Happy birthday, Neptune!

By Phil Plait | July 12, 2011 6:00 am

Today is special: it is now one full Neptunian year since this giant planet was discovered in 1846!

So today is Neptune’s birthday! Um. Well, kinda.

Yeah, as usual, stuff like this gets complicated. I realized this anniversary was coming up about a year ago, and contacted an old friend about it: Kelly Beatty, editor at Sky and Telescope magazine, who then contacted astronomers John Westfall and Roger Sinnott. We had some fun email exchanges about all this! I think I have a good grip on this now, so let me explain.


The short form

First, to celebrate a birthday, you need the birthdate. That’s the first complication. Neptune was discovered on September 23, 1846 by astronomer Johann Galle using star charts by Johann Encke, and they are generally given credit for it. However, that date of September 23 is a bit dicey! Galle and Encke report that they found Neptune on 9/23 at 12:00:15 "Berlin M.T.", according to Westfall. But they reckoned the day starting at noon! And since they’re using Berlin mean time, you have to account for the longitude of Berlin with respect to 0° longitude on Earth. According to Westfall, once you do all that, you get a discovery time of September 23 at 23:06:40.

Worse yet, there may be some imprecision in the exact time the astronomers reported the discovery, although Galle reported the time to a fraction of a second. Westfall reports that might be as much as 1.2 hours, preferring a discovery time of September 24, 1846 at 00:15 GMT.

Who’s right? Turns out, it doesn’t matter much, since we only need to know the time to within a few hours to get the right date for the birthday. Still, Westfall appears to have looked at this pretty hard, so you know what? Good enough. I’ll use his numbers.


A year by any other name would take as long

OK, so we have the birthdate. Now, how long is a Neptune year?

Yeah, well, that turns out not to be so easy to answer either! There are lots of ways to measure a year. And worse, Neptune’s year isn’t constant; the gravity of Uranus tugs on Neptune, accelerating it, changing its period around the Sun. The effect is small, but measurable, and in fact it was Neptune’s effect on Uranus that allowed astronomers to find it in the first place! So the time it takes Neptune to circle the Sun once changes over time. Arg.

But there’s a way to cut through that: instead of trying to figure out Neptune’s exact period and adding it to the discovery date, we can ask when Neptune returns to the same position in the sky where it was when it was discovered, call that one Neptunian year, and be done with it. Doing that based on the Neptune’s position as seen from Earth is complicated (of course) and is biased. After all Neptune is orbiting the Sun, not Earth.

In fact, it’s not that simple (stop me if you’ve heard that before). Neptune actually orbits the solar system’s barycenter, its center of mass. You might think that would be the center of the Sun, but Jupiter is big enough to pull on the Sun a bit, making the entire solar system off-center (think of it like an adult and child holding hands and spinning around; the mass of the kid pulls the grownup a bit off-center as they circle each other — or just look at the animation here and let yourself get dizzy). The other planets contribute as well. This makes things a lot harder to figure out, and this is getting ridiculous as it is. [Note added after I finished this article but before it got posted: Tammy Plotner at Universe Today does in fact go into the barycenter argument, and correctly concludes that yesterday was the barycentric Neptunian birthday. It comes down to a matter of preference, I think.]

So instead, let’s simplify (yay!), pick a coordinate system based on the center of the Sun, get the coordinates of Neptune when it was discovered, and then figure out when it returns to those same coordinates. We can use Neptune’s heliocentric longitude to do this.

Heliocentric longitude and latitude are like their counterparts on Earth, except measured from the center of the Sun. And instead of using Earth’s equator as we do for long and lat on Earth, for the heliocentric coordinates we use the Earth’s orbit around the Sun! That defines a plane on the sky just like the Earth’s equator does on the Earth’s surface. And just like 0° longitude on Earth is arbitrary (it passes through Greenwich, England, where the coordinate system was defined), heliocentric longitude has its zero point as the position on the sky of Earth’s vernal equinox, where the Earth’s orbit intersects the projection of the Earth’s equator on the sky.

Yeah, I know. This makes my head hurt sometimes too. I think what’s most frightening about all this is that I understand it. Still, the diagram here (click to embiggen) shows the layout. All you really need to know is that the yellow line there points to 0° heliocentric longitude in the sky. Think of it as a benchmark. Halfway around the sky is 180° longitude, and so on.

So imagine you were at the center of the Sun (wearing sunblock 1012) in 1846 and looking at Neptune at the moment humans on Earth discovered it. You ask yourself, "How far east is Neptune at this moment, as measured from 0°?" The number you get, if you’re using Westfall’s time and date of discovery, is 329° 05’ 51.5”. OK, cool.

Then you wait about 165 years. At some point, Neptune will have that exact same longitude again. When is that date? Drum roll please…

July 12, 2011, at 18:38 GMT

Aha! So why not use that? If you live in the US, at 14:38 Eastern time, Neptune will have completed one circuit around the Sun since it was discovered, according to its own calendar.

Phew! And as you can see, if we’re off by a couple of hours either way, the date stays the same for us here in the States. I’m good with that.

Oh — by the way, we can use these numbers to then ask how long Neptune’s year is. The amount of time between these two dates is 60,191.8 days, or 164.8 Earth years. On Neptune, I’d only be a little over 3 months old.


This too shall pass

I almost hesitate to mention that as seen from Earth, Neptune will pass this same spot in the sky not once but five times! That’s because the Earth is moving around the Sun as well, and our perspective changes. Explaining it here will make both our heads explode, so I’ll just link to a video of Brian Cox talking about it. He does a great job. But if you’re keeping track at home, according to Westfall Neptune has already passed this position in the sky as seen from Earth three times (in April and July 2010, and in February in 2011) and will again twice more this year (in October and November).

But at this point I’m done. July 12 is good enough for me.


Bismillach, NO!

So we can finally, safely, say "Happy Birthday, Neptune!" today.

Right? Right?

Well… I’d hate to point it out, but it’s been shown that Galileo actually saw Neptune on December 28, 1612, and thought it was a star. He observed it again a month later. Had he noticed that particular "star" had moved, we’d be doing even more math here. Too bad, though. If Galileo had been able to figure out what he saw, why, he’d have been famous!

But I think we can ignore that, since Galileo didn’t know he had seen it. Galle gets the credit, so his date is the one we’ll use.

Yay!

So here we are, one full Neptunian revolution after it was first found. It’s kind of a fun thing to think about today; how even something as trying to figure out the orbit of a major planet can be such a pain in the butt. You can try to observe Neptune itself, too, if it’s clear where you are and you have binoculars.

And if you’re wondering how I’m going to celebrate, why, I’m going to sit back and eat a Krabby Patty?.

http://www.youtube.com/watch?v=61_jG2aa7GY

Credits: Neptune: NASA; barycenter animation and ecliptic diagram: Wikipedia.


Related posts:

- Happy new year (again)!
- Why, King Triton, how nice to see you!
- Planet pr0n
- Is there another planet in the solar system?

CATEGORIZED UNDER: Astronomy, Cool stuff, Top Post

Comments (45)

  1. Chief

    Wow, makes me appreciate the calculations for placing a probe to the correct orbit around a planet and knowing it years beforehand.

  2. alfaniner

    I learned a new word today. “Barycenter”.

  3. Fraloob

    Wow! I really enjoyed reading that. Can’t say I really understood it, but it was fun! Thank you.

  4. Mapnut

    Not birthday. New Year’s Day.

    Boy, Neptune takes the long way around. Someday I must get a good telescope and look for it. Love Gustav Holst’s interpretation.

  5. Messier Tidy Upper

    Happy “birthday” – or perhaps make that anniversary (or maybe that’s not the right word either? hmm?) – Neptune! :-D

    EDIT : Ah yes – Happy New Neptunean Year -thankyou (#3.) Mapnut. :-)

    Here’s a Sea-God’s trident of links to celebrate the occassion :

    http://www.youtube.com/watch?v=76xz74X4ivw

    &

    http://www.youtube.com/watch?v=wriUZ8J0Ofw&feature=related

    Courtesy of “AggManUK” on the other blue planet and its ice moon of the methane geysers.

    Plus here’s the Neptunean planetary anthem :

    http://www.youtube.com/watch?v=6N6Chjyuf7o

    Courtesy of Gustav Holst. ;-)

    Plus a great quote or three for y’all :

    Neptune’s mean distance from the Sun is 2,783 million miles; it takes 164 ¾ years to complete one revolution. … Neptune’s ‘day’ is now believed to be about 17 hours and 40 minutes, so there are over 80,000 Neptunian ‘days’ in every Neptunian ‘year’.
    - Page 57, ‘The Sky at Night’, Patrick Moore, WW. Norton & Co, 1986.

    Neptune is both smaller and denser than its “twin” Ouranos – so while it would take 14 Earth’s to match Ouranos, but it would take 17 Earth’s to match Neptune.
    - P. 57, ‘The Sky at Night’, Patrick Moore, WW. Norton & Co, 1986.

    “If it were possible to drive straight from the Earth to Neptune, taking the shortest possible route and keeping up a steady 60 m.p.h., the journey would take nearly 5,200 years.”
    - Page 57, ‘The Sky at Night’, Patrick Moore, WW. Norton & Co, 1986.

    By the way, the Voyager II fly-past of 1989 was one of the events that really triggered my personal love of astronomy. We knew so little of it before and saw it only so dimly.

  6. Georg

    The discoverers name was “Johann Gottfried Galle” , and when You look at
    his portrait at :

    http://de.wikipedia.org/wiki/Johann_Gottfried_Galle

    You will “see” that he would not like to be called “John”! :=)

    Regards
    Georg

  7. Mejilan

    What a silly, lazy little planet! She’s a beaut, though, so we can forgive her. Right?

  8. Is Neptune the planet with the lowest albedo ie. the darkest of all the planets in visible light?

    Had the lights off in the lounge room as the sunset today. I was looking at a poster of the planets of our solar system (as seen in visual light, true colour I think) on the wall. Watched as it grew darker and noticed Neptune faded into black very quickly whereas Ouranos stod out for longer than the others. Could just be the specific pictures chosen but, has got me wondering now.

    Could that in part explain why it is hotter than or at least as warm as Ouranos despite being further away? The dark clouds of neptune absorbing more heat contrasting with the lighter clouds of Ouranos reflecting more of what feeble sunlight there is out there away over the ast spandss of time. Has someone, anyone, calculated this yet and worked out how much difference the darker shade of blue makes for Neptune as opposed to Ouranos’es paler more reflective sheen?

    Does anyone know and care to enlighten us, please?

  9. Regarding the barycentre, Tammy Plotner’s calculation results giving the 11th July originally came from this post, and the reason for preferring to think of the orbit as being around the barycentre rather than the Sun can be summed up in two nice little plots: Neptune-Sun distance and Neptune-barycentre distance. Spot the difference.

    Of course there are reasons to prefer fixing on the Sun too, so it is a matter of taste, but to me they don’t compete with the fact that, relative to the barycentre, the motion is a lovely smooth approximation to a Keplerian elliptical orbit while the Sun does its own wiggly dance in the middle.

    It’s fun stuff to play with. If you like that kind of thing.

  10. Wildride

    Don’t forget that its birthday only lasts 16 hours.

  11. To commemorate the occasion, here’s nine things about Neptune you may or may not know :

    1. Neptune’s core might well be a giant diamond.

    It was a study suggesting this that inspired Arthur C. Clarke to suggest the same idea for Jupiter in his ‘Space Odyssey’ SF series. Clarke himself wrote :

    “The startling idea that gas giants might have diamond cores has been seriously put forward by M. Ross and F. Ree of the Lawrence Livermore laboratory, University of California, for the cases of Uranus and Neptune. It seems to me that anything they can do, Jupiter could do better, DeBeers shareholders please note.”
    (Page 296, ‘2010: Odyssey Two’ Clarke, Grafton, 1983.)

    In actual fact, further study makes it seem unlikely the cores of “gas giants” Jupiter and Saturn are similar because they have different chemical composition and internal conditions to the “ice giants” Neptune & Uranus.

    2. Neptune is both larger and smaller than its planetary “twin” Uranus. It’s diameter is smaller than Uranus’ : 30,000 miles for Neptune versus 32,000 miles for Uranus. However, Neptune is much denser and thus larger in mass – it would take 17 Earths to match Neptune’s mass but only 14 Earths to match Uranus’ mass.

    3. Neptune which is named for the Roman god of the sea has no oceans – yet. But it may develop an ocean after the Sun’s death in 8 billion years time.

    From Ken Croswell’s online article – “No Ocean on Neptune – Yet.” : http://kencroswell.com/NeptuneOcean.html

    4. Neptune may have up to twenty times as many Trojan asteroids sharing its orbit as Jupiter according to a study by Scott Sheppard of the Carnegie Institution of Washington and Chadwick Trujillo of the Gemini Observatory in Hawaii using the 6.5-meter Magellan telescope in Chile. D.

    Source : D. Powell, “Neptune may have thousands of Escorts”, Space.com online news item, 30th January 2007. See :

    http://www.space.com/scienceastronomy/070130_st_neptune_trojans.html

    5. The first person to propose the existence of Neptune was Rev. T.J. Hussey in 1834. He was the first of several individuals (incl. later most famously J.C. Adams & U.J.J. LeVerrier in 1845) to suggest that an unknown planet is responsible for Uranus’ orbital “misbehaviour.” Uranus known since Herschel’s discovery in 1781 had been refusing to follow its predicted path sometimes moving ahead of schedule, other times falling behind. It wasn’t until Sept. 23rd 1846 that Neptune was finally discovered.

    Source : Page 54, ‘The Neptune File’ Tom Standage, Penguin group, 2000 & P. 170, Moore, ‘New Guide to the Planets’, Sidgwick & Jackson, 1993.

    6. Neptune has the clumpiest rings of any of the ringed planet and, for a time, (pre-Voyager II, 1989) Neptune was thought to have only ring arcs rather than complete rings.

    7. Neptune’s Great Dark Spot storm seen in dramatic detail by Voyager II in has since vanished as observed in later images by the Hubble Space telescope. Wonder if it appears and disappears every Neptunean year at some stage?

    8. Nereid, one of Neptune’s outermost moons has the most eccentric orbit of any moon in our solar system. Nereid takes 360 days (very nearly a full earth year orbiting the Sun)to complete its strange orbit which takes it from 1.3 to 9.6 million km from Neptune. Moreover, another outer Neptunean moon named Halimede may be a fragment of Nereid which was broken off in a huge collision.

    Source : Wikipedia respective pages for Nereid and Halimede.

    & one last Neptune fact – to end on a happy note! ;-)

    9. Despite the major controversy following the discovery of Neptune had been over competing independent predictions by French astronomer Urbain Jean Joseph Le Verrier and British astronomer John Couch Adams these two men, Adams and LeVerrier meet for each other in June 1847, and – despite all the controversy over Neptune’s discovery – became life-long friends.

    So there you go. Almost a top ten list and its almost time for the Letterman show now too! ;-)

    HAPPY NEPTUNEAN NEW YEAR Y’all! :-D

  12. So imagine you were at the center of the Sun (wearing sunblock 10^12) in 1846

    So, what you’re saying is that you wouldn’t get a tan prior to being incinerated?

    On Neptune, I’d only be a little over 3 months old.

    So, where’s your post on “how long is a ‘month’”? :-)

    Triton takes only 5.877 Earth days to complete an orbit, so a Neptunian year has over 10,240 “months”, not 12. That makes you over 2,500 months old!

    Bismillach, NO!

    I had to read a few paragraphs before I got that one. Nice semi-obscure reference.

    I’m going to sit back and eat a Krabby Patty

    Please tell me that the little BA isn’t into SpongeBob. Isn’t she too old for that? Though I hate to admit that yesterday, I asked our 14-year-old where “double, double, toil and trouble” comes from (I forget how the line came up in conversation), and he said he knew the answer because he saw it on SpongeBob.

  13. Ha ha. You said Ouranos.

    … Unfulfilling…

  14. Messier Tidy Upper:
    spacecraft have not yet captured a “true” or “natural” image of Neptune. Voyager’s camera was only sensitive out to the orange end of the spectrum, and used orange filters in lieu of red. So it’s color is an approximation on those famous images like at the top of this fine article. Hubble shoots Neptune in near-infrared light where some cloud features become visible. In an eyepiece on a large telescope, the planet often appears dusky-blue to me; not very colorful, but blue nonetheless. Definitely not the vivid blue in the voyager photos.

  15. Chris A.

    [grammatical nitpick]
    “The effect is small, but measurable, and in fact it was Neptune’s affect on Uranus that allowed astronomers to find it in the first place!”

    Phil, it should be “effect” both times in this sentence.
    [/grammatical nitpick]

  16. Grand Lunar

    Regardless of the exact moment, Neptune still is a cool place (and not just in the obvious manner either).

    “I think what’s most frightening about all this is that I understand it.”

    That’s why you have the PhD, Phil!

  17. Cynthia

    That is one long year lol

  18. Timmy

    I’m still confused. My party invitation said “tomorrow at 12″… Is that 12 noon today or midnight yesterday? Did I miss the cake?

  19. AJKamper

    Darnit, Ken B beat me to my point. But okay, still, Happy Birthday, Neptune. I’m going to celebrate with a drink of water in honor of its namesake.

  20. Doug

    @Messier Tidy Upper:

    Wikipedia has the albedo for the planets, both Bond albedo and Geometric:
    http://en.wikipedia.org/wiki/Geometric_albedo

    Neptune and Uranus are somewhat similar, compared to other objects in the solar system. However, Neptune does have the lowest albedo of the gas giants. Mercury, Earth, and Mars have even lower albedo. But it also seems that Neptune’s albedo changes significantly with time.

    However, when it comes to temperature, I think internal heat plays more of a factor than distance to the sun and albedo. The real unknown is what is causing the heating in the first place (my bet is on radioactive decay).

    I really hope we send a Cassini-like orbiter to Neptune sometime soon, but there don’t seem to be any plans to do that right now.

  21. Rebecca Harbison

    MTU:

    Also, albedo is subjective when measured by our eyes: consider how bright the Moon looks from Earth, while when spacecraft happen to see the Moon and the Earth in the same frame, the Moon is clearly dark gray. Neptune also gets less Sun than Uranus does, by virtue of it being further out, so there’s less to reflect — it doesn’t affect the actual albedo, but would affect a brightness measurement. (If a human were out at Neptune, though, his or her eyes would probably adapt.)

    Google tells me that Neptune’s albedo is about 0.4, which is comparable to Earth’s*. Mercury’s is 0.14, so it would be much darker, if you could somehow place them side-by-side. Uranus’s is a bit more reflective (at 0.5), though.

    * But probably more uniform, given Earth doesn’t have a global cloud layer.

  22. Sam H

    About all these comments on Neptune’s true colour and albedo: If we were floating in the Neptune system, exactly how bright would the sun, moons and the planet itself be to human eyes? The Voyager photos are obviously brightened (although I never knew they weren’t true colour), so it being dimmer out there would human eyes see as much detail, especially in the case of a major storm such as the Great Dark Spot and the associated white high-altitude clouds? Would the colour differences be more subdued to our eyes? And how about the distant sun? I understand that it would appear as a point, but would it still be too bright to look at? Say, as bright as an arc lamp or an epic flashlight? And how ’bout them moons? I’m assuming that the inner moons would appear as VERY faint stars from a distance if you could see them at all (Nereid would probably be invisible if it was anywhere farther away than perigee), but as for Triton – would all that frozen NO₂ boost the moon’s albedo?

    /end question rant. And @12 Ken B: On the verge of 17, I can still find SpongeBob quite amusing in its own campy way at times. To some extent you could say it’s the Looney Tunes of our generation (and I’m pretty sure most of that generation are still amused by it even today :) )

  23. TDL

    @Phil
    “On Neptune, I’d only be a little over 3 months old. ”

    On Earth a month is defined roughly by the period for one orbit of our moon around our planet, so on Neptune we would need to consider the orbit of a moon around Neptune…there are thirteen known moons of Neptune, so….oh crap! :)

  24. Gwif

    So when do we get to celebrate Pluto’s birthday?

  25. So how many candles should I put on Neptune’s cake? One, or a 165?

  26. Sam H: “If we were floating in the Neptune system, exactly how bright would the sun, moons and the planet itself be to human eyes?”

    Sun would be magnitude -19.3, according to Wikipedia, which is 900 times dimmer than the Sun viewed from Earth, but 420 times brighter than our full moon. It would be perhaps twice the angular diameter of Jupiter as viewed from Earth, so probably unrecognizable as a disk. I suspect a point of that kind of intensity would be very uncomfortable to look at.

    Triton, however, despite being a similar distance away to our moon and a similar size, would be very dim, with a magnitude of around +3. (It may be the only moon visible to human eyes, with the possible exception of Proteus.)

    All assuming you’re on the surface of Neptune and able to see clearly through to space, of course…

  27. MattF

    Gwif: So when do we get to celebrate Pluto’s birthday?

    2178.

  28. Gwif:

    So when do we get to celebrate Pluto’s birthday?

    I don’t know. I’ll have to ask Mickey.
    <GDRFC>

  29. Sam H

    @27
    Bob D: Thanks for that :) . It must be really dim out there, and frozen NO2 is darker than I thought…
    How about the planet itself? If it’s that dim would be able to see much detail at all?

  30. Neil NZ

    In New Zealand the date and time is 6:38AM, July 13.

  31. I came across the anecdote about Galileo seeing Neptune just recently, when I was researching for my upcoming episode of 365 Days of Astronomy (which airs on August 14). I put it in, unaware that everyone would be talking about it in the intervening month.

    Pretty confident you’ll enjoy my episode (it’s got planets in it, surely that’s enough) and am excited about it. Boils down to solar system fundamentals as told by someone who’s not at all accustomed to speaking into a microphone, but lots of fun, especially the thought experiment about dropping the earth into Jupiter. (Spoiler: it breaks apart under tidal forces and looks spectacular.)

  32. @14. Sean :

    Messier Tidy Upper: spacecraft have not yet captured a “true” or “natural” image of Neptune. Voyager’s camera was only sensitive out to the orange end of the spectrum, and used orange filters in lieu of red. So it’s color is an approximation on those famous images like at the top of this fine article. Hubble shoots Neptune in near-infrared light where some cloud features become visible. In an eyepiece on a large telescope, the planet often appears dusky-blue to me; not very colorful, but blue nonetheless. Definitely not the vivid blue in the voyager photos.

    Thanks I didn’t realise that. Must admit I always thought those were pretty much true colour, as we’d see them unaided eye images. :-)

    @ 21. Rebecca Harbison :

    MTU:

    Also, albedo is subjective when measured by our eyes ..[Snip] .. Neptune also gets less Sun than Uranus does, by virtue of it being further out, so there’s less to reflect — it doesn’t affect the actual albedo, but would affect a brightness measurement. (If a human were out at Neptune, though, his or her eyes would probably adapt.) Google tells me that Neptune’s albedo is about 0.4, which is comparable to Earth’s. Mercury’s is 0.14, so it would be much darker, if you could somehow place them side-by-side. Uranus’s is a bit more reflective (at 0.5), though.

    &

    @20. Doug :

    @Messier Tidy Upper: Wikipedia has the albedo for the planets, both Bond albedo and Geometric .. [snip] .. Neptune and Uranus are somewhat similar, compared to other objects in the solar system. However, Neptune does have the lowest albedo of the gas giants. Mercury, Earth, and Mars have even lower albedo. But it also seems that Neptune’s albedo changes significantly with time.

    My thanks go to both of you as well. Much appreciated. :-)

  33. @31. Ken B :

    Gwif: “So when do we get to celebrate Pluto’s birthday?”
    I don’t know. I’ll have to ask Mickey.

    GDRFC = ??? [Puzzled & curious.]

    To answer the original question as asked by (# 25.) Gwif : Pluto was discovered by Clyde Tombaugh in 1930 – Feb. 18th – and takes 248.09 years to complete one orbit. So rounding that figure up to 249 earth years [taps away on calculator] that would be about the year 2179. :-)

    EDIT : Ah, I see (#29.) MattF has given a similar answer too.

  34. Ian

    You say “Neptune was discovered on September 23, 1846 by astronomer Johann Galle using star charts by Johann Encke, and they are generally given credit for it.”

    The version I know is that Urbain Le Verrier of France and John Couch Adams of England, who were mathematicians and astronomers, independently predicted the location of the planet by measuring how the gravity of a hypothetical unseen object could affect Uranus’s path.

    Le Verrier sent a note describing his predicted location of the new planet to the German astronomer Johann Gottfried Galle at the Berlin Observatory. Over the course of two nights in 1846, Galle found and identified Neptune as a planet, less than a degree from Le Verrier’s predicted position.

  35. Svlad Cjelli

    Happy new year! =D

  36. Captn Tommy

    Who is Bary? And what does he have to do with the center of mass?

  37. DigitalAxis

    @KenB:

    5.9 days, and BACKWARDS. I love Triton, the cantaloupe world. We really need to send a Cassini-style orbiter out there. We really need something more powerful than a radiothermal generator to power it, though.

  38. smitty

    “On Neptune, I’d only be a little over 3 months old. ”

    But a Neptunian “month” would be based on Triton’s orbit! More math needed.

  39. Goodcarver

    Beautiful! So much so that it has become my Desktop background for the present.

  40. Matt B.

    If we’d been able to send a probe to Neptune on the day it was discovered, it would be done with its parallax survey now, in which a “parsec” equals 99.91 (~100) c-yrs.

    And since Uranus takes half as long to orbit the Sun, it should also be in approximately the same place it was when Neptune was discovered.

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