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Comment by Stratoscope | Hacker News Reader

A star can't have have plutonium in its spectra. A single star doesn't have spectra, only a spectrum.

If you were talking about multiple stars, then yes, they would have spectra (the plural of spectrum).

To be clear, I don't mean this as a criticism of the submitter. :-) In fact, I appreciate that the title was changed from the original Wikipedia title to bring out the interesting part. Just wanted to note a little detail of spelling/grammar that is easily confused.

Plus, plutonium is only one of the interesting things about Przybylski's Star. It is a really weird star!

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I suspect we are confident that Pu is there because there are spectra indicating its presence, as opposed to a single spectrum.

Well, you may have me there. Now I am totally confused about whether it should be spectrum or spectra.

I suppose that means it's time for me to call it a night!

I think of in terms of the data we collect. Make a single measurement over a range of energies/wavelengths/frequencies and you have collected a spectrum. Repeat that measurement or make measurements covering different energies/wavelengths/frequencies and you have some spectra.

For the star from the article, I think it is fair to say that Pu consistently appears in the spectra that have been collected.

Thanks, that's an interesting way to look at it and makes complete sense to me.

At the risk of sounding like a total nitpicker, I am still a bit confused. I understand that you may measure the star's spectrum and get one result, and I may measure it and get a different result, so now we have two different (but hopefully fairly similar!) spectra for the star.

But does this mean that the star itself now has two different spectra? Or is it just that we've both measured it imperfectly and came out with different results?

As another example, suppose we have an object with a mass of exactly one gram. I measure it as 0.9999999 grams. You measure it as 1.0000001 grams.

Now we have two different masses for the object. Does that mean that the object itself now has two different masses (plural)? Or does it still has a single true mass of its own and we've both just suffered from experimental error?

I hope anyone reading this is not too annoyed - I'm just trying to understand how singular and plural work here, and to have some fun with the discussion. :-)

Scientists typically talk about measurements, observations, estimates, etc. Also, spectra of stars are in constant change, so it's not just experimental error.

> I'm just trying to understand how singular and plural work here, and to have some fun with the discussion.

Hey, that's my kind of discussion :)

There is no one "how singular and plural work here". Singular and plural inflections are a tool speakers can use to express a dimension of their thought; syntax isn't capable of fully determining which will appear.

Consider the sentence "my family are all Buddhists". "Family", the subject of the sentence, is unambiguously a singular noun, with plural form "families". The verb in the sentence is, also unambiguously, inflected for a plural subject. It's inflected that way because the speaker wishes, for purposes of the sentence, to conceive of their family as a collection of several people. In another context, it would be unsurprising to see "family" with singular verb agreement.

People may say "spectrum" or "spectra" based on what about the situation they're describing they want to provide focus on.

Many thanks to you as well as wycx, cperciva, and mirimir for engaging in the conversation. I learned a few things from you all!

I must confess: after my initial comment started gathering downvotes I was on the verge of deleting it. I'm glad I didn't, since it led to such an interesting and informative discussion.

I've seen this fairly often on HN, where someone posts a comment that is either factually wrong, off topic, or just something I strongly disagree with, and then a very interesting conversation follows from that. I make a point of upvoting the original comment along with the replies, since after all it was that comment that sparked the discussion.

The terminology is a bit confused. Astronomers speak of "a spectrum" where they mean "a measurement of a spectrum", and thus "spectra of a star" where they really mean "measurements (plural) of the spectrum (singular) of a star".

So it really comes down to whether you speak Latin or Astronomerese.

What was the title? It's been changed to Przybylski's Star now.

It was (I think I remember it right):

"A star with plutonium in its spectra"

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