An asteroid discovered earlier this year will make its closest approach to Earth today, coincidentally just as the planet is experiencing equal parts day and night. There is no danger of a collision – 2021 NY1 will never get closer than the Moon – but the event reminds us the Solar System is a dangerous place, and we don't know everything that is out there.
2021 NY1 is between 130 and 300 meters (420-990 feet) long, making it somewhere between the height of a 30 and 80 story building. At that size, it is no dinosaur killer, but it could do some serious local damage if it hit the planet. It's almost certainly larger, for example, than the object this week proposed to have exploded over the Dead Sea, potentially inspiring the Biblical story of the destruction of Sodom and Gomorrah.
There's no need for us to watch out for fire and brimstone from the skies in this case, though. 2021 NY1's close approaches have been mapped out up to 2192 and none of them are terribly close. In fact, at 2:41 pm UTC today it will be at the closest it's going to get to us over that entire period, when it will be just over 1 percent of the distance from the Earth to the Sun away, or 1.5 million kilometers (932,000 miles), four times the distance to the Moon.
The next time 2021 NY1 will get close at all will be 2044, and it will then be almost four times further away than today, although it will be almost this close in 2105 if anyone expects to be around to see it.
2021 NY1 has an orbit that takes it out to well past Mars, almost 2.5 times as far from the Sun as the Earth ever gets. More importantly from our perspective, its closest approach to the Sun is 1 percent inside the Earth's orbit.
Near-Earth Objects (NEOs) like this one make moderately close approaches quite frequently. It's just a month since a considerably larger one went past at around twice the distance. However, in that case, we had known about it for five years before.
As the name suggests, 2021 NY1 was only discovered this year, in June as it happens. It's another reminder there are a lot of NEOs out there we don't know about, and if one is heading our way we might not get much warning.
One way 2021 NY1 stands out from other asteroids is that its close approach coincides with the equinox, when both hemispheres have 12 hours of day and night no matter how far you are from the equator. Technically the exact moment of the (Northern Hemisphere) autumnal equinox this year is September 22 at 3:20 pm EDT (7:20 pm UTC), so the asteroid visit is about five hours early.