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Take a look in the mirror. Now tell me the Earth has nothing to answer for. What a planet!
Indeed, what an amazing species the Earth has allowed us to become. The very nature of our orbit around the Sun, which happens to lie within the right zone—not too far and not too close—has, because we are situated precisely where we are, encouraged our sort of life. What would we be like if the Earth had been slightly closer to or further from the Sun? Or spun faster or slower? I mean it takes 243 Earth days for Venus to spin once—that's how long one Venusian day is. Would we have evolved as "us" under these circumstances? The Earth has allowed me to ask this question. But I could just as easily have asked, "What's for supper?" How great are we? We can flip from deep questions of existence to everyday ones in a moment.
Now, you may have informed ideas about life starting on a slightly different Earth, but ultimately there is no right or wrong answer. It's just like the "Do aliens exist?" question: No one knows for sure, so no one can be proved right or wrong, whatever arguments are put forward. Other questions can be answered with pure descriptions of what happens, but even these can still be pretty tricky. I always like "Why does the Moon look big close to the horizon, but smaller when higher up?", because it needs a bit of a run-up before you splat the answer in the questioner's face. For the first time, in Chapter g, I have tried to describe this phenomenon as clearly as possible, and it demonstrates perfectly the cunning nature of some seemingly innocent questions.
Let's have a look atthe Earth for some more examples of "Well, that's easy for you to ask" questions that need some serious attention when answering. Here's one: Why do we see different constellations at different times of year? Let's start the answer with another simple question: How long does it take the Earth to spin around once?
Twenty-four hours? We all know that the Earth spins once a day. Aha! Intriguingly there are two different kinds of day (actually there are several others, but they are really only for the serious wobble-and-tilt enthusiast). Why is this? It is because as well as the Earth spinning on its axis it is also orbiting the Sun. Which leads to two days of different lengths of time. Oh.
Our 24-hour-clock time is based on where the Sun is, and this is called the solar day (also as a synodic day—see the Astroglossary at the back of the book). However, the Earth actually spins around on its axis exactly once in a shorter 23 hours 6 minutes and 4 seconds—this is called the sidereal day, which is the time relative to the "fixed" distant stars. Forgetting the Sun, the sidereal day is one complete spin of the Earth.
Note the difference of nearly four minutes between the two days. Now, as far as I am aware, there is no name for this time difference. Yes, indeed, it's a problem for me. So I hereby name the four-minute time difference between the solar and sidereal days the Vamplew Time Shift (VTS). I've always wanted a time-unit thing, and now I have one.
To really understand this near four-minute shift, or rather the VTS, you could do a simple experiment. Stand up and pretend that you are the Earth. Be as real as you possibly can: wear blue (about 70 percent to represent the sea), white (for clouds, snow and big sheep), brown (deserts and brown things) and some green (trees and grass). Next you need a friend, preferably called Anna, to pretend to be the Sun—make sure she "shines" appropriately. To reproduce a day, start by facing each other a few yards apart. Anna, the Sun, stays still, while you spin around once counterclockwise (to the left) on the spot, coming back to face the Sun again. You have just done a day. Try it again if you're enjoying yourself.
Now, here's the thing: That isn't really how it happens. Turn around again, but this time move to the right as you turn. Remember to turn exactly once, that is a whole 360 degrees, but no more, and you have successfully represented the Sidereal Day. What should be apparent is that after your spin you are no longer facing Anna—she is off to the left a bit. Well, of course she is, you have stepped to the right. In order to face Anna again you must make an extra small counterclockwise turn. For the Earth, this little turn is that near four minutes' worth of spin. What you did by stepping to the right was to simulate the movement of the Earth in its orbit, ending up with that necessary extra bit of turn (the VTS) to get back to facing the Sun.
However, our lives are run by the Sun, clocks and everything, so what has the Sidereal Day really got to do with anything?
Well, not a lot with our daily lives, but as far as the constellations are concerned, this four-minute shift noticeably affects the night sky.
If I were to watch the constellation of Orion from Bad Goisern in Austria every day at exactly 7P.M., I would first catch a glimpse of the entire group in mid-December over in the east. The following day, it would have shifted slightly and would now be seen to be a little higher in the sky and a bit further south than the previous night. Its highest position, due south, would arrive at the end of February. After that, day by day, Orion moves down to the west and starts to disappear in the middle of May. Remember that I am charting Orion's position in the sky only from a fixed point in Austria at 7P.M. each day. But what applies to Orion applies to every constellation, and to the entire sky, wherever and whenever you are looking at it.Stargazing Secrets. Copyright � by Anton Vamplew. Reprinted by permission of HarperCollins Publishers, Inc. All rights reserved. Available now wherever books are sold.