Five large asteroids skimmed Earth yesterday. The closest, asteroid 2019-OK, just discovered in the last 36 hours is 250 feet wide and missed us by just 45,000 miles, 0.2 the distance to the Moon. This early evening Arizona time it will have reached magnitude 9.4, which I can spot with my high powered binoculars. A thee inch telescope would work also to see it. Unfortunately, it is poorly timed and placed to observe before it fades. Please note that it is moving very quickly and seven hours later the magnitude has dropped to an impossible +46 as most of the dark side faces Earth, about as bright as a pen light sitting on the Moon. Not even Hubble would have a good shot at that.
An impact of an object that size would have made a crater about 1.25 miles across and wiped out most life in an area the size of Connecticut. At that distance 1/144 objects will impact the Earth. For objects that come closer than the Moon the impact ratio is 1/3600.
Asteroid 2019-OD, discovered a few weeks ago, came 0.9 lunar distance from Earth today. It is almost identical in size at 237 feet wide. It was best visible last evening in the southern hemisphere at magnitude 12.79, 6 inch telescope range.
Asteroid 2015-HM10, discovered 4 years ago also is nearly the same size at 225 feet wide, but safely missed us by 12.2 lunar distance, about 2.9 million miles. Asteroid 2019-OE, at 2.5 lunar distance about 600,000 miles away, is 100 feet across. An impact from this one would be much larger than Chelyabinsk, but smaller than Meteor Crater. Both of these asteroids would have been too dim to be seen at magnitude +17.5.
Heads up. You can learn about and see some of the larger Near Earth Asteroids NEO's which pass closer than 20 LD at http://www.spaceweather.com/ Click the Ephemeris tab, enter your home observing coordinates, date, and duration to generate where they may be seen in the sky.
Tomorrow, the even bigger Asteroid 2010-PK9 at 500+ feet will miss us by 8.2 LD. Asteroid 2010-PK9 is a rare Aten class asteroid whose orbit brings it much closer to the Sun. In this case half as close as Mercury in a 205 day highly elliptical orbit. About two dozen more NEO's are listed in the next couple of months with more discovered and updated daily.
You realize that only about 10%~ of these relatively small and very close NEO's are even observed as they pass by
