Editing 1733: Solar Spectrum

{{comic
| number    = 1733
| date      = September 15, 2016
| title     = Solar Spectrum
| image     = solar_spectrum.png
| titletext = I still don't understand why the Sun paid the extra money for Transitions lenses.
}}

==Explanation==
This comic's release day was postponed from the scheduled Wednesday release to a [[:Category:Thursday comics|Thursday release]] because [[Randall]] noticed the extreme popularity of the previous comic on Monday: [[1732: Earth Temperature Timeline]]. Randall even explained this in the header text; see [[1732#Popularity_of_comic|this trivia item]] from the previous comic.

This comic depicts the {{w|Fraunhofer lines}}, i.e. the {{w|spectral lines}} seen when sunlight is split in a {{w|spectrometer}}. These appear as black gaps in the rainbow of light, caused by light being absorbed by {{w|Chemical element|elements}} in the {{w|Sun}}. The frequencies of light that an atom absorbs depend on the exact arrangement of electron orbitals around it - because each element has a different pattern of orbitals, each one has a distinctive pattern in the absorption spectrum. The chart shows most of the main lines in the visible spectrum and identifies the elements linked to them. 

The image of the Fraunhofer lines from Wikipedia is shown below in the section with a [[#Table of spectrum|table]] of these lines. Here it can be seen that all the lines that are labeled with elements are correctly labeled. Also all lines shown in the part of the spectrum included in the comic are included. Ten of the lines included are not labeled in the picture on Wikipedia (at least not with an element; two of the three "h" labels are not in the table on Wikipedia). Six of these also have no label in the comic. The other four lines' label ''Those giant sunglasses'' constitutes the joke of the comic. There seems to be only one clear error in the comic and that is the fifth line labeled Sunglasses, the middle of the lines, which is actually a Hydrogen line (C in the picture below). But the line next to it to the right is one of those not labeled in either picture and it seems likely that it was this line Randall meant to be a Sunglass line...

All ten extra lines (including both the labeled and unlabeled ones) seem to correspond to the [http://astro.u-strasbg.fr/~koppen/discharge/silicon.jpg spectrum of silicon], and '''the joke then refers to the {{w|silicon dioxide}} (aka glass)''' used in the lenses of the Sun's sunglasses. Of course, this means that the glasses have been ionized and turned into plasma by the heat of the sun. 

The idea of a sun with sunglasses is a reference to pictures/clipart of the sun wearing sunglasses, often used to denote good weather. Randall has specifically used this picture in at least two ''[[what if? (blog)|what if?]]'' articles:
:In ''{{what if|115|Into the Sun}}'' it is seen in the fourth image. The title text of that image even references the fact that those sunglasses will block the light to Earth:
::A partial solar eclipse is when the Earth moves across the part of the Sun blocked by its sunglasses.
So this comic is a direct callback to this what if? post.
:In ''{{what if|129|Black Hole Moon}}'' it is in the first image also including a banana as the mouth. Both the image and the title text of that image references the fact that those sunglasses will block (eclipse) some the light to Earth:
::Doctors warn that even sunglasses that block UVB will only protect you from the part of the Sun covered by them.

There is another joke in drawing a sun with sunglasses because sunglasses are meant to protect your eyes from the sun, so what should they protect the Sun's eye from, Star light...? Also, any glasses worn by the sun, would they not become sun glasses?

{{w|Transitions Optical|Transitions}}&reg; is a brand of {{w|Photochromic lens|photochromic lenses}}; however, photochromic lenses are often referred to as "transition lenses", so the title text does not necessarily refer to the brand. Photochromic lenses are a type of plastic lens used in prescription spectacles that allow the lens to turn dark when exposed to UV light such as that found in sunlight. The sun choosing to get transition lens would prove a waste of money as the lenses would be permanently transitioned to be dark, so a pair of ordinary sunglasses would likely have proved more cost effective. (Always assuming they do not turn into plasma when getting close to the sun...)

===Table of spectrum===
:This is the official image for {{w|Fraunhofer lines}} (solar spectrum) on Wikipedia:
:[[File:Fraunhofer_lines_From_Wikipedia.png|frameless|upright=.9]]
:The graph is a typical spectral lines chart, with a long rainbow band (from {{w|ultraviolet}} to the left to {{w|infrared}} on the right both colors appearing black as they are not visible.) The black lines in it, indicating the traces of different elements. Noe that the comic only covers the visible part of this spectrum.

*In the table below are the official labels from the picture above. If there are no label this is noted with ''none''.
**'''Note that they are labeled from right to left!'''
*Then the element causing the line is mentioned. ''Unlabeled'' is used if the line is not mentioned in the table from Wikipedia.
*Then follows the wavelength. It is given with decimals if it is noted in the table from Wikipedia. Else it has been read off manually from the picture above.
*Then follows the label given in this comic, with unlabeled meaning that it is not labeled in the comic but still shown. 
**If the line is not even included in the xkcd comic "N/A" will be used.
**A number will be given after the xkcd label listing which number line on xkcd that has used this label. (Note going from left to right in the numbering).
*Finally a comment can be made on this.
**If the two labels fit, then ''agreement'' is noted.
{| class="wikitable"
!Designation
!Element
!Wavelength ({{w|nanometer|nm}})
!xkcd label
!Comment
|- 
|A
|{{w|Oxygen|O}}
|759.370
|N/A
|This line is outside comics range. So are the two unlabeled lines shown in the spectrum in the picture above around 720 and 730 nm. There are also even more oxygen lines further out in the infrared part of the spectrum which is not even included in the picture above.
|-
|None
|Unlabeled
|690
|Those giant sunglasses 5
|This is the fifth of the five xkcd sunglass lines. This line is not labeled in the picture above. Wavelength read off manually 
|-
|B
|O
|686.719
|Oxygen 2
|Agreement 
|-
|None
|Unlabeled
|577
|Those giant sunglasses 4
|This is the fourth of the five xkcd sunglass lines. This line is not labeled in the picture above. Wavelength read off manually.
|-
|None
|Unlabeled
|660
|Unlabeled
|This line is not labeled either in the comic or in the picture above. Wavelength read off manually. It seems like this one was supposed to be one of the sunglasses lines, and then by mistake the arrow points to the labeled line C below.
|-
|C
|{{w|hydrogen|H}}
|656.281
|Those giant sunglasses 3
|This is the third of the five xkcd sunglass lines. This is actually the {{w|Hα}} line belonging to the {{w|hydrogen}} {{w|Balmer series}}. Seems like a mistake, and more likely it was meant for the arrow to point to the unlabeled line mentioned here above.
|-
|None
|Unlabeled
|645
|Those giant sunglasses 2
|This is the second of the five xkcd sunglass lines. This line is not labeled in the picture above. Wavelength read off manually.
|-
|a 
|O
|627.661
|Oxygen 1
|Agreement
|-
|D<sub>1</sub>
|{{w|Sodium|Na}}
|589.592
|Sodium 2
|Agreement. There are only one label (Sodium) in the comic above these two close lines.
|-
|D<sub>2</sub>
|Na
|588.995
|Sodium 1
|Agreement. There are only one label (Sodium) in the comic above these two close lines.
|-
|D<sub>3</sub> or d
|{{w|Helium|He}}
|587.5618
|N/A
|This line is so close to the nearest sodium line that only one line is visible, so only one is shown, both in the comic and in the picture above.
|-
|None
|Unlabeled
|577
|Those giant sunglasses 1
|This is the first of the five xkcd sunglass lines. This line is not labeled in the picture above. Wavelength read off manually.
|-
|None
|Unlabeled
|554
|Unlabeled
|Agreement. This line is not labeled either in the comic or in the picture above. Wavelength read off manually.
|-
|None
|Unlabeled
|549
|Unlabeled
|Agreement. This line is not labeled either in the comic or in the picture above. Wavelength read off manually.
|-
|None
|Unlabeled
|537
|Unlabeled
|Agreement. This line is not labeled either in the comic or in the picture above. Wavelength read off manually.
|-
|E<sub>2</sub>
|{{w|Iron|Fe}}
|527.039
|Iron 5
|Agreement.
|-
|b<sub>1</sub>
|{{w|Magnesium|Mg}}
|518.362
|Magnesium 2
|Agreement. See b below. There are only one label (Magnesium) in the comic above these two close lines.
|-
|b<sub>2</sub>
|Mg
|517.270
|N/A
|These two magnesium lines are so close that only one is visible in the spectrum, so only one is shown, both in the comic and in the picture above.
|-
|b<sub>3</sub>
|Fe
|516.891
|N/A
|This iron line and the next magnesium line are so close that only one is visible in the spectrum, so only one is shown, both in the comic and in the picture above. There is only one label for both visible lines showing them to be magnesium, even though there are four lines one of which (this one is Iron).
|-
|b<sub>4</sub>
|Mg
|516.733
|Magnesium 1
|Agreement. See b above. There are only one label (Magnesium) in the comic above these two close lines.
|- 
|c
|Fe
|495.761
|Iron 4
|Agreement.
|-
|F
|H
|486.134
|Hydrogen 3
|Agreement with {{w|Hβ}}.
|-
|h
|Unlabeled
|476
|Unlabeled
|Agreement. This line is also unlabeled in the table on Wikipedia. "h" is used between H and g below. The wavelength is manually read off from the image.
|-
|d
|Fe
|466.814
|Iron 3
|Agreement.
|-
|e
|Fe
|438.355
|Iron 2
|Agreement.
|-
|f
|H
|434.047
|Hydrogen 2
|Agreement with {{w|Hγ}}.
|-
|G
|Fe
|430.790
|Iron 1
|Agreement.
|-
|g
|{{w|Calcium|Ca}}
|430.774
|Calcium 3
|Agreement.
|-
|h
|H
|410.175
|Hydrogen 1
|Agreement with {{w|Hδ}}.
|-
|H
|Ca
|396.847
|Calcium 2
|Agreement.
|-
|K
|Ca
|393.366
|Calcium 1
|Agreement.
|-
|None
|Unlabeled
|389
|N/A
|This is the last line in the picture above. It is not included in the comic. There are even more lines outside the visible spectrum deeper into the ultraviolet which are not even shown in the picture above.
|}

==Transcript==
:[A chart shows the visible colored spectrum of the sun from deep violet to deep red. Along the spectrum are shown 28 black spectral lines of different thickness. Above the chart is a caption:]
:The Sun's spectral lines

:[Above the chart there are four and below the chart there are two labels, each label has one or more arrows pointing to different black lines. The two that has only one arrow points to two close lines marking them both. Only 22 lines are labeled like this, the other 6 are not labeled. The labels in reading order, with the number of arrows noted behind in square brackets:]
:Calcium [3] Iron [5] Sodium [1] Oxygen [2]
:Hydrogen [3] Magnesium [1] Those giant sunglasses [5]

==Trivia==
*Even though this comic was released on a Thursday, the scheduled Friday comic [[1734: Reductionism]] was still released as planned. 
**This was also the first time this occurred on xkcd - see [[1734:_Reductionism#Trivia|this trivia item]] from the next comic.

{{comic discussion}}

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