Wednesday, February 20, 2008

What they don't tell you about tonight's total lunar eclipse

Is there any space news site or blog that has not had an article on the Total Lunar Eclipse from 3:01 to 3:51 UTC on Feb. 21 by now? They discuss it at NASA (even multi-lingual) and ESA, at Sky & Tel. and (earlier, still earlier), in the 'old media' (more, more, more, more, more, more, more, more, earlier, more) and the 'new media' (more, earlier, more, more, more, more, more). And yet none of these stories stresses what - in the opinion of this blogger who has observed numerous TLEs since 1975 - is really important:
  • The most impressive effect a total lunar eclipse causes can only be experienced when you are observing it from a site which has very little light pollution. It may feel odd to drive away from an urban location in bright full moon conditions, but you know why when partiality progresses: The darkening of the sky is nothing short of dramatic, then the Milky Way comes out, then it is brilliant - and somewhere in the sky there is this yellow, orange or red Moon-thing. You never get that all-sky beauty from an urban site! Call me crazy, but in this fundamental respect a TLE is somewhat comparable to a TSE ...

  • When observing the moon in eclipse, esp. in the (tonight 50) minutes of totality, do so repeatedly and perhaps make some notes: The pattern of colors on the lunar disk, caused by sunlight refracted into the Earth's umbra, sometimes changes minute by minute, in ways you may not expect. These patterns are not sharply defined, of course: Thus they are not seen best in a telescope with a magnification so high that the Moon fills your field of view. Rather observe them with low-power binoculars - or even your naked eye, if your vision's acuity permits. Photographing the changing color patterns is easy with modern digital cameras, even compact ones: As for the eye, high magnification is not necessary or even detrimental.

  • Finally, while total lunar eclipses are much more sedate sky shows than total (or annular) solar eclipses, they have their key moments that can be defined to the nearest minute or perhaps even second. This is actually a topic of current - though virtually unknown - research: How precisely can you time the onset and end of totality when the last penumbral light is vanishing or returning? This kind of observation with the naked eye has even some profound historical implications: If you could time totality to a minute or better you had a means to reset your ship's clock on the high seas, a potentially crucial step in getting your longitude right.
Much of what I just said are lessions from the last TLE which I could observe under perfect conditions in California or from its Saros predecessor which I - what a coincidence - also had the pleasure of seeing in dark conditions in another part of CA. Without that 1989 experience I might actually have never chosen a desert site for the 2007 TLE: If you've never seen an eclipse under these conditions you just don't know what you miss ... Talking about missing: Should you be clouded out (or in Asia or Oz where this TLE is invisible), there will be dozens of webcasts attempted, eg. here, here or here. There will also be a video broadcast - and a challenge for one lunar orbiter.

In other news rough seas could prevent the Navy from using the TLE time window for the first shot at USA 193: Already a third NOTAM for Saturday has been issued as have been maritime warnings for Feb. 21 to 25. A nice 3D graphic highlights the situation. The "shoot-down" of the satellite (again seen at -1 mag.) might leave a signal on IR weather pictures, by the way: Become your own space spook ...

1 comment:

cing said...

^^ nice blog!! ^@^

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