateur telescope, the Unistellar eVscope (enhanced Vision scope).*  The thin streak in the photo below shows the movement of Apophis relative to the background stars.

Apophis will come around again in April 2029, but much much closer.  Skimming the Earth under 3 Earth diameters away (~36,000 km), possibly disrupting satellites, and being visible to the naked eye. The exact trajectory of the asteroid is not known, though the “hitting the earth” scenario has been all but ruled out (chance is less than 1 in 40,000).  Yet, with all measurement there is some uncertainty.  The gravitational pull of the sun, planets, other asteroids and even the solar wind can all alter the orbital mechanics.  So, with a massive object bearing down on earth we want to limit uncertainty as possible!  Being able to observe these events from earth is vital to our safety and well-being, as well as a source of excitement and wonder.  The sort of wonder that has encouraged thousands to pursue science for its benefit and for its beauty.

Apophis at 9:45 pm on Friday 5 March as seen from Christchurch, New Zealand. If your socks haven’t been blown off, you have failed the test to see if you still have the capacity of wonder and amazement. This is a 350m diameter ONLY rock some 16 MILLION kilometres away moving at 14,000 km/h! For the astronomer its magnitude was 15.9 (8.6 million times fainter than the brightest star) & it subtended an angle of 0.2 millionths of a degree.

Apophis’s shadow from a distant star passed over parts of the US on 22nd February and again on 7 March (from a different star: UPDATE – they were successful, see here).  These are called asteroid occultation events.  eVscope users were there to observe the event.  These citizen scientists are part of Unistellar’s Planetary Defence team (I’ll join as soon as a scheduled occultation occurs near Christchurch).  Their measurements of the very very subtle dimming of the star as the asteroid passes in front of it are automatically uploaded to SETI where the professionals work on the data to help define the orbit of Apophis and its shape more precisely.

Sadly, our views of the heavens are being shut out – shut out by the light pollution caused by excess lights, badly shielded lights, and high temperature LED light bulbs.  In Christchurch the city’s new street lighting has resulted in a huge increase in light pollution. Where once Matariki was easy to find, now it is possible only to the experienced amateur astronomer or the country dweller.  This need not be with only a little effort – all outside lighting must be limited, dim, well shielded pointing down to where the light only needs to be, and if it is LED light bulbs be 3000K or less (because the 4000K+ bluer light is more highly scattered as well as being damaging to insects and birds).  We can all participate in keeping our skies dark by turning off lights and insisting on dark sky friendly lighting.  For those more interested in the issues,  Blue Light Aotearoa from the Royal Society of New Zealand, and The International Dark Sky association are places to start.

Ps.  Some have ascribed the earthquake and tsunami to divine intervention because of bad press received earlier in the week.  “The God of Chaos” has messaged me to say he takes no responsibility.

*I have no financial interest in Unistellar beyond having backed the eVscope on Kickstarter.