1517: Spectroscopy

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Although right now I'm more excited about ESPRESSO's radial velocity measurements, so I'm listening to This Kiss, her song about measuring "centrifugal motion" on "a rooftop under the sky".
Title text: Although right now I'm more excited about ESPRESSO's radial velocity measurements, so I'm listening to This Kiss, her song about measuring "centrifugal motion" on "a rooftop under the sky".


This comic mixes the method of using spectroscopy to detect oxygen on exoplanets (planets outside our Solar system) with the lyrics for the Faith Hill song "Breathe" (listen to "Breathe" on YouTube).

From the lyrics:

I watch the sunlight
dance across your face


I can feel you breathe

In the comic the word "feel" has been changed to "see". The two first panels are one line in the song. The last line is from the chorus and is repeated five times during the song, although not right after the first two lines.

In the first and second panel the singer examines the spectra of a remote planet by watching the sunlight during the transit of the planet as this sunlight dances across the planet's face. Finally we determine that breathable oxygen exists. Since we cannot (as Faith can) feel the planet we have to see it. And by doing this I can see you breathe.

Measuring the light output of stars (spectra) we are able to determine a number of details of the star, including rotation, relative radial velocity, chemical composition, temperature, and to some degree, distance and size. When a planet, as pictured, moves between the star and the observer, then by looking at the spectrum received, the viewer is able to determine the contents of the planet's atmosphere from the specific wavelengths of light that are absorbed in this. If it turns out that the atmosphere absorbs the lines corresponding to molecular oxygen (O2) this is a clear indication that the planet has large quantities of breathable oxygen (but not necessarily life). However, there must be oxygen in large amounts in the atmosphere to sustain most of the life forms that we know of here on Earth (though not all). It is thus clear why Randall would be interested in exoplanets with oxygen.

This comic came out four days after this article about NASA's New NExSS Initiative. NASA will search for signs of life on other planets, for instance by using "the light passing through the atmospheres of these exoplanets". And they "will study chemicals that have been detected on other worlds, such as oxygen and methane, to see if they were produced by biology".

The title text refers to determining radial velocity in the ESPRESSO program (Echelle SPectrograph for Rocky Exoplanet- and Stable Spectroscopic Observations). By noting that the radial velocity of the star changes slightly as the planet that orbits it moves around the star (centrifugal acceleration), the ESPRESSO program should be able to detect the masses of planets as they are moving towards the Earth in their orbit around their distant stars. The ESPRESSO program is so precise that it should be able to detect planets as small as Earth and the other of the Solar system's inner planets.

Randall is now even more excited about ESPRESSO than he is about the oxygen levels, because it is now possible to detect these "very" small planets. So he is no longer listening to "Breathe", but to another Faith Hill song: "This Kiss" (listen to "This Kiss" on YouTube).

From the lyrics:

It's centripetal motion


On the rooftop under the sky

The first line is part of the chorus and it is repeated four times, but Randall has changed the main word to "centrifugal". There is, however, disagreement on-line whether it is centripetal or centrifugal.

The second line is not sung in connection with the chorus, and it is only changed a bit, so "the" is changed to "a". Also the "on" which is part of his line here is not part of the quoted line in the title text.

The song is not about measuring but, of course, about "The Kiss". Since the ESPRESSO is part of the Very Large Telescope, it is located on the Cerro Paranal mountain in the Atacama desert in Chile at an elevation of 2,635 meters (8,645 ft.) above sea level. So it could be said that it is measuring on a rooftop under the sky. Although it is radial velocity it measures, not centrifugal motion, the object it does measure will all be experiencing this fictitious force (also see 123: Centrifugal Force), as the planets are in orbit around a star.

Randall has previously made several references to exoplanets in his comics, most notable are the two comics with the same name: 786: Exoplanets and 1071: Exoplanets. The latter comic came out when there were exactly 786 exoplanets found. Today more than 1900 have been discovered (1915 as of Wikipedia on the release day of this comic), much more than twice that amount. And now they can find even smaller planets, and detect the atmosphere. Much have happened since the first exoplanet comic came out in 2010. Five comics later in 1522: Astronomy he mentions astrobiology in the title text, closely relating it to this comic.


[A dark panel with a bright star in the center. To the left a planet (drawn as a new moon) approaches the star. Text is written above in white with two musical notes, one on each side of the text.]
I watch the sunlight
[Same image but now the planet transits the star. Small lines around the planet indicate the atmosphere, as seen from the light from the star passing through it. Text is again written above in white with two different musical notes, one on each side of the text.]
Dance across your face
[A white frame with a black line. It Is the spectrum of the planets atmosphere. Two distinct absorption peaks are visible. The first one is labeled with an arrow. Text is again written above, now in black, with two, again, different musical notes, one on each side of the text.]
I can see you breathe
Label: O2
[Below the panels is the following caption:]
Faith Hill on exoplanet spectroscopy

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Thanks, Kynde, for the nice explanation. 13:29, 27 April 2015 (UTC)

Your welcome, and Thanks. I think I was still working on it when you wrote this comment ;-).--Kynde (talk) 13:42, 27 April 2015 (UTC)

I was wondering how many people go to watch these two songs on YouTube today (and the next few days) solely because of Randall's comic. I have long time wondered about this. Now maybe a time to find out. Of course we never know in advance how many new hits the song he chooses received the days before. But now we have a chance of following it over the next few days. Of course the comic has been up several hours but it is still early across most of the US... Here are the counters for the two videos linked above in the comic as of right before this post was made: Breathe: 9.493.222 and This Kiss 4.079.410. Please feel free to add new counts a few times over the next week or so. :-) --Kynde (talk) 13:42, 27 April 2015 (UTC)

Links for your convenience: "Breathe", "This Kiss" and as control "Cry".

"Breathe" 9,493,334, "This Kiss" 4,079,458, "Cry" 3,182,592 13:54, 27 April 2015 (UTC)

Thanks. Here goes after 1 day and 2 hours:
9.500.026 (+6692/+,07%)
4.083.297 (+3839/+,09%)
3.184.334 (+1742/+,05%)
I'm nut sure we can learn anything from this yet...?--Kynde (talk) 13:55, 28 April 2015 (UTC)

Actually, if the star or region of space is anything similar to our own, O2 is definitively a sign of life. Not animal life, but at least plant life, to crack the O2 out of the CO2 with photosynthesis.Seebert (talk) 14:00, 27 April 2015 (UTC)

The explanation currently covers links that show that not all oxygen will be created because of life, and not all life (even 'as we know it') will necessarily require/produce a significant oxygen signal. But there seems to be a missing middle-bit in that oxygen initially seems to have been a smothering 'industrial pollutant' by early (oxygen splitting) life-forms until other life-forms developed the machinary to use this oxygen as part of their own energy mechanisms (creating the eventual two-way dynamic of CO2 and O2 production/usage between the major groups of life) and thus making the unstable free oxygen both an indicator of life and an indicator of the capability of life (by mainstream terrestrial standards of biology, of course). 18:06, 27 April 2015 (UTC)
That is not necessarily true. There is now a theory that oxygen could be have been created without life involved here on Earth based on the snow ball earth scenario. In the ice H2O2 formed and when the ice melted this was released into the water where it then would release oxygen. See for instance here: Did snowball Earth's melting let oxygen fuel life?. --Kynde (talk) 14:09, 28 April 2015 (UTC)

I'm pretty sure the original lyric for "This Kiss" is "it's centripetal motion" (see: http://www.sweetslyrics.com/59372.Faith%20Hill%20-%20This%20Kiss.html). I assumed the joke Randall was making was that centrifugal really is a force, Mr. Bond, even if Faith Hill doesn't know about it. Djbrasier (talk) 00:25, 28 April 2015 (UTC)

I agree: I only recall hearing "centripetal motion", but Google tells me there are actually more hits for "centrifugal", and that there are some lyrics sites putting both phrases in the song. Mark Hurd (talk) 01:41, 28 April 2015 (UTC)
I think the song says "centrifical" which is not even a word, let alone a force, ficticious or not. Nonetheless, it seems to be a common misspelling since it has its own wiktionary entry (http://en.wiktionary.org/wiki/centrifical). 08:54, 28 April 2015 (UTC)
I agree that she doesn't sing centrifugal. I have changed the explain to say it is centripetal (I'm sure she is supposed to at least, maybe she doesn't know the word either ;-) But left in a comment on the fact that there are different versions on-line. But I'm sure that that is because people do not know the word centripetal and also that people who make lyrics pages cut and paste from each other. I have often seen the same mistake on several lyrics pages. --Kynde (talk) 13:50, 28 April 2015 (UTC)
Its not centripetal, she sings "centrifugal" but with pronounced wrong. Its a pop song, and centrifugal with a long u wouldn't fit, so the i is short but stressed, and the u is reduced to a schwa. Rightly or wrongly, "centrifugal" is the common word. 18:37, 28 April 2015 (UTC)
How is it pronounced wrongly? There's two pronunciations for the word "centrifugal," and one of them is without a long-U sound. /sɛnˈtrɪf yə gəl, -ə gəl/ (see: http://dictionary.reference.com/browse/centrifugal?s=t) Maybe she's a bit harder on the G than might be proper, but most people I know pronounce it as she does, or close enough anyway. -- 03:20, 29 April 2015 (UTC)
I believe a close viewing of the linked official video of "This Kiss" makes it certain that Ms. Hill is singing "centrifugal". To see this, examine some frames near 0:33, when Ms. Hill is singing "centrifugal" for the first time. Although (so far as I can tell) YouTube does not support frame-by-frame advance, you can hit play and stop in rapid succession, and convince yourself quite thoroughly that Ms. Hill's top teeth are always visible, and that her lips never meet. Compare this to the very first frames of the cut at 1:19 when Ms. Hill is just beginning to sing "pivotal". You will very clearly see her lips touching and slightly pursed. (Is there a way to attach screenshots?) Given that it is impossible to pronounce a "p" phoneme without the lips coming together at some point, Ms. Hill is not singing a word with a "p" in it at 0:33, but rather one with an "f," pronounced with the top teeth touching the bottom lip -- "centrifugal," in fact. Conclusion: Randall is quoting the actual lyrics intended by the singer on the official video. 01:21, 30 April 2015 (UTC)