Talk:Pale Blue Dot

Wiki Education Foundation-supported course assignment
This article was the subject of a Wiki Education Foundation-supported course assignment, between 2 April 2019 and 28 June 2019. Further details are available on the course page. Student editor(s): Nickwogan.

Above undated message substituted from Template:Dashboard.wikiedu.org assignment by PrimeBOT (talk) 06:02, 17 January 2022 (UTC)

Carolyn Porco and Candy Hansen
NASA and JPL's Candy Hansen, and Carolyn Porco from the University of Arizona teamed up to calculate the exposure times for the images and they put together the command sequence to send to Voyager 1. These two should be mentioned in the article, per Sagan's Pale Blue Dot book, pages 4 and 5. Binksternet (talk) 17:45, 24 October 2011 (UTC)


 * I'm sorry, but couldn't find that particular info in the book . Suraj  T  05:44, 30 November 2011 (UTC)


 * Try scrolling down to Google Books page 5 which is listed on the page itself as page 4, meaning page 4 of the physical book. The relevant sentence in Sagan's book says, "The space scientists Candy Hansen of NASA's Jet Propulsion Laboratory (JPL) and Carolyn Porco of the University of Arizona designed the command sequence and calculated the camera exposure times." There ya go. Binksternet (talk) 05:52, 30 November 2011 (UTC)


 * Done. As for the rest of the article, I'm fairly sure that the article is now complete and IMO everything related to the the photograph available in the internet has been added and I've been thinking about nominating the article to be a featured article. And since you reviewed the article for GA status, I was hoping your opinion would be useful. Suraj  T  06:48, 30 November 2011 (UTC)


 * I will certainly take part in the FAC process. Binksternet (talk) 15:29, 30 November 2011 (UTC)

0.12 pixel?
The article states that the Earth is 0.12 pixel in size, which is contradictory because the pixel is the smallest possible picture element in an image, so I suspect this info is vandalism... can someone check it? Cogiati (talk) 04:19, 23 November 2013 (UTC)


 * I did some fixing up of the problem you encountered. First, the "reference" in the lead section was no good for anything so I threw it out. (It talked about "Dot Earth" which is not mentioned in the article.) Second, I tweaked the wording to say a fraction of a pixel. Third, I brought in an archived URL to make one of the 0.12-pixel references work better. Down in the article body, the 0.12 pixel size is well-supported by references. The pale blue dot is actually not a dot! Instead it is less than a dot—it is a mathematical calculation, with nearby pixels contributing some blue color. Binksternet (talk) 05:19, 23 November 2013 (UTC)
 * FWIW: Saying that the Earth occupies 0.12 pixels, could be interpreted as saying that each pixel in the image covers approximately 8.33 times as much sky as the Earth covers (8.33≅1÷0.12). Or, it could be the square of that—69.4 times as much sky. Either way, If one whole pixel happens to be brighter than the others, it's because that one pixel includes light received from Earth when the rest of them don't. 151.201.129.47 (talk) 20:40, 2 December 2023 (UTC)

How does Voyager continue to have power to travel and transmit radio signals?

71.237.124.157 (talk) 17:17, 6 February 2014 (UTC) Don Bray


 * All outer solar system probes, except possibly the latest Jupiter mission, rely on RTGs - radio-isotope thermoelectric generators. RTGs use the decay of radioactive material, usually plutonium, to generate electricity, since sunlight is too weak to furnish enough power.  Over time, as the radioactive material diminishes (half life), the power output decreases, and they have to shut down instruments to operate on the diminishing power supply.  Like you realizing you can't run your stove or dryer anymore, and then your TV has to stay off, and eventually you can only run a transistor radio or an LED night light.


 * I'd like to know what Voyager 1 saw - presumably primarily the northern hemisphere, but with Europe or North America in the foreground? It should be possible to calculate that, knowing its position by time of day and date, and which side of Earth was pointing that way nearly five hours before the picture was taken.  GBC (talk) 22:05, 16 April 2015 (UTC)

Earliest use of "pale blue dot"
I would like to add a reference to the first time Dr. Sagan publicly used this term and described the earth in the photograph as a pale blue dot. I am aware of his using this term in a commencement speech at the University of Illinois in May, 1990. In this speech, he also described the photo and explained that it would be published approximately one month from that day.

A recording of the speech is available at the Library of Congress here: http://www.loc.gov/item/cosmos000108/

I have not found an earlier use of the term, and since this use predated the release of the photo, I believe it was the first use. If anyone is aware of another earlier use, please share it. If there is no further information, I will edit the page to add this. — Preceding unsigned comment added by Blink440 (talk • contribs) 18:00, 10 April 2014 (UTC)


 * There seems a risk that what you are doing is original research, which cannot be our basis for a claim like "first use". What wording are you planning to use? HiLo48 (talk) 18:13, 10 April 2014 (UTC)

Cosmology portal
Why is this particular article linked to Portal:Cosmology? It doesn't seem relevant, at least not in comparison with "billions and billions" of other possible associations. Isambard Kingdom (talk) 18:14, 25 January 2015 (UTC)
 * Agreed. Although not completely unrelated, it's a bit of a stretch to consider a photo of a planet as a cosmology subject. --Deeday-UK (talk) 21:33, 25 January 2015 (UTC)
 * As it's THE 'only' planet that 'matters' in the scheme of things, seems it should be linked, don'tcha think? see below for a 'bad' link! 66.81.105.44 (talk) 10:26, 24 May 2015 (UTC)

"... as a perspective on our place in the universe."
If Sagan actually used this phrase, I seriously doubt it was in reference to the actual physical location of the Earth, so the wiki-link to that page is meaningless. 66.81.105.44 (talk) 10:39, 24 May 2015 (UTC)
 * Sagan's exact words (from ref No. 5 in the article) are:
 * ""But I thought that [...] such a picture might be useful nevertheless as a perspective on our place in the cosmos.""

- C.Sagan


 * Not sure what you read into it – feel free to elaborate on that point – but to me it means essentially what you mentioned, and the wiki-link makes perfect sense. --Deeday-UK (talk) 15:34, 24 May 2015 (UTC)

Photograph section, resolution
"Of the 640,000 individual pixels that compose each frame" The voyager camera seems capable of up to 800x800pixels. The Pale Blue Dot image measures at 453x614 pixels. Any idea as to the cause of discrepancy? I was not able to find any images corresponding to the full frame size from official sources. — Preceding unsigned comment added by TerryToogood (talk • contribs) 04:51, 2 November 2015 (UTC)
 * Source ref 14 in the article confirms that the resolution of the narrow-angle camera's sensor was 800x800 pixels. I can only guess that NASA published either a cropped or a lower-resolution version of the original image. --Deeday-UK (talk) 16:01, 2 November 2015 (UTC)

Quote by Sagan
Reading WP:COPYQUOTE, it doesn't seem to me that the previous quote in full from Sagan was falling foul of the policy. It wasn't a substantial part of the book (it wasn't even part of the book proper, just the introduction, as I understand it), and – considering that without Sagan and his ideas there would have been no photograph and no Wikipedia article – it seems pretty relevant to the subject matter, in my view.

In any case, there is a source containing something shorter and even more relevant: an excerpt from the speech that Sagan gave at Cornell Uni, largely, but not completely, the same as the passage in the book, but also with a passing reference to the mission. Now partially quoted in the article. --Deeday-UK (talk) 23:18, 21 June 2016 (UTC)

Quote by Sagan – 2
The current quotation by Sagan is taken from a speech he gave at Cornell University in 1994, as reported by the source ref. 21. The quoted portion of the speech clearly shares much of its content with Sagan's introduction to his book Pale Blue Dot: A Vision of the Human Future in Space, but that doesn't mean that it is the speech that cites the book; it may well be the other way round. Both the speech and the book are dated 1994.

In any case, between the speech and the book, the speech is arguably more relevant, because it focuses on the Pale Blue Dot photo itself, even mentioning the mission work ("We succeeded in taking that picture…") while the book is centered on a different subject (i.e. human colonization of outer space), and Pale Blue Dot is mentioned only to introduce the subject (see the words "Visit, yes. Settle, not yet", which are missing from the speech and clearly refer to the book's topic, not to the photo of Earth in question).

With regard to copyright, neither I think that there is a particular problem. However, not long ago another editor questioned the excerpt as a possible copyright violation, so, to err on the side of caution, better to quote the speech instead, which is more relevant and is also a public addressing, as opposed to a published work of literature. Deeday-UK (talk) 16:38, 2 August 2016 (UTC)


 * You convinced me. Good argument. Binksternet (talk) 17:08, 2 August 2016 (UTC)

What side?
What side of the Earth are we looking at, at that time and date, from that location? Just want to know if my house is in that picture. Correctrix (talk) 07:52, 30 October 2018 (UTC)


 * It was photographed at 04:48 GMT. If we round to 05:00 GMT noon at this time would be GMT+7 and midnight GMT-5. There is an image in the article which shows the position of the Earth and Sun at the time. From the perspective of Voyager 1 the Sun and Earth are aligned and it is observing from the western side. Therefore we are roughly looking at the time zones between GMT-5 and GMT+7. Lightbloom (talk) 15:05, 8 September 2023 (UTC)
 * The speed of light also needs to be considered since Voyager 1 is so far from Earth. According to the article it took five and a half hours for a radio signal from Voyager 1 to reach Earth at the time. If we are looking at light from five and a half hours ago, the time zones on Earth we are observing would be between GMT-10.5 and GMT+1.5 instead. Lightbloom (talk) 15:17, 8 September 2023 (UTC)

Why is Earth a Pale Blue Dot?
I added a section titled "Why is the Earth a Pale Blue Dot?" It seemed reasonable to put this section after the background, but I think it would fit well in other parts of the article too. Nickwogan (talk) 20:45, 10 June 2019 (UTC)
 * Thanks. I changed the section heading a bit and moved it lower on the page. It's a good addition in my opinion, and educates the readers. Would something similar work within The Blue Marble page? Randy Kryn (talk) 21:17, 10 June 2019 (UTC)
 * Ok sounds great. This might also apply to the blue marble image, but I am not certain. I'll read up on it.Nickwogan (talk) 23:38, 10 June 2019 (UTC)

I have moved and reduced the section to something more similar to how it was before. Bear in mind that this article is about a famous photograph, not about the physics of the atmosphere; all those fine details about wavelengths and spectra are way over the top here, and belong instead e.g. to the Diffuse sky radiation article (which is now linked from this one). Also, I've removed the part about clouds making the blue pale rather than dark because it appears to be original research. I haven't found mention of it in the given sources. --Deeday-UK (talk) 12:09, 11 June 2019 (UTC)
 * Thanks for the edits. I like most of them except removing the part about clouds causing the Earth to be pale blue. This journal article states that ″The Earth is pale blue rather than deep blue because white clouds enhance reflectivity at all visible wavelengths and thus reduce the relative intensity of the Rayleigh tail.″Nickwogan (talk) 18:59, 11 June 2019 (UTC)
 * I see; happy with that. I've clarified it further. --Deeday-UK (talk) 00:49, 12 June 2019 (UTC)

Deeday-UK I expanded this topic into its own section one more time. I tried to used fairly straightforward language while still being accurately. Let me know what you think. Feel free to change it back to a sub-section if you think that is better. Nickwogan (talk) 23:53, 12 June 2019 (UTC)
 * The section seems fine, and gives a good encyclopedic explanation of a relevant topic to the article. Since the page is named Pale Blue Dot then the "why" comes into play, with the new well-written explanation. p.s. and as I look at it the lower-cased wording in the section head seems better than upper-cased. Randy Kryn (talk) 00:04, 13 June 2019 (UTC)


 * Please note that the phrase "Pale Blue Dot" is now used in the astronomical literature to refer to the Earth (or an Earth twin exoplanet) captured as a single pixel in a telescopic observation, such as in the cited reference above but also others. The phrase is used particularly with reference to future direct imaging of exoplanets and the search for life elsewhere. So, the lead of the article is not really up-to-date because "Pale Blue Dot" has acquired additional meaning beyond just a photograph. Because of this other contemporary usage in astronomy, it is appropriate for the Wikipedia page to explain why the Earth has the color of pale blue in a single pixel and the interesting fact that's it's related to a biosphere affecting the Earth's air. DCCProf (talk) 01:42, 13 June 2019 (UTC)

I have no objections to a separate section for the color discussion, but I've changed the section's heading to something more encyclopedic. Headings are not usually full sentences, and the old one was also inconsistent with the rest of the article. The wording was also inaccurate: the Earth is not a pale blue dot; the Earth is a planet. The section could do with some more tweaking too. --Deeday-UK (talk) 10:02, 13 June 2019 (UTC)

Thanks for the edits. I agree that the “Earth is not a pale blue dot” but a planet. Instead, I was making the point that the scientific literature in astronomy and astrobiology uses the phrase “pale blue dot” to refer to a single pixel (or broadband spectrum without spatial information) captured by remote sensing of the Earth or an Earth twin exoplanet. The phrase has moved beyond just referring to the Voyager 1 photograph or the title of Sagan's book. A selection of examples (by no means exhaustive) with links that demonstrate this fact over the last 15-20 years are as follows,


 * R. Irion, The Search for Pale Blue Dots. Science 303, 30 (2004). https://science.sciencemag.org/content/303/5654/30


 * Grenfell J.L., Rauer H., von Paris P. (2013) Exoplanets: Criteria for their Habitability and Possible Biospheres. In: de Vera JP., Seckbach J. (eds) Habitability of Other Planets and Satellites. Cellular Origin, Life in Extreme Habitats and Astrobiology, vol 28. Springer, Dordrecht https://doi.org/10.1007/978-94-007-6546-7_2 In the book chapter: “Clearly, for exoplanet studies, only remote detections are feasible. A main challenge will be to extract potential information from (likely) very low spatially resolved exoplanetary spectral data – sometimes referred to as the “pale blue dot” problem.”


 * T. D. Robinson et al., Detection of ocean glint and ozone absorption using LCROSS Earth observations. Astrophys. J. 787, 171 (2014). https://iopscience.iop.org/article/10.1088/0004-637X/787/2/171/meta In the article: “Studies aimed at interpreting observations of the unresolved Earth (the "Pale Blue Dot") are hindered, in part, by a paucity of data suitable for such work.” “…models are instead used to simulate photometric and spectroscopic observations of the Pale Blue Dot.” “Typically, the VPL Earth model is used to generate phase-dependent disk-integrated spectra of the Pale Blue Dot.”


 * E. Pallé, M. R. Z. Osorio, R. Barrena, P. Montañés-Rodríguez, E. L. Martín, Earth’s transmission spectrum from lunar eclipse observations. Nature 459, 814 (2009). https://www.nature.com/articles/nature08050 In the article: “Because of the blue colour, when observed from an astronomical distance, the Earth is often referred to as the pale blue dot, but in transmission, the pale blue dot becomes the pale red dot.”


 * G. Arney et al., The Pale Orange Dot: The spectrum and habitability of hazy Archean Earth. Astrobiology 16, 873-899 (2016). https://doi.org/10.1089/ast.2015.1422 In the article: “Colors and photometric bands have been considered as indicators of Earth-like worlds (Traub, 2003; Crow et al., 2011; Krissansen-Totton et al., 2016), but hazy Archean Earth suggests that not all Earth-like planets will be pale blue dots.”


 * Wolstencroft, R. D. & Breon, F.-M. Polarization of Planet Earth and Model Earth-like Planets, Astronomical Polarimetry: Current Status and Future Directions ASP Conference Series, Vol. 343, Proceedings of the Conference held 15-19 March, 2004 in Waikoloa, Hawai'i, USA. Edited by A. Adamson, C. Aspin, C. J. Davis, and T. Fujiyoshi, p.211 http://adsabs.harvard.edu/full/2005ASPC..343..211W In the article: “In calculating the polarization of a Pale-Blue-Dot Earth (at a given wavelength and scattering angle), we summed the values of the polarized reflectance for each class…”


 * J. Morse et al. (2018) Project Blue: Visible Light Imaging Search for Terrestrial-class Exoplanets in the Habitable Zones of Alpha Centauri A and B, White paper submitted to the Exoplanet Science Strategy study of the US National Academies of Sciences https://arxiv.org/abs/1803.04872 In the article: “Project Blue’s goal is to perform a direct imaging survey of the habitable zones of Alpha Cen A & B in visible light, to determine whether a “pale blue dot” exists around our nearest stellar neighbors. “

DCCProf (talk) 19:44, 13 June 2019 (UTC)
 * N. J. Woolf, P. S. Smith, W. A. Traub, K. W. Jucks, The spectrum of earthshine: A pale blue dot observed from the ground. Astrophys. J. 574, 430-433 (2002). https://iopscience.iop.org/article/1


 * This article is about a specific photograph. If there are other meanings of the term "pale blue dot" that refer to notable topics they should be covered by other articles (and linked from the dab page, see-also etc if appropriate). DexDor(talk) 20:05, 13 June 2019 (UTC)


 * Agreed. Yes, a separate article would be the appropriate approach for the astronomical remote sensing meaning. DCCProf (talk) 20:46, 13 June 2019 (UTC)

2020 commemorative (and the 2013 version)
Hello. I had added to the caption of the 2020 commemorative photo manipulation (and been reverted by ) that the Earth has been enlarged in this version, as mentioned in the text, but this isn't clear from the sources and image page which still say it's one pixel in size. Brightened considerably, yes, but the enlargement isn't clear. Having put the image up, what's your take on this. Maybe more importantly, upon seeing the Earth portion of the 2013 image The Day the Earth Smiled it should probably be used on this page (it's a beautiful image). Thoughts and musings? Thanks. Randy Kryn (talk) 12:08, 18 April 2021 (UTC)
 * and others: Hello Randy - Thank you for your comments - and efforts with this - for my part, at the moment, I'm inclined to agree with Deeday-UK - the current caption (ie,  Pale Blue Dot Revisited, 2020) seems entirely ok - and sufficient - further image details are in the text and image description - fwiw - seems similar - and better - than my original caption (ie, Pale Blue Dot – updated version (12 February 2020)) - in any case - hope this helps in some way - Thanks again for your comments - and - Stay Safe and Healthy !! - Drbogdan (talk) 12:35, 18 April 2021 (UTC)
 * Yes, but is the Earth enlarged or just made brighter by contrast? The text is unclear of what has been enlarged, the entire image or the dot of Earth ("Brightness levels and colors were rebalanced to enhance the area containing the Earth, and the image was enlarged, appearing brighter and less grainy than the original.")? A bit confusing as to what is being described, and if it is the Earth that is enlarged then a caption explanation is arguably appropriate. Thanks . Randy Kryn (talk) 12:45, 18 April 2021 (UTC)
 * Thanks for your recent comments - yes - I understand - perhaps your excellent views of the image details could be part of the related text in the article in some way, but not in the image caption imo atm - on a related issue - not entirely sure whether the 2013 image should be added in the article - it's a worthy image to be sure, but perhaps not exactly in keeping with the original purpose of the article - which focuses on the particular February 14, 1990 ("Pale Blue Dot") image by Voyager 1 - Stay Safe and Healthy !! - Drbogdan (talk) 13:00, 18 April 2021 (UTC)

Randy Kryn, what NASA did was to enlarge the whole image from the original 800 x 800 px to over 5,000 × 5,000 px, then presumably they smoothed out the light bands and sharpened the image of the Earth, apart from adjusting contrast, brightness, colors etc. --Deeday-UK (talk) 19:24, 18 April 2021 (UTC)
 * Interesting, thanks. Randy Kryn (talk) 03:48, 19 April 2021 (UTC)

There's another photo with "pale blue dot" in its name
They call it, "Cassini's Pale Blue Dot." Taken by the Cassini–Huygens spacecraft while orbiting Saturn. https://www.esa.int/ESA_Multimedia/Images/2013/07/Cassini_s_Pale_Blue_Dot Might be worth a "See Also..." 151.201.129.47 (talk) 20:44, 2 December 2023 (UTC)