John Pazmino
 NYSkies Astronomy Inc
 2009 January 2 
    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. 
    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 
    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.
    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 
    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 
    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 
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. 
    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.