Once upon a time there was a little asteroid that felt like it was missing something.
(Beware, I'm appealing to your dumb right brain - a sucker for stories, and anything dealing with emotion).
It had been a part of a larger body, called a planetesimal, but during the jostling of the early solar system this little chunk got knocked off and became an "asteroid."
It orbited the sun close in, with a good view of the inner planets Mercury, Venus and Earth. It wanted to get together with these big planets, as if to recover something of a lost destiny. (Your eyes are starting to feel wet, now).
It wandered, and it wandered, and little-by-little it managed to re-arrange its orbit to be close to all three inner planets. Sometimes it passed close to Mercury, sometimes Venus, and sometimes Earth. Of all these big planets, it like the Earth most. The Earth was blue, and it looked warm and inviting.
Because of the Earth's appeal to the little asteroid, it managed to adjust its orbit to get close to the Earth more often than to the other two planets. Other asteroids had done the same, and these "near Earth" asteroids became a family. They all liked the Earth, and came as close as possible as often as possible. Some of them came too close, but that's another story.
The little asteroid was not so little actually, for it was more than half a mile in diameter. Whenever a speck of dust went by, the asteroid would compliment itself on how big it was. It never saw anything bigger than itself, except for the three planets. It couldn't even remember the planetesimal it came from; it was such a traumatic experience.
Traumatic experiences sometimes await the unwary. Just as things have a beginning in a traumatic experience, they sometimes end that way. But that didn't enter the mind of the little asteroid. All it could think of was how nice it would be to get close to the Earth.
Orbit adjustment is a complicated matter. Sometimes the influence of one planet is undone by another. The complete story of this little asteroid cannot be told at this time. It will suffice to say that before its demise it made several beautiful close encounters with its beloved Earth. One of these most memorable encounters occurred in a year the Earthlings call 2001.
Unbeknownst to it, the little asteroid was seen by the Earthlings 3 years before this encoutner. They gave it the name "1998 WT24."
Now, an asteroid is a chunk of rock, and sometimes a collection of rocks with adhering stones and dust. The adhering force is gravity, and when nothing else is nearby the tiny force of gravity can accumulate over time to bring things together, and after many small encounters where things break it can collapse their orbits about each other and eventually hold them together. The little asteroid, being more than half a mile in diameter, weighed 4 billion tons! Since it was "floating" in space, it didn't weigh anything, but at least it had the mass of 4 billion tons. No wonder little asteroid thought of itself as big!
On this one, beautiful close pass by the Earth, in the Earthling Year of 2001, the 4 billion ton asteroid came closer to the Earth than on most past passes. It came as close as 1% of the distance that separates the Earth from the Sun. "How glorious I must look to the Earthlings!" the little asteroid declared - as its 4 billion tons of pride passed close to the Earth in the Earthling Year 2001.
Many Earthlings were taking pictures of the little asteroid dueing this pass. The time of closest approach was calculated to be the earthling day of December 16, on what the Earthlings call Universal Time. The Earthlings are funny with their terminology, for the Universe does not keep their time, or even know about it. Nevertheless, the Earthlings have a Universal Time, and all serious Earthlings use it. The unserious Earthlings use Local Time, and there are many local times. The one used in a place called California, a region smaller than Texas and less glorious than Texas, uses Pacific Standard Time. From California the little asteroid was visible at night (never visible in the day) on the night of December 15, Pacific Standard Time.
Here is the first picture taken of the little asteroid by one Earthling living in Santa Barbara, California.
Figure 1. Parts of constellations Auriga (left) and Perseus (right) are present in this 40 x 24 degree picture. Somewhere in this picture is the little asteroid, "WT." When viewed from 18 inches this photo covers a sky area similar to what you'd see with the naked eye. North is at the top, west to the right. [Nikon F3, 50 mm FL, f/3.7; 3.0 minute exposure, Fujicolor Superia X-tra 800; Santa Barbara, CA; 2001.12.16, 6:50 UT]
Well, in this picture it's a little difficult to see the 4 billion ton little asteroid, which would like to be called "WT." That's because the space beyond Earth is a big place. In this picture there are lines connecting stars that belong to something prehistoric Earthlings called "constellations." On the left is part of Auriga, and in the middle-right is most of a constellation called Perseus. Perseus is an ancient legendary hero who killed Medusa, a Gorgon whose appearance was enough to turn anyone unfortunate enough to look at her into stone. Let's not worry about the truth of any of this, for not many things the Earthlings believe in is really true.
"WT" is located near the middle of this picture. To locate it, we must first take a tour of Perseus. Start with the right-most star. The star to its left is slightly reddish, and is called Rho Persei. Above Rho Persei is Beta Persei, also called Algol. Algol is a famous variable star. It has a companion star that orbits in front of it every 3 days, causing it to dim to only 30% of its normal brightness when the companion orbits in front of it. Going up to the top, where three line segments meet, is the star Alpha Persei. Some ancients called this star "Mirfak" and said it marked the hero's elbow. I can't see it!
Continuing down the left side of Perseus we encounter Delta Persei, then Epsilon Persei. Halfway between these two stars, and to the right a little, is Nu Persei - not connected to any constellation lines. I'm going to call this star "A." The last three stars on the Perseus left side are Xi, Eta and Omicron Persei. Just above Xi Persei is the "California Nebula" - which is too faint to be seen in this picture.
In the next picture we're going to go closer to "WT"
Figure 2. This is a 2.4 times zoom-in of previous image, showing the middle part of Perseus. The image is 17.1 x 12.6 degrees. Stars "A" and "B" are connected to Epsilon Persei to form a triangle. [Nikon F3, 105 mm FL, f/4.5; 7.4 minute exposure, Fujicolor Superia X-tra 800; Santa Barbara, CA; 2001.12.16, 6:40 UT]
Little asteroid "WT" is inside the triangle. You can't see it in this image, because its 4 billion tons are so far away. We need to zoom-in closer to see it. That's what we'll do in the next picture.
Figure 3. Zooming in 3.4 times closer, to produce a 5.0 x 3.7 degree field of view, finally allows us to see a short streak below the "A" star produced by asteroid "WT." [Nikon F3, 400 mm FL, f/7; 10.2 minute exposure, Fujicolor Superia X-tra 800; Santa Barbara, CA; 2001.12.16, 6:30 UT]
Finally, we can see asteroid "WT" as it moves westward (to the right) in this 10.2-minute exposure. Let's get even closer, which happens in the next photo.
Figure 4. This is a 3.5 times closer zoom taken from the previous image, showing an area 1.44 x 1.06 degrees centered on asteroid "WT." The brightest star is magntiude 6.9, and the faintest are 14.0, which is 1600 times fainter than the naked eye can see. Asteroid "WT" is magnitude 9.7. The track is 10.6 'arc long (1/3 the apparent diameter of a full moon). [Nikon F3, 400 mm FL, f/7; 10.2 minute exposure, Fujicolor Superia X-tra 800; Santa Barbara, CA; 2001.12.16, 6:30 UT]
Figure 5. Here's a close-up of the asteroid's 10-minute track, which is 10.6 'arc long. This image corresponds to a zoom factor of 80 in relation to the naked eye view (of Fig. 1).
The width of the asteroid track in this image is about 5 "arc, which is the same as the stars - meaning that the real angular diameter of asteroid "WT" is smaller than I can measure from this photo.
Since "WT" is 1/2-mile in diameter, and at this time of closest approach it was a mere 1.2 million miles away, it should have an apparent diameter of 0.11 "arc, which is much smaller than I'm capbale of resolving. Asteroid "WT" is actually 50 times smaller than the width of the track in this image. Thus, the little asteroid is like a point of light, moving across a field of stars that are also points of light.
How tiny "WT" appears to us Earthlings! And how faint it is! We are misled by that big-sounding mass of 4 billion tons!
WT's view of the Earth during its closest approach must have been spectacular! The Earth was a big ball in the sky, about the same angular size as the Moon is for us. From its location just beyond the Earth, a mere 1% farther from the sun than Earth, "WT" would have seen a "New Earth" resembling our view of a New Moon. The main difference, thoug, is that the Earth was surrounded by a colorful halo due to atmospheric "forward scattering" of sunlight.
This Earth of ours is a wonderful place. No wonder "WT" wants to come close to us! Compared to Earth, "WT" is really just a miniscule pile of rocks. "WT" hardly warrants our notice!
But wait! Suppose "WT" succeeds in getting closer to us, and closer, until by a slight mistake it strikes us? Will it matter to us glorious Earthlings?
Consider what happened 65 million years ago, when "WT's" slightly bigger cousin collided with Earth?
This site opened: December 18, 2001. Last Update: December 18, 2001