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View Full Version : When was the color of Neptune discovered?



Hans
2009-May-09, 03:49 PM
Was it by Voyager 2 in 1989 or earlier by ground based telescopes?

Or were they able to theorize what the color would be bluish based on the methane atoms detected?

TIA

schlaugh
2009-May-09, 04:05 PM
Thanks for the research (http://en.wikipedia.org/wiki/Discovery_of_Neptune)opportunity. :)

Apparently Galileo saw Neptune in December 1612 and again in January 1613 but noted it as a star and not a planet. A near miss.

The first observation was by Johann Gottfried Galle (http://en.wikipedia.org/wiki/Johann_Gottfried_Galle) in 1846 on the direction of Urbain Le Verrier (http://en.wikipedia.org/wiki/Urbain_Le_Verrier) who had mathematically predicted Neptune's existence and relative location.

My brief digging showed no reference to the color during the early observations but since Neptune resolves as a tiny blue dot with binoculars, you would have to believe that its true color was visible to Galle, et al.

Nowhere Man
2009-May-09, 04:38 PM
IIRC, the name was suggested by the blue color. That may be apocryphal, though.

Fred

Amber Robot
2009-May-09, 06:35 PM
I would imagine that with a halfway decent telescope and a slightly defocused image, the color would be readily apparent. However, I've not done the experiment, so can't say for sure.

StupendousMan
2009-May-09, 07:06 PM
I spent some time in the ADS

http://adsabs.harvard.edu/abstract_service.html

reading bits of old papers on this topic.
Most observers don't mention a color or
much of any description of the disk of the
planet. The few I could find are:

http://articles.adsabs.harvard.edu/full/1913AN....194..429S

T. J. J. See, using the 26-inch refractor of the
US Naval Observatory, wrote that the planet
appeared "of a greenish or greyish color."

http://articles.adsabs.harvard.edu/full/1928JRASC..22...20C

W. G. Colgrove, in a review article, states that
the planet glows "with a greenish blue tint similar
to Uranus."

Hornblower
2009-May-09, 08:11 PM
I have not been able to see vivid color, even with a 17.5 inch light bucket. It looks bluish gray to me.

George
2009-May-09, 09:05 PM
It is still a mystery why it appears so blue (especially blue when imgaed from space). It seems reasonable to assume some sort of chromophore (not just methane) absorbs the red end of the spectrum to the degree that blue dominates that which is reflected. The fact that Neptune's albedo is just about 80% of that of Uranus, thus more absorption seems likely for Neptune.

Oddly, Neptune is 18% more massive than Uranus, though 3% smaller in radius. But I would not assume a greater upper atmospheric density would be much of a factor to favor blue, even if such greater density exists there. Perhaps I am wrong, though.

tdvance
2009-May-09, 10:28 PM
Thanks for the research (http://en.wikipedia.org/wiki/Discovery_of_Neptune)opportunity. :)

Apparently Galileo saw Neptune in December 1612 and again in January 1613 but noted it as a star and not a planet. A near miss.

The first observation was by Johann Gottfried Galle (http://en.wikipedia.org/wiki/Johann_Gottfried_Galle) in 1846 on the direction of Urbain Le Verrier (http://en.wikipedia.org/wiki/Urbain_Le_Verrier) who had mathematically predicted Neptune's existence and relative location.

My brief digging showed no reference to the color during the early observations but since Neptune resolves as a tiny blue dot with binoculars, you would have to believe that its true color was visible to Galle, et al.

Are you thinking of Uranus? It is known he saw and plotted Uranus, and labeled it as a star.

a1call
2009-May-10, 12:15 AM
Some related quotes:


Small telescopes on Earth reveal a featureless greenish-bluish Neptune. (http://www.mira.org/fts0/planets/101/text/txt101x.htm)


Neptune's blue color is the result of methane in the atmosphere. Uranus' blue-green color is also the result of atmospheric methane, but Neptune is a more vivid, brighter blue, so there must be an unknown component that causes the more intense color that we see. The cause of Neptune's bluish tinge remains a mystery. (http://solarsystem.nasa.gov/planets/profile.cfm?Object=Neptune&Display=OverviewLong)

schlaugh
2009-May-10, 01:46 AM
Are you thinking of Uranus? It is known he saw and plotted Uranus, and labeled it as a star.

Well, I'm channeling Wikipedia so blame the source. :) But Neptune is mentioned in two separate references to the missed chance of Galileo. So it's possible the references are at fault.

George
2009-May-10, 03:02 AM
Surprisingly, there was an occulation of Neptune by Jupiter around 8pm January 3, 1613 as seen from Italy. Neptune appeared closer to Jupiter than the outer moons as early as Dec. 31st, 1612.

Wizard From Oz
2009-May-10, 03:04 AM
It has been a while, so maybe my memory is playing tricks, but I am sure I saw bluish-grey with my 8 inch Dob. It had a longer focal length than normal so not sure if that helped or not

George
2009-May-10, 03:06 AM
I would not be surprised if our atmosphere diminishes the blueness of Neptune, especially if it appeared anywhere near the horizon.

spin0
2009-May-10, 03:29 AM
I happen to have sir Patrick Moore's handbook "The observer's book of astronomy" from 1962. About appearance of Neptune it says: "Neptune reveals a small bluish disk" (pg.183).
Apparently Neptune's colour was known at least before 1962. And AFAIK it appears as a bluish disk in a moderately large telescope, so I believe it's bluish appearance has been known even well before 1962.

This might be little off-topic, but OP's question reminds me of a claim going around the web concerning one of our favourite crackpots Zecharia Sitchin. The claim is that in his book "The 12th Planet" (1976) he - or some ancient texts he so kindly "translated" to his readers - made a prediction about the bluish colour of planet Neptune. And not so surprisingly this blue colour was later confirmed by Voyager 2: in it's images Neptune really is blue as he is claimed to have predicted in 1976. It's amazing, isn't it. Except it isn't.

Hans
2009-May-10, 05:34 AM
Thanks for the information guys!

mike alexander
2009-May-10, 05:56 AM
You're welcome. For the record, in my 10" Uranus looks pale green, Neptune pale blue.

cjl
2009-May-10, 06:04 AM
I can definitely see some color when observing with a 10" in the mountains. It's not as vivid as the pictures from space appear, but there is a noticeable blue color. The lack of atmosphere at 10,000 feet might help though.

JonClarke
2009-May-10, 07:39 AM
The night of the Voyager flyby I saw Neptune through a 14" - definitely a pale blue.

Eroica
2009-May-10, 07:10 PM
Are you thinking of Uranus? It is known he saw and plotted Uranus, and labeled it as a star.It's true. Galileo observed and depicted Neptune in 1612 and 1613, but mistook it for a star. If he had kept observing Jupiter he would have seen the Jovian occultation of Neptune that George mentioned and would surely have realized that it must be a planet.

Eroica
2009-May-10, 07:22 PM
It is still a mystery why it appears so blue (especially blue when imgaed from space). It seems reasonable to assume some sort of chromophore (not just methane) absorbs the red end of the spectrum to the degree that blue dominates that which is reflected. The fact that Neptune's albedo is just about 80% of that of Uranus, thus more absorption seems likely for Neptune.

Oddly, Neptune is 18% more massive than Uranus, though 3% smaller in radius. But I would not assume a greater upper atmospheric density would be much of a factor to favor blue, even if such greater density exists there. Perhaps I am wrong, though.
The red photons are absorbed when methane molecules make large vibrational transitions (jumping from the lowest vibrational energy level to a much higher one in a single go). Perhaps there is just something about the conditions in Neptune's atmosphere that make these transitions more likely than is the case with Uranus. :think:

Although Neptune is much further from the Sun than Uranus, its effective cloud-top temperature is about the same (54 K).

George
2009-May-11, 03:51 AM
Perhaps there is just something about the conditions in Neptune's atmosphere that make these transitions more likely than is the case with Uranus. :think: Yes, perhaps, since Neptune does have more mass and less size, but I really know nothing of the differences in the upper atmospheres between the two planets.

Many seem to think there is another ingredient, a chromophore, that augments the red end absorption.