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Robert Tulip
2009-Apr-19, 12:34 AM
Neptune (http://en.wikipedia.org/wiki/Neptune) was discovered on 23 September 1846 and has orbital period of 60,190 days = 164.79 years. Neptune will return to its sidereal discovery point on about 10 July 2011 (not sure if this date is exact).

The Neptune return point can be considered against the tropical zodiac as well as against sidereal position. Tropically, Neptune was at 25°54 Aquarius on the date of its discovery, and returned to this position last week, on 12 April 2009, entering its second tropical orbit since human discovery.

This 2.25 year difference between sidereal and tropical return dates is a function of the precession of the equinox.

slang
2009-Apr-19, 10:08 PM
Sounds like a great reason for a party!

It does make one pause and think about the enormity of just our dinky little solar system though. Terms like "our neighbor planet"... are you kidding?!

"Space is big. Really big. You just won't believe how vastly hugely mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space." -- Douglas Noel Adams

*grabs towel and tries not to panic*

George
2009-Apr-19, 11:51 PM
Wow, most my years have seemed shorter and shorter. Nice to have one that has taken a while. ;)

George
2009-Apr-20, 12:07 AM
Neptune (http://en.wikipedia.org/wiki/Neptune) was discovered on 23 September 1846 and has orbital period of 60,190 days = 164.79 years. Neptune will return to its sidereal discovery point on about 10 July 2011 (not sure if this date is exact). This checks with my Quatro Pro date function calculator.


This 2.25 year difference between sidereal and tropical return dates is a function of the precession of the equinox. I don't understand how it could be off that much. :doh:

tony873004
2009-Apr-20, 01:09 AM
This is interesting. If you use the formula P=2*pi*sqrt(a^3/GM) to compute Neptune's period, using Neptune's published SMA for a, it differs by about 100 days from its published period. I even added the mass of all the planets to the sun for a more accurate result, but I'm still off by about 100 days. I wonder if it's published period is time averaged, and compensates for the small oscillations in its SMA?

I've added 1 Neptune year to my birthday calculator (using the published value for Neptune's period). Enter Neptune's discovery date of 23 September 1846, and it tells you that 1 Neptune year will happen on July 9, 2011.
http://orbitsimulator.com/birthday/b8.html
You can use this calculator to find your Jovian birthdays too, as well as lots of other overlooked milestones.

The value on Nasa's web page differs by Wikipedia's value by 1 day. Wikipedia's value would give July 10, 2011.
http://nssdc.gsfc.nasa.gov/planetary/factsheet/neptunefact.html

Hornblower
2009-Apr-20, 01:13 AM
Neptune (http://en.wikipedia.org/wiki/Neptune) was discovered on 23 September 1846 and has orbital period of 60,190 days = 164.79 years. Neptune will return to its sidereal discovery point on about 10 July 2011 (not sure if this date is exact).

The Neptune return point can be considered against the tropical zodiac as well as against sidereal position. Tropically, Neptune was at 25°54 Aquarius on the date of its discovery, and returned to this position last week, on 12 April 2009, entering its second tropical orbit since human discovery.

This 2.25 year difference between sidereal and tropical return dates is a function of the precession of the equinox.I think you miscalculated. I get about 1.05 year for the difference.

Using round numbers for illustration, the equinox point moves about 165/25,800 of the way around the ecliptic. Multiply that by 165 years and we get the approximate time to subtract from Neptune's siderial period.

To get a really accurate result, use the best available numbers and set up a pair of simultaneous equations to find where Neptune and the precessing point meet.

Robert Tulip
2009-Apr-20, 02:12 AM
When I said the difference was due to precession, I should have added that it is also due to the geocentric frame of reference of the tropical ephemeris, with retrograde motion etc. The 2.25 year difference is correct, as Neptune actually did reach its tropical discovery point last week.

Tropical charts http://www.astro.com/swisseph/ae/1800/ae_1846.pdf and http://www.astro.com/swisseph/ae/2000/ae_2009.pdf show Neptune was retrograde at the time of its discovery and is now moving forward.

Hornblower
2009-Apr-20, 11:38 AM
To get a really accurate result, use the best available numbers and set up a pair of simultaneous equations to find where Neptune and the precessing point meet.

Let me back off of this one. It is not that simple unless the orbit is perfectly circular.

Robert Tulip
2009-Apr-20, 11:55 PM
Sounds like a great reason for a party!

It does make one pause and think about the enormity of just our dinky little solar system though. Terms like "our neighbor planet"... are you kidding?!

"Space is big. Really big. You just won't believe how vastly hugely mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space." -- Douglas Noel Adams

*grabs towel and tries not to panic*

Yes, space is enormous, but the Neptune orbital period of 164.79 years and orbital diameter of nine billion kilometres are short and small by astronomical scales. Neptune has orbited the sun more than twenty four million times in the four billion years since life evolved on earth. You would need to travel more than one thousand Neptune orbit diameters to reach the nearest star four light years away.


Let me back off of this one. It is not that simple unless the orbit is perfectly circular.
Neptune’s orbital eccentricity is only 0.1%, so ellipticity is not going to make a big difference to the calculation of precession date

tracer
2009-Apr-21, 02:48 AM
Yes, space is enormous, but the Neptune orbital period of 164.79 years and orbital diameter of nine billion kilometres are short and small by astronomical scales.

It's still big enough to beat up your older brother, though.

Robert Tulip
2009-Apr-21, 05:05 AM
I think you miscalculated. I get about 1.05 year for the difference.

Using round numbers for illustration, the equinox point moves about 165/25,800 of the way around the ecliptic. Multiply that by 165 years and we get the approximate time to subtract from Neptune's siderial period.

To get a really accurate result, use the best available numbers and set up a pair of simultaneous equations to find where Neptune and the precessing point meet. The 1.05 year figure on precession gives a precessed return date of 20 June 2010. It seems the 2.25 year difference between the sidereal date of 10 July 2011 and the observed tropical date of 12 April 2009 is 47% precession and 53% effects of apparent retrograde motion. Neptune stations on its tropical discovery point of 25°55 Aquarius for two weeks in November 2010. It is now fairly easy to find in the night sky right next to Jupiter, which is conjunct Neptune for the three months of May-July 2009.

jlhredshift
2009-Apr-21, 11:04 AM
I suppose you are all using calculators.



John Couch Adams was born in Cornwall, England in 1819 to a farming family. From a very early age he amazed everyone with his extraordinary abilities to do mathematical calculations in his head without the use of pen and paper. He was educated in mathematics at St. Johns College, Cambridge. While still an undergraduate, he performed an investigation to try to explain the reason for the irregularities in the motion of the planet Uranus. Adams theorized that the unexpected planetary orbit could be due to the presence of an as yet undiscovered planet in the vicinity. Adams theorized that the new planet was twice as far from the Sun as Uranus. All of the calculations were worked out in his head before he ever wrote them down. Once Adams did put his work on paper, he submitted it to the director of the Cambridge Observatory. The observatory took no action on his work. Several months later, Urbain Le Verrier submitted similar work to Johann Gottfried Galle, the director of the Berlin Observatory. Galle acted on Le Verrier's work and became the first person to observe Neptune. After the discovery of Neptune, the director of the Cambridge Observatory pointed out that John Couch Adams had been the first to predict the presence of Neptune. Le Verrier resented the effort to have Adams declared the sole discoverer of Neptune. Adams, a quiet, unambitious man was content to share the credit.

My Bold.

But, that's OK, Adams didn't have one.

From NASA Starchild (http://starchild.gsfc.nasa.gov/docs/StarChild/whos_who_level2/adams.html)

Robert Tulip
2009-Apr-21, 08:05 PM
John Couch Adams ...to try to explain the reason for the irregularities in the motion of the planet Uranus. Adams theorized that the unexpected planetary orbit could be due to the presence of an as yet undiscovered planet in the vicinity. Adams theorized that the new planet was twice as far from the Sun as Uranus. All of the calculations were worked out in his head before he ever wrote them down.From NASA Starchild (http://starchild.gsfc.nasa.gov/docs/StarChild/whos_who_level2/adams.html)Thanks. You are right that you need to conceptualise what you want to find out before working it out. In further pondering this issue, the question arises of exactly when Neptune will reach the position in the sky where it was when Le Verrier first set eyes on it. For this calculation, we need to correct the tropical ephemeris for precession. At discovery on 23/9/1846, Neptune was at tropical 25°55 Aquarius. This point has shifted by 164.79/25765 = 0.64% = 2.3 degrees of arc since then. Hence the equivalent point today to Neptune’s discovery point is tropical 28°37 Aquarius, which Neptune will reach on Friday 14 May 2010.

Plutocrat
2009-May-04, 12:40 AM
A footnote to this discussion:

Some books incorrectly state that Percival Lowell used deviations in Neptune's orbit to pinpoint Pluto's location. But he couldn't, for exactly the reason stated here: Neptune had not yet completed a full orbit around the Sun since its discovery; thus, its precise orbit was not known.

Instead, Lowell had to use Uranus, which was discovered in 1781 and first seen in 1690, and whose orbital period is only 84 years.

StupendousMan
2009-May-04, 06:30 PM
A footnote to this discussion:

Some books incorrectly state that Percival Lowell used deviations in Neptune's orbit to pinpoint Pluto's location. But he couldn't, for exactly the reason stated here: Neptune had not yet completed a full orbit around the Sun since its discovery; thus, its precise orbit was not known.

Instead, Lowell had to use Uranus, which was discovered in 1781 and first seen in 1690, and whose orbital period is only 84 years.

True. But it was a close thing: as the first few decades of the twentieth century passed, the orbit of Neptune became better and better measured. In 1919, W. H. Pickering published a paper in which he attempted to use perturbations to the orbit of Neptune -- not Uranus -- to derive the position of the presumed outer planet. See

W. H. Pickering, "Perturbation of Neptune," Harvard College Observatory Circulars, vol 215, pp. 1-2 (1919).

http://adsabs.harvard.edu/abs/1919HarCi.215....1P

Doodler
2009-May-07, 02:23 PM
Neptune has orbited the sun more than twenty four million times in the four billion years since life evolved on earth.

Might be less than that. I seem to recall a paper a while back postulating that Neptune and Uranus might have flip flopped orbits a while back when the solar system was settling down.

Robert Tulip
2009-May-08, 05:16 AM
Might be less than that. I seem to recall a paper a while back postulating that Neptune and Uranus might have flip flopped orbits a while back when the solar system was settling down.Yes, the paper was discussed on BAUT with regard to the impact on the early earth and moon. http://www.bautforum.com/astronomy/67975-uranus-neptune-switched-places.html

But if Neptune used to be closer, surely it would have been going faster, and it would have orbited the sun more times rather than less?

Doodler
2009-May-10, 12:58 PM
You're right, got'em backwards...my fault.

Robert Tulip
2009-May-13, 04:54 AM
The graphic of Neptune and Uranus switching places is at http://www.psrd.hawaii.edu/WebImg/LHB-sim-small.gif

Looks like a good model for the history of the solar system.

After busting the ring of planetesimals in the cataclysm of the early bombardment, Neptune settled down into a nice regular orbit. Just very slow from our point of view.

Robert Tulip
2009-Jun-03, 03:16 AM
A friend sent me the attached pictures of the position of Neptune from the Starry Night website. They are a pair of simple diagrams comparing what Urbain le Verrier would have seen through his telescope on September 23rd, 1846 with what we will see as Neptune completes one full orbit since its discovery, said here to be on February 11th, 2011, although Neptune completes its orbital period on 10 July 2011.

The diagonal line is the plane of the earth's orbit which is markedly different in each image because it's a different time of year and in the 2011 image the Sun is there. The return date, time and position may have been calculated to factor in the retrograde and forward movements of Neptune.