JUPITER-NEPTUNE TRIPLE CONJUNCTION
--------------------------------
John Pazmino
NYSkies Astronomy Inc
www.nyskies.org
nyskies@nyskies.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.