Star Points for June, 2002; by Curtis Roelle
Modern Dance of the Classical Planets Continues


June and July continue as busy months for our neighboring worlds. 
The same five naked eye planets that entertained us with their
western waltz in the evening twilight in April and May during their
celestial roundup continue their dance while conjugating in pairs
thee times in a one month period between June 3 and July 3.

During each pairing, or conjunction, the participating planets will
be at closest apparent proximity to each another on some specific
date.  However, to fully appreciate a conjunction one should keep
an eye out on consecutive evenings, or mornings as the case may be,
as they draw closer and closer together.

Conjunctions require no optical equipment to be enjoyed.  They are
the kind of event whose sublime beauty has captured the
appreciative eye as long as people have been walking on the earth.

The naked eye is all that you need, although a pair of binoculars
may help pick out the fainter planets in bright twilight.  A small
or medium sized telescope will also resolve the planets into round
discs, and may reveal the phases of the inner planets Venus and
Mercury.

The first, and grandest of the triple conjunction involves the two
brightest planets - the King and Queen - Jupiter and Venus.  The
royal couple will be only 1.6 degrees apart in the evening twilight
on Monday, June 3.  By 9:00 p.m. EDT the planets are unmistakable
as they hover brightly low in the western sky 20 degrees above the
horizon.  

You may recall that 10 degrees is the apparent width of your fist
at the end of an outstretched arm.  Therefore the planetary pair is
two fists above the horizon.

Venus is the brighter one.  Jupiter will be to its lower left.  If
you looked the night before before on Sunday you would have noticed
that Venus was below Jupiter.  

Both planets are on the opposite side of the sun from us at this
time.  However, in a small telescope you might be able to discern
Venus' gibbous phase.  Venus' disc appears a little less than full.

As you keep watch over the next several nights observe how the
planets begin to separate with Venus appearing to move higher.  You
may be impressed by the detectable motion.

But actually, it isn't so much that Venus is rising, but rather
Jupiter is sinking.  One of the motions acting against Jupiter is
the earth's orbital motion around the sun which causes the stars to
set approximately four minutes earlier each night.  This motion
causes Jupiter to "slip" along with the stars.  
Although Venus is progressing eastward, the westward slip due to
orbital motion give the illusion that Venus is standing still night
after night with respect to the horizon.  Indeed, over the next
several nights Venus will be at the same altitude above the horizon
as it was at the same time the night before. 

It's like watching a dog swimming upstream against the current. 
It's head appears motionless bobbing in the water.

Keep your eye on Jupiter.  Jupiter has another evening encounter
with a different planet coming up in one month, as we'll see later.

Now something for the early risers.  The second conjunction,
between the ringed world Saturn and the innermost planet Mercury,
takes place on the morning of Tuesday, July 2.

At their closest the two planets are less than a quarter of a
degree apart.  In the morning twilight at 5:00 a.m. EDT the two
planets will be five degrees above the northeastern horizon.  Thus,
a horizon free of obstruction from trees, buildings, or hills is a
plus.

Both objects should be visible to the unaided eye and will be easy
targets in binoculars.  Due to their close proximity, they may also
be visible in the same eyepiece field at fairly high telescopic
magnifications. 

A telescope will easily show Saturn's rings.  However, they will be
distorted by earth's atmosphere due to Saturn's low elevation. 
High magnification might reveal Mercury's gibbous phase, but
atmospheric distortion will make telescopic observation difficult. 

Despite their apparent proximity in the sky, the closeness of the
pair is an optical illusion.  That morning Mercury is 77 million
miles from our planet.  However, Saturn lies another 831 million
miles beyond Mercury!  It is geometry that makes the two appear to
be close together in the sky.
 
Now, back to Jupiter which has changed partners.  On the following
evening Jupiter and Mars are in conjunction only 0.8 degree apart
on Wednesday, July 3.

Mars is quite a bit fainter than Jupiter.  According to Guy
Ottwell's astronomical calendar Jupiter will outshine Mars by a
factor of 27.5!  

You'll need a good unobstructed view of the northwestern horizon
since Jupiter is only about three degrees up in the evening
twilight at 9:00 p.m. EDT.  Sweeping the horizon with a pair of
binoculars will help spot the pair. 

Fainter Mars will be above and slightly to right of Jupiter. 
Because of their close apparent proximity both planets fit easily
into the same low power eyepiece field of a small telescope.
Hope that you've been enjoying the dance of the planets this
Spring.  I certainly have.  The next good conjunction will be Venus
and Mars in the morning sky in December.