Let’s pretend we’re still in June, for two reasons: because we wish we weren’t already into the latter half of yet another year (and the month of my birthday), and because the last day of June was Asteroid Day.
I failed to celebrate it because what I tried to put together about the asteroids had problems, after much work. But here’s something about the event of 112 years ago, which Asteroid Day commemorates.
In this picture, the streak for the Tunguska object is guessed, not calculated.
On 1908 June 30, at about 7:17 by local Siberian time, the native people (Buryat, Evenki, and others) and Russian settlers of a thinly populated region northwest of Lake Baikal saw the sky split by a long bluish flash almost as bright as the low morning Sun, followed by noise like artillery, then shock waves that knocked them off their feet and that reached, hours later, as far as Britain in one direction and Washington D.C. in the other. The trees of the taiga forest were flattened radially outward over an area of nearly a thousand square miles.
There is no town nearby; the event got its name from the Podkamennaya Tunguska, Stony Tunguska river, which got its name from the Tungusic-speaking peoples of the region, and which like the Nizhnya Tunguska, Lower Tunguska, joins the great Yenisei to flow into the Arctic Ocean.
Not till 13 years later did scientists get to the remote region and gather evidence of what had happened, so there is much uncertainty. Was it a comet, a small asteroid, even a black hole passing through the Earth? Calculations are that an object maybe 50 meters wide exploded maybe 100 kilometers up in the atmosphere. Though no parts of it and no crater have been found on the ground, it counts as the largest impact in recorded history – not as large as the unrecorded strikes that caused Meteor Crater or, millions of years ago, the Chicxulub buried crater and the end of the Cretaceous age.
Plausibly, though not certainly, it was a fragment of 2P Encke, the periodic comet that, because of the shortness of its orbit, returns most frequently – every 3.3 years since its first discovery in 1786. Johann Encke was not one of its independent discoverers, but was the mathematician who in 1819 by laborious calculations proved that several previous comets were the same one.
The Beta Taurid meteor shower peaks on June 28 or 29; it is caused by one of the debris streams from that comet, and is a daylight shower, detected by radar, because it is in the out-going part of the orbit and therefore, like the Tunguska object, hits the sunward side of Earth. The shower’s radiant is near the star Zeta Tauri, the tip of the Bull’s southern horn, which at the end of June is not far south and west of the Sun.
Lines on the ecliptic place are 1 astronomical unit (Sun-Earth distance) apart. The thicker line is the vernal equinox direction. The comet’s path is shown for 2020. Stalks from it to the ecliptic plane are at 1-month intervals.
We are now passing over Encke’s orbit, but the comet itself is some way back along the orbit, having passed through its perihelion – closest point to the Sun – on June 25. It was then at its brightest, perhaps up to a naked-eye magnitude 5, but was only 15° from the Sun. We are now coming into a time that is more favorable, though not perfect. Encke’s comet may still be at, or not far below, the naked-eye level, and is farther out into the evening sky, though sinking southward. That’s the nature of this tantalizing comet’s orbit.
Because it is near, it speeds across the sky, and I have to show its path in two pieces.
<I>See the end note about enlarging illustrations. In these charts. the comet’s possible dust tail, pushed away from the Sun, is indicated schematically.
We will pass nearest to the comet on July 29, but, receding from the Sun, it will have dimmed past magnitude 9, and will have become 34° more southerly than the Sun.
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Thank you Guy. This is the clearest and most sober discussion of the Tunguska event I have ever read. The illustration of the possible course of the asteroid at impact is enlightening, and the possible connection to Comet Encke makes a lot of sense.
I’m underwhelmed by “Asteroid Day” and all the hoopla about defending Earth from asteroid and comet impacts. Sooner or later another big chunk of rock or ice will hit the Earth and cause havoc. A catastrophic impact is highly unlikely during the lifetime of anyone alive today. We can’t do anything about it currently, and all the proposed defenses are unlikely to be highly effective, even if we developed them in time. In the mean time, there are numerous other threats to life on planet Earth that are happening right now and which we could respond to with great effect, if we muster the political and economic will. Global heating and climate change is the most glaringly obvious problem. I think we should focus our energies on things that are killing us right now and which we can do something about, and just hope and pray that nothing big hits us from outer space.
And if an asteroid hadn’t wiped out the dinosaurs, all of us mammals might have remained tiny insectivorous tree-dwelling quadrupeds. Sometimes change is good.
I think that Tunguska was only investigated in around 1928 when Stalin sent scientists to look around and they returned some valuable information about it but inconclusive as to the cause.all kinds of theories;anti matter,an exploding UFO(although that might merge with anti matter if it had an anti matter drive?),a comet,a meteors.im going with an air burst of part of a comet or meteor since I have concluded that UFOs don’t come here from other planets and if genuine they are related to whatever phenomena produces ghosts and the like and are therefore a phenomena of the mind rather than the physical world although the obvious problem occurs where do you draw the line?
I can see how a chunk of the comet could have been the Tunguska object. The comet was fairly close to the Earth on its current go around, passing over our orbit in early August according to your diagram. If the comet crosses our orbit every 3 years and 4 months, it should cross Earth’s orbit again in December of 2023, then in April 2027, then another close passage (to Earth) in August of 2030.
Wikipedia says its minimum orbital intersection distance is .17 A.U., and it will pass at that distance on 2172 June 29. Wikipedia also states that the orbits of comets are altered due to gravitational perturbations and outgassing, which tells me it may strike the Earth again. I think you refer to outgassing as non-gravitational effects on a comet’s orbit.
Encke’s orbit has been remarkably stable; the period has been found to be 3.30 years at discovery and at most returns, occasionally becoming slightly shorter and then returning to 3.30. I assume this is because it does not go out as far the orbit of Jupiter; passages near to Jupiter are the common cause of deflection of comets’ orbits.
Meteors have typically separated from their comets centuries before we see them, so perhaps the Tunguska chunk did.
Alastair McBeath, who answered some questions of mine about the Tunguska object, may correct me.