Friday, 26th May 2017

«

»

Feb 28 2008

The Total Lunar Eclipse of February 21, 2008

IMG_0619_cr_lb2

On February 21, 2008 a total lunar eclipse took place, almost a year after that of March 3-4, 2007. The viewing conditions, however, were much more favorable for the Americas, as it was to occur around midnight. Consequently, this eclipse was fully observable only in the westernmost part of Europe, very late at night. (Note: all times in this article are Central European Time, also known as CET = GMT + 1h).

 

 

Map for the total lunar eclipse of February 21, 2008. (C) F. Espenak, NASA/GSFC .

LE2008Feb21T2

Observing location and setup

In addition to the not-so-handy observing conditions, the weather prospects around the time of the eclipse were really lousy. Even the previous afternoon, all numerical weather prediction models left little to no hope to even have a peek at the eclipse, as the sky was expected to be uniformly overcast over most of Italy. I had originally planned to watch and image the eclipse together with a bunch of friends (it’s way more fun than being alone!), but due to the poor weather forecast, I resolved to stay home and watch it from there. Atfer all, I do have a nice balcony with the right orientation, and in case of bad weather, all I had to do was just to slump back in my bed and fall asleep :-D

Here’s my setup for imaging the eclipse:

  • Canon EOS 300D (aka Digital Rebel) DSLR camera @ 400 ISO
  • Scope: Vixen ED103SWT (Aperture: 103mm, focal length: 795 mm)
  • Losmandy G11 equatorial mount with FS-2 motor drive
  • A laptop
  • Software: DSLRFocus for camera remote control
  • Other accessories

Here’s my rig, ready for action:

P1000117

Actually, the laptop in the picture was just a last-minute makeshift, with a very quick and dirty installation. Unfortunately, my good ol’ Asus laptop kicked the bucket just a while ago, after more than four year’s service. Its successor (an entry-level Sony Vaio) came with Windows Vista, which supports neither the Canon EOS 300D (i.e. no driver available) nor many astronomical imaging programs I normally use. Needless to say, instead of going to bed I spent the first part of the night setting my laptop up! :’(

The eclipse

Everybody knows that accurate weather forecasting is no easy task, mainly because the Earth’s atmosphere is a highly caotic and unpredictable system, of which our understanding (and consequently, our mathematical models) is quite poor as compared to, say, celestial mechanics. So it can happen that the meteo guys may be wrong, which is something you wouldn’t want to happen . But there are a few exceptions to this rule, namely when the weather turns out to be good. This was the case here, as in the evening of Feb. 20 the sky cleared up, a real godsend. At least that’s what happened on northwestern Lombardy (NW of Milan). Most of Italy, however, was clouded out, including my hometown (Genova) :-D

Since I hadn’t had enough time to fully automatize the image acquisition procedure, I “just” took 180 pictures, between 2.45 am and 6.01 am. I typically shot three exposures every five minutes, one being taken according to the standard exposure tables, and the other two making a two-stop bracket. During the totality phase, I actually took more pictures.

To start off, let’s have a look at a five-exposure composite made with Photoshop, which is meant to show the size of Earth’s umbra with respect to the Moon’s. Here are the technical specs for the five pictures:

  1. 03:21 CET, 1/400s
  2. 04:04 CET, 2s (a few minutes after the start of totality)
  3. 04:24 CET, 4s (around mid-eclipse)
  4. 04:52 CET, 2s (end of totality)
  5. 05:31 CET, 1/320s
composite1

Below is a different version, highlighting Moon’s path (white line) and Earth’s umbra (yellow circle):

composite2

In comparison with 2007′s total lunar eclipse, it is worth noting that this time the Moon passed “below” the ecliptic, that is, in the “lower” half of Earth’s umbra (in terms of heliocentrical ecliptical coordinates, this implies Z < 0), while last year the Moon raced through the “upper” part (i.e. with Z > 0).

Here’s a shot taken around the start of totality (03:58 CET, 4s exp.):

img_0619_cr_lb2

Finally, here’s a mosaic from 20 exposures between 02:47 am and 06:01 am. In the last two images our satellite was partially covered by a cloud bank:

mosaic

Last but not least…

Of course, Mr. Murphy never misses a chance to screw something up. After focusing carefully on a star (FWHM value of an unsaturated star with DSLRFocus), I also duly tightened all screws, including the two responsibile for holding the camera and the 2-inch to T2 adapter ring. Much to my chagrin, as soon as the eclipse was over I started packing up, and when I pointed my flashlight at the telescope I found out that one of the two focuser setscrews had loosened, thereby throwing the focus off for half of the whole eclipse :’( . Needless to say, it is highest on my priority list to change my scope’s crappy focuser with one more up to par with its optical quality!

All in all, it was well worth an all-nighter, given the poor weather prospects. And don’t forget: it won’t be until 2010 that we’ll be able to see another lunar eclipse.

This post is also available in: Italian