tj@alliant.UUCP (Tom Jaskiewicz) (10/16/86)
In article <649@nike.UUCP> watson@nike.UUCP (John S. Watson) writes: > Is it possible to have a sunset eclipse? >Or is the geometry such that it can only happen during mid-day, Both sunrise and sunset eclipses do occur. An eclipse is the shadow of the moon crossing the surface of the earth. The path of totality usually begins at sunrise and ends at sunset. > Or is it that eclipses are so >rare that a sunset eclipse has just never happened in recorded memory? People who go to see or study solar eclipses usually want the longest possible period of totality, which occurs around noon. Not many try to see the sunrise or sunset eclipse. The 1984 total solar eclipse had only 1 landfall (both the sunrise and sunset eclipses were at sea). You had to get up early to see the partial phase at sunrise and the total phase an hour later. But the people who did this would have preferred to be a a point closer to midday. The only such point was aboard a ship, which isn't good for telescopes and other equipment. Quiz time: You are planning to be on a beach to see an eclipse at sunset. How much sandy space will be available to set up telescopes in? That is, will the tide be low or high (or in between)? -- #################################################################### # uucp: decvax!linus!alliant!tj ## Bernese are mountains of love. # ####################################################################
palmer@cit-vax.Caltech.Edu (David Palmer) (10/20/86)
Organization : California Institute of Technology
The danger of looking at a partially eclipsed sun is much greater than
that of looking at an uneclipsed sun.
When the sun is partially eclipsed, it produces less light (obviously)
which makes your surroundings darker. To compensate, your eyes open up from
an iris diameter of about 1mm to a diameter of about 7mm, a fifty-fold
increase.
Then, when you look at the sun, the image you see has a much greater
intensity (light per unit area on the retina) than it would have if your eyes
were stopped down and you looked at an uneclipsed sun. (The iris has adjusted
so that the same total amount of light comes through, but since the area
producing that light has been decreased, the intensity has increased.)
This high intensity light can damage the retina much more quickly
than an ordinary glance at the sun can.
Another point, someone mentioned that they had used two slides made
from unexposed film as a sun filter. I have heard that THIS IS A VERY BAD IDEA.
Apparently, color film, when exposed and developed, only blocks out the
visible light, letting IR and UV through. Probably the same is true of
exposed and developed color slide film. You should only use exposed and
developed black and white film, which apparently, does not have this problem,
although it may have others. (Use at least two layers, and, just in case,
only use one eye. Monocular vision is better than none)
David Palmer
palmer@cit-vax.edu
...seismo!cit-vax!palmer
I've followed you, talked to your neighbours, tapped your phone,
and even shot at you to see how you would react. From my observations
I have come to one irrefutable conclusion: You are Paranoid.sarah@prism.UUCP (10/20/86)
is it an eclipse of the sun or moon? if moon (in the east) it will be high tide if sun (in the west) it will be low tide
biagioni@unc.UUCP (Edoardo Biagioni) (10/21/86)
In article <331@alliant.UUCP> tj@alliant.UUCP (Tom Jaskiewicz) writes: >Quiz time: You are planning to be on a beach to see an eclipse at > sunset. How much sandy space will be available to set > up telescopes in? That is, will the tide be low or > high (or in between)? >#################################################################### ># uucp: decvax!linus!alliant!tj ## Bernese are mountains of love. # >#################################################################### You will have a conjunction low tide ==> lots of space. The moon and sun are both 90 degrees from overhead, attracting the ocean's water to places a quarter of the way around the world from you. That means a lot of water is elsewhere, i.e., you have low tide. Ed Biagioni decvax!mcnc!unc!john!biagioni seismo!mcnc!unc!john!biagioni
evp@lewey.UUCP (Ed Post) (10/24/86)
[Question whether high or low tides accompany a sunset eclipse.] > is it an eclipse of the sun or moon? > if moon (in the east) it will be high tide > if sun (in the west) it will be low tide This question was somewhat underspecified. Of course, in the best of all possible worlds it would be a low tide -- two bulges of water (one directly under the moon, one exactly opposite) are created as the result of tidal forces. This was all discussed weeks ago in this newsgroup. However, the tides at any one location can lead or lag the theoretical time by several hours because of resonance effects in oceans and large bays. In practice, without a detailed understanding of the tidal patterns at the location in question, you have very little chance of getting an accurate answer. -- Ed Post {hplabs,voder,pyramid}!lewey!evp American Information Technology 10201 Torre Ave. Cupertino CA 95014 (408)252-8713