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Do not do either of these.

A floppy disk has only marginal IR protection, and blurs the image heavily.

Soot works if you deposit it at the right thickness, but it's easy to get the thickness wrong, and the slightest smudge can eliminate your protection; the coating is very fragile.

A common third trick is looking through CDs. Which can work, if you pick the right one, but their transparency varies dramatically, so there's no guarantee that an arbitrary one will offer sufficient protection. If you're willing to risk your eyes with an improvised filter, a CD should be good if you can barely see an incandescent bulb through it.

Photography filters and photographic film should never be used for looking at the sun. They don't block nearly enough IR.

More info about various homemade and professional filters tested here.

From the link in my other post (again, ), we see that the main problem with CDs is not a fundamental aspect of using them, but simply that their overall transmittance varies depending on how thick the metalized coating is, which can be assessed in advance by looking at the filament of an incandescent bulb. Beyond that, their stats seem to be impressive. The standard recommendation for looking at the sun is #14 welding filter, which is way out of the range for potential eye damage. For a CD or stack of CDs with equivalent visible light attenuation, the UVA level is 2.5x the welding filter and the UVB level is approximately the same - easily in the safe range. The CD actually slightly outperforms the welding filter in IR blocking.

Finally, no more having to rely on flat assertions about "everything but welders glass and eclipse filters is dangerous for you!"

Link

The summary section:

Not surprisingly, there was a wide range in the attenuation of visible light by these filter materials. Even among the "safe" filters, there was considerable variation in transmission levels. For example, the differences in processing methods and chemistry resulted in considerable variation in optical density of the silver-bearing black-and-white film emulsions. The double-layer filters had shade numbers between 11 and 16.

I have recently also found a wide range of optical density between individual audio and data compact disks (CD and CD-ROM) because of variations in manufacturing processes. Some compact disks have aluminum films which are so thin that they appear semi-transparent at normal room illumination levels. These CDs are unsuitable for use as solar filters. Higher quality CDs are suitable for use if the aluminum coating is dense enough that the glowing filament of an incandescent light bulb is just barely visible through it.

Floppy disk media have a marginally safe infrared transmission, and produce poor quality images of the solar disk. The magnetic media scatters visible light to the extent that one sees a dull red disk surrounded by a broad halo of red light. I would not recommend using this material for a solar filter.

The most consistent performance was found with the polyester and glass filters. I would avoid aluminized polyester which is used in wrappers for food products and collector cards because of the inconsistent optical quality, but even my sample of Poptarts wrapper performed surprisingly well in terms of protection from optical radiation. (It rated as marginally safe.) However, most of the filter materials specifically designed for eye protection easily met all of the transmittance criteria for safe filters.

Unsafe filters include any image-bearing photographic emulsion, chromogenic (non-silver-bearing) black-and-white film, black processed color film, photographic neutral density filters and polarizing filters. Although these materials have very low luminous transmittance levels, they transmit an unacceptably high level of near-infrared radiation. The black color film is a good example, having a shade number of 15 for visible light, but transmitting almost 50% of the infrared radiation!

Infrared transmittance levels shown in Table 2 should be regarded as the upper limit of transmittance in the waveband 780 to 1400 nm. The signal-to-noise ratio for low-level measurements in this waveband is extremely low, and thus these data are less reliable than those in the shorter wavebands. Note that even some glass filters with very good safety performance histories such as the Questar and Thousand Oaks glass filters showed infrared transmission levels up to 0.4%.

Smoked glass had very good performance in terms of transmission of visible light and infrared radiation. However, it is a dangerous filter material for two reasons. First, it is very difficult to produce a heavy uniform coating of soot on glass. Second, the coating is very fragile. It is very easy to destroy the filter by handling it. Much of the soot on my sample came off because of contact with its protective wrapping. It also made quite a mess.

There you go :)

if it's during a lunar eclipse, then the sun is between the earth and the moon, so it's closer.

In a lunar eclipse, the Earth is between the moon and the Sun. http://www.mreclipse.com/Special/LEprimer.html http://en.wikipedia.org/wiki/Lunar_eclipse

You can prove the Earth is round by looking at a lunar eclipse.

I'm not quite sure this is true. First you have to assume that it's actually the Earth's shadow. Then you have to assume that you aren't simply seeing the shadow of the flat, round Earth when the Sun is directly behind it, which is exactly what happens during a lunar eclipse.

The eclipse lasts over 3 hours (8:43pm to 12:09am). It's totality, when the moon passes through the umbra (i.e. the core of the shadow as the summary quotes), that lasts for an hour lasts from 10pm to 11pm. More info on lunar eclipses at http://www.mreclipse.com/Special/LEprimer.html

Before Einstein explained the precession of Mercury's perihelion, many scientists believed there was a planet Vulcan inside Mercury's orbit. Some even "spotted" it.

(For the "spotted" link, search on "Vulcan".)

You can also read about it here.

Before Einstein explained the precession of Mercury's perihelion, many scientists believed there was a planet Vulcan inside Mercury's orbit. Some even "spotted" it. (For the "Some" link, search on "Vulcan".)

I submitted the story this morning and was rejected. I think Starry Skies did just as good a job if not better of covering the eclipse than space.com. I did the html for Kathy, and find it interesting that while Kathy is disabled and we did the pages with a budget of zero - I think she did a mighty fine job. I would have liked to see what we could have done if we had the resources of space.com, who have paid writers and staff. Furthermore the guy running the NASA eclipse site and Mr Eclipse has asked Kathy for permission to use her Columbus article on those sites.

Here is what I submitted early this morning, I certainly thought it was worthy of the top page of slashdot... Take a look and let us know what you thing.

Total Lunar Eclipse Tonight

The May 15/16 lunar eclipse starts at 9:05 p.m. EDT and will be visible over North and South America as well as western Europe and Africa. Eastern US and Canada will be able to see the entire eclipse. In the western US and Canada, the partial phase of the eclipse begins before the Moon rises and for the Pacific northwest, the Moon will rise while in totality. For times in your area, folklore, an interesting story on the Lunar Eclipse that Saved Christopher Columbus, and more see The StarrySkies Lunar Eclipse Pages.

One of my favorites shows the 1970 eclipse near total, with a diamond-ring effect". I actually saw that one--it was amazing. When the sky gets dark, the birds figure it's night and go roost in the trees. Beautiful.

Mr. Eclipse also links to Ceduna info, including an animation of the shadow's path across earth.

One of my favorites shows the 1970 eclipse near total, with a diamond-ring effect". I actually saw that one--it was amazing. When the sky gets dark, the birds figure it's night and go roost in the trees. Beautiful.

Mr. Eclipse also links to Ceduna info, including an animation of the shadow's path across earth.

How about learning some Geography? ;-) Austria != Australia.

As your map shows, there was a total solar eclipse on Aug 11 1999 passing through Austria (Europe!).

See also here, here for photos, and here for more reports.