JUPITER-NEPTUNE TRIPLE CONJUNCTION -------------------------------- John Pazmino NYSkies Astronomy Inc www.nyskies.org firstname.lastname@example.org 2009 January 2
Introduction ---------- The 2008 December 4 NYSkies Seminar discussed various conjunctions among planets, using the Moon-Jupiter-Venus convention as a starting point. One kind of conjunction I noted was a 'triple conjunction' when two planets, or a planet and star, conjunct three times within a few weeks or months. I recalled the triple conjunctions of Mars-Jupiter and Mars-Saturn in 1980-1981. I animated with my hands the movement of Mars relative to Jupiter or Saturn, then let the dialog move on to other aspects of planetary conjunctions. Discussion among NYSkiers since then pointed out the rarity of triple conjunctions and the chance to see one in 2009. This is the triple conjunction of Jupiter and Neptune in May, July, December 2009.
International Year of Astronomy ----------------------------- 2009 is International Year of Astronomy, promoted by IAU and UNESCO. During this year astronomers should show and explain certain concepts to the public, such as the rings of Saturn and the eclipse of epsilon Aurigae. There is an other, not well noted in IYA litterature, the triple conjunction of Jupiter with Neptune. This occurs in May, July, and December 2009 and should be an excellent chance to show this remote planet to the public. The first meet of Jupiter and Neptune occurs in the predawn sky, not convenient for most astronomers and hardly welcome for the lay person. The other two take place in evening thru night, one in the summer and one in the winter for seasonal variety. Neptune is the second of the telescopic planets and the first to be predicted based on Newton theory of gravity. Hence, showing and discussing Neptune can be a worthwhile addition to an IYA program. His proximity to Jupiter at and rear the conjunctions makes him easy to find. Should weather smother Neptune, Jupiter is usually still appreciable thru thin cloud.
Neptune ----- Any dialog about Neptune is going to drift into a debate about which planet in sequence he is, the last of eight or the eighth of nine. That is, is Pluto a planet or not? Pluto was deplanetized in 2006 by the IAU by a process still very much protested and substantially ignored among astronomers. Not with standing the prospect that there are other orbs in the outer solar system that may equal or excede Pluto in size or importance, there seems to be no valid cause to even bother with the Pluto deplanetization effort. As far as most astronomers care, Pluto is a planet and there can be new ones admitted to planet status in the future. Neptune is the eighth planet of the present nine in the solar system. If you got a large scope, more than 200mm aperture, you may show Pluto as an added treat during a summer starviewing session for the public. Pluto in July is in Sagittarius about 2-1/2 degree west of M24 open cluster. He is of magnitude 14. This part of the sky is in the Milky Way with hundreds of other 14th magnitude stars near Pluto! You need an accurate deep-magnitude chart to hunt up Pluto.
Triple conjunctions ----------------- A triple conjunction can take place only during the retrograde loop of a planet. An ecliptic longitude in the zone spanned by the retrograde loop is crossed three times. The first instance is when the planet is in prograde, eastward, direct motion before entering the loop. The second instance is when the planet is in westward, retrograde, motion within the loop. The third and last instance is when the planet is again in prograde motion after leaving the loop. Triple conjunctions are easiest to calculate against a star, whose longitude is fixed. Calculating a triple conjunction against an other planet is trickier because both planets are in their own loops. However, any good planetarium program can uncover the conjunctions by stepping thru days while watching the screen. A few can directly find conjunction thru a special dialog box. The dates turned up can be set in the planetarium for a visual check. It happens that Neptune, being so remote from Earth, has a small parallax effect and a small retrograde loop. As a first approximation you can treat neptune like a fixed star, with his location for mid year, and find when Jupiter crosses that longitude. You then swim around that date in the planetarium to hunt down the exact conjunction. Celestial almanacs list the planet conjunctions but few point out the triple character of the Jupiter-Neptune apparition. If you don't peruse the entire year and catch the three instances you may miss the show on one or an other date.
Longitude ------- Just about always an aspect of planets is computed relative to their ecliptic longitudes, not right ascension. You can use the latter method and get slightly different dates and separations. Both are perfectly valid methods but the longitude one is so prevalently intended that you may safely assume so unless purposely stated. Be aware that once in a while the assumption may prove wrong. The RASC Observer's Handbook, for example, uses right ascension for its planet-planet and planet-star computations. This is explained on page 20 of the 2009 edition. However, aspects of the planets relative to the Sun are based on longitude, not right ascension. The use of longitude rather than right ascension comes from the ease of working with longitude for planetary motions. Most algorithms are written for longitudes. It also makes better sense when banking planet locations and motion against the ecliptic. The conjunction occurs when the planets are abeam of each other, lined up orthogonally against the ecliptic. This article uses longitudes. The hour of geometric conjunction can differ slightly from other longitude-based sources because of the varying precision of algorithms used. These differences do not upset the value of the information presented here.
General situation --------------- Neptune during 2009 in is northeast Capricornus about 1/2 degree south of the ecliptic. The only considerable star nearby is mu Capricorni within a degree or so of each conjunction. For the instance on July 2009 mu is quite halfway between the planets, aiding in locating Neptune relative to Jupiter. The apparition evolves slowly, allowing substantially equivalent views of the conjunctions a couple days on either side of geometric conjunction. Altho Neptune is of 8th magnitude and can be lost in a sea of similarly dim stars, this part of the zodiac is star-poor. A detail chart of northeast Capricnrnus showing 9th magnitude stars will make Neptune obvious in the telescope field. Under 150 power the planet shows a tiny disc, like that of a Jupiter moon (close by for comparison). He may have a cyan or aqua tint, but not for sure. Color in faint celestial targets severely depends on the observer's vision. Only very large scopes will show Neptune's larger moon Triton. A detail finder chart done up for the day of observation is needed. There are no nearby deepsky objects. NGC7293 globular nebula is about 11 degrees southeast of Jupiter and M2 globular cluster is about 13 degrees north-northwest.
2009 May 27 --------- The geometric conjunction is on May 27 16h EDST. The closest visible approach is in the predawn hours of May 27. Neptune is 1/2 degree north of Jupiter. Here's the timetable of eventd for New York: --------------------- 2009 MAY 27, NEW YORK ---------------------- EDST | alt-az | event ------+--------+------ 00:00 | 14 98 | May 26->May 27 01:16 | 0 107 | Jupiter rises 04:16 | 27 141 | nautical dawn 04:56 | 32 152 | civil dawn 05:29 | 34 162 | sunrise 16:00 |-47 299 | geometric conjunction -------------------------------------- The altitude-azimuth are for Jupiter here and in the other timetables. This instance, the first of the triple conjunctions, is badly placed on the clock for most folk. Unless you're watching the May Aquarid meteor shower, there is little incentive to stage a Neptune watch.
2009 July 10 ---------- The geometric conjunction is on 2009 July 10 05h EDST. The planets are in the sky at nightfall being that both Jupiter and Neptune hit their oppositions in August. The closest approach is during the night of July 10-11. Neptune is 1/2 degree north of Jupiter. Here's the New York timetable ------------------------ 2009 JULY 9-10, NEW YORK ------------------------ EDST | alt-az | event ------+--------+------ 22:23 | 0 108 | Jupiter rises 00:00 | 15 125 | July 9->July 10 03:32 | 36 180 | Jupiter transits 04:20 | 36 193 | nautical dawn 05:00 | 32 204 | civil dawn 05:00 | 32 204 | geometric conjunction 05:33 | 29 213 | sunrise ------------------------ During this conjunction mu Capricorni is quite halfway between the planets. Some specs for the star: ---------------------------- Flamsteed | 51 Capricorni BSC, HR | 8351 Smithsonian | 164713 Henry Draper | 207958 Tycho | 5801-1017 Pos Pro Mot | 239478 Bonner Durch | BD-14:6149 R Asc (2000) | 21h 53m 18s decl (2000) | -13d 33m 06s app magn | +5.1 spectrum | F1-III distance | 106 LY ---------------------- This instance is the most favorable one for the public. It occurs in evening to midnight hours and there is a bright star to guide the viewer toward Neptune. Summer weather in New York can be brutally hot, hazy, humid. The discomfort factor may be excessive for most viewers. However, clear nights do occur. If the haze veils Neptune, Jupiter is the fallback target.
2009 Dec 21 --------- The lineup is on 2009 December 21 04h EST. The closest approach is in evening of the 20th. Neptune is 1/2 degree north of Jupiter. Here is the timetable for New York: -------------------------- 2009 DECEMBER 20, NEW YORK -------------------------- EST | alt-az | event ------+--------+------ 16:31 | 34 193 | sunset 17:02 | 32 205 | civil dusk 17:37 | 29 211 | nautical dusk 20:56 | 00 251 | Jupiter sets 00:00 |-34 282 | Dec 20->Dec 21 04:00 |-45 294 | geometric conjunction -------------------------------------- This conjunction is the most pleasant on the clock, in dusk and evening. You may have to wait for nautical dusk before Neptune resolves out of twilight. On the other hand, winter weather in New York can be cold and windy.
Conclusion -------- In June, Neptune is a bit West of Jupiter, still close enough for a skilled telescopist to jump off from Jupiter to him. From August thru November, Neptune is too far east of Jupiter to find easily. You better wait until December before Jupiter can be a jumpoff point to hunt up Neptune. Neptune-Jupiter triple conjunction in 2009 is a good chance to inspect the farther planet. You are guided by Jupiter and, for the July event, mu Capricorni. The lay person can view and examine Neptune more easily, can on his own point to Jupiter to recall where Neptune is, and better appreciate IYA thru an activity about the two planets.