Rename Spectrum1D to Spectrum or SpectrumAligned or similar

[eteq]

From the Astropy 2023 Coordination meeting, a lot of people expressed that they thought there was a significant negative impact to specutils's use that people are confused that Spectrum1D doesn't actually mean what the "1D" seems to imply to people.

For background, https://specutils.readthedocs.io/en/stable/types_of_spectra.html#overview-of-how-specutils-represents-spectra explains the distinction, and clarifies how in Spectrum1D the "1D" really means that the spectral axis is 1D, but the flux can be any-dimensional. This is distinct from SpectrumCollection where both the spectral_axis and flux can be multidimensional.

But this name clearly trips up people - they see "spectrum 1d" and think that means the spectrum can only be 1D, and that it therefore misses their use case so they walk away. So this argues for renaming the class to something that doesn't give this impression.

What we did not come to was a clear answer to what the right name is (see item 2 of this bit of lore). Some ideas thrown out were to just have it be Spectrum ("drop the 1D. It's cleaner" - @nstarman). @WilliamJamieson suggested something like SpectrumAligned, which I don't love but don't know that I have an immediate suggestion. (@tepickering suggested SpectrumETEQ given a comment from me that "it's clear that the '1D' in Spectrum1D really only makes sense to me" 😉 )

cc @weaverba137 @WilliamJamieson @tepickering @nstarman @tomdonaldson @jehturner @pllim @taldcroft @perrygreenfield @larrybradley

[pllim]

If you are taking votes, Spectrum is less to type... so 👍 from me.

[nmearl]

I do like Spectrum.

An alternative might be to follow the NDData/CCDData approach and use SpectrumData. Or, numpy-esque with SpectrumArray, but that adds some ambiguity with SpectrumList.

[larrybradley]

I like Spectrum.

[rosteen]

Personally I like the simplicity of Spectrum, but I could also go for SpectrumData or even SpectralData.

[perrygreenfield]

I vote for Spectrum. I think the more general case where the spectrum may appear in multiple dimensions is the one that has the more complex name.

[nstarman]

And we could rename that one to Spectrums...

[pllim]

What about NDSpectrum like NDData? 😅

[rosteen]

It seems like the consensus is "Spectrum is fine", but GitHub can do polls now and I want to try the shiny new feature so I opened #1087 . Unfortunately it looks like you can only vote for one option, I would have preferred the ability to select multiple choices.

[aragilar]

Can we keep an alias around to avoid unnecessary code breakage?