Uranus and Neptune: same altitude before dawn

Event Date: July 11th
Time: 3:52(.34) AM

Brief

   Uranus and Neptune are now well placed shortly before the start of astronomical twilight.  Since Neptune is barely visible through most small telescopes at just slightly brighter than 8th magnitude, this is important to remember when trying to use a star field to find it.  Once we start to get too far into morning twilight, it is no longer visible, and Uranus (+5.8) disappears from our telescopes shortly after.  Even for nights that we have a dark enough sky to barely see Uranus with the unaided eye (unlike this morning with the Moon in the way), it is only a few arc-seconds in size, so difficult to see.  For this morning, I will show them at the same altitude at just under 41º, which I have done before.  The first image is a zoom-out of the two, while the second is a zoom-in (2x).  Both show the alt/az grid.  By looking at the second, we see that the two planets are precisely the same space between two of the gridlines.  Also, the image azimuth is close to  centered between them at azimuth 150º.

click on images to enlarge: courtesy of Starry Night Pro Plus, version 6.4.3, by Simulation Curriculum Corp.

Detailed

   Since the planets have moved a little further in prograde since I last showed this not long ago, the altitude value is slightly different.  Since then, Neptune has started retrograde, while Uranus is about to approach stationary a little later this week.  As a result of the timing and different movement of the two for some dates, there will be more slight variances in altitude over the next several months.  Also, Uranus is in a part of the sky for which it changes faster in declination; it is where the Sun is in early spring, when our days grow longer faster as a result of declination change for the Sun; that is a result of our tilt.  Each year this decade, as Uranus also increases faster in declination than Neptune, it also separates further from it.  Because of that, as the years continue to pass, there will be years for when Uranus is rising when Neptune is about to set.  They will not have another closest encounter with each other during our lifetime, as it will be the year 2165 when that happens!  Any humans still existing by then--if any at all--will see them at a spectacular 0.8º apart January of that year!  The last time that they were at their closest was not too long ago in comparison: late October of 1993.  Doing the math, given that Uranus has to catch up with Neptune with every revolution, that is almost 172 years between conjunctions, or a little more than twice the time it takes Uranus to revolve around the Sun.  Neptune's revolution is a little under 164 years, while Uranus' is short of 84 years.