We've decided to introduce a new, intermittent series to the Chandra blog. From time to time, we'll dig into our vast archive of questions submitted by the public and post the answers written by experts at the Chandra X-ray Center. Some of these will be Chandra-specific or at least X-ray astronomy related. Others, well, they'll be somewhat random. Enjoy.

Q:
I quote from http://chandra.harvard.edu/photo/2000/0170/index.html "The Roman numerals refer to how many electrons have been stripped from the atoms. e.g. OVIII is an ion that has lost 7 electrons from its atomic shell, NeX has lost 9 electrons, etc." This does not makesense. Do you mean OVIII has lost eight electrons and NeX has lost ten?

A:
Blame it on the Romans for not inventing zero. The neutral atoms, with zero electrons removed are labeled with I. For example HI for a neutral hydrogen atom, OI for a neutral oxygen atom, etc.

More Q&A in Resources: http://chandra.harvard.edu/resources/faq/


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Dark matter and light velocity

Now we know there's definite evidence there is something around us called dark matter, how do we know if some of the cosmological constants are not measured as they are because of the interference of dark matter itself? For instance, can we still assert the velocity of light is as it is in the "vacuum" when we found it is not vacuum, but dark matter? Can we assert with certainty the velocity of light outside dark matter medium? How? As it seems, it seems dark matter can be compared to Michelson and Morley's ether. Could it be the case the Special Relativity results to be poisoned by Dark Matter?

Wellington Lacerda
Brazil


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