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Log, Apr 30, 2004

15 people. It must be the end of April because all the URI Astronomy class students have arrived as they do almost every April. It was particularly heavy this year because we have had rainouts and other missing sessions this month. Not the sky was anything to rejoice about tonight.

First of all we had a Moon at 82% of full which made the sky hard to find second magnitude stars. Worse yet, until about 10:30 there was a thin layer of clouds which were very bright. At times even the brilliant stalwarts of Jupiter and Venus were only relatively dim.

We tried to spot Comet Neat by eye. For a moment we were hopeful when we saw a clear commentary tail leading to a bright nucleus, but a moment later we recognized the "nucleus". It was a few orders of magnitude heavier than any nucleus yet discovered. It was a solar system denizen however. Alas it was only Mars strategically placed in a cloud wisp that made it look like a comet.

We looked at bright objects all night. In fact, the haze actually made the sky very stable and we go rather good views of Jupiter. We could pick out a couple of dark spots on Jupiter's surface that Les wondered if one of them could be the shadow of Europa which at this time was crossing the face of Jupiter. Joe dashed this idea by explaining that BOTH were turning during the course of the evening in lock step. All we were seeing was dark whorls in the northern dark band.

Saturn presented a very crisp image but only a few of its moons could be picked out in the very bright sky. We had many people look at the Moon through our polarizing filter to cut down on the glare. We pointed out the central ejecta mass of many of the large circular craters.

Venus was very brilliant and a surprise to many people as it was both very bright and just a relatively thin crescent. This apparent contradiction (thin crescent but large brightness) is explained by the fact that Venus is very close to Earth currently and is apparently much larger than we usually see. In fact as Venus passes close to us, it is more than seven times as large across as when it is full (and on the far side of the solar system).

Venus will be passing in front of the Sun on June 8th for the first time since the nineteenth century. Because Venus' orbit is tilted at about 3.5 degrees to the Earth's orbit, Venus usually passes above or below the Sun which is only 0.5 degrees across. Only when Venus, the Sun and Earth all line up approximately at the point where the orbits of Venus and the Earth cross (the so called line of nodes), is there a chance to see Venus cross the face of the Sun. On average this only happens twice every 122 years and then these pairs occur 8 years apart. We will get a shot at dawn to watch Venus in the act (already underway at dawn) on June 8th and again in 2012 when we have a better chance to see the whole show. Folks in Europe, western Asia and will get to see all or most of the show. Folks on the west coast of the Americas and the Pacific islanders will miss nearly everything.

We have been asked whether Frosty Drew plans to do anything for this sighting. The answer is that we really are not set up to do anything. Our Observatory does not include safe solar shields for the large 16" telescope. Looking at the Sun through a 16" telescope without proper filters will blind the viewer. In fact, looking at the Sun through a mirror this big will actually burn through the eye into the brain if the viewer manages to spend more than a few moments in the focus. While several members have private telescopes equipped to view the Sun (and so the Venus Transit) we will not be open for the general public.

Since in general viewing the Sun is not safe, FDO will not expose the public to this potential hazard even though it can be made safe. Explaining to young children that dark shields in front of telescopes do NOT MEAN that putting on sunglasses to look at the Sun through binoculars is simply unwarranted. A high school teacher in South Carolina was prosecuted after he had his class use glass filters fogged with candle soot as "safe filters". He blinded 15 teens in one or both eyes permanently in the 1990s.

If you attempt to view Venus in transit, please remember to take all the precautions you would normally take for a solar eclipse. If you use an optical system, make sure you either have approved shields, or use eyepiece projection. Remember that it you do not use shields in front of the primary objective (the big lens or the big mirror which first sees the Sun's light), that the insides of the telescope will get very hot. It is quite possible to melt eyepieces even if the temperature gets nowhere close to the melting point of glass because the spaces between the lenses of the eyepiece use organic materials such as clarified pine resin or plastics. You may very well destroy an eyepiece or even an entire telescope if you allow more than a momentary pointing at the Sun. At least, destroying a telescope is better than destroying your vision. It can happen if you look at the Sun for an extended period.

-Les Coleman

Leslie Coleman
Author:
Leslie Coleman
Entry Date:
Apr 30, 2004
Published Under:
Leslie Coleman's Log
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