Salutations celestial sight seers!
I'm David Fuller, welcome to Eyes on the Sky; what's up this week?
“Arrr...
“X marks the spot” - now I just need me chart to find it.... ahoy there matey!
There she be.....”
This week the “Lunar X” will be visible to western Europe and the Americas.
This unique optical illusion occurs when sunlight grazes across the upper rims of the craters
Purbach, LaCailles and Blanchinus.
It isn't difficult to find, either – it just takes looking at the right time.
Invisible at 2100 hours UTC, it will pop into view an hour later, though it really is nicely
lit on the peaks with the black shadow below by 2300 hours.
This will be still in daylight for the U.S. at 7:00 pm EDT / 6 pm CDT, but no matter – as
you can see, the “X” can still be seen even in daylight.
If you can see the Moon, check out the X!
And it will be visible for another few hours, allowing the “X” shape to fade into a
darker sky even as it's revolution is altered slightly, pulling some of the lower detail
into view.
The view should be best around zero hour UTC, which is 7 PM EDT, 6 PM CDT.
But “X marks the spot” will remain in view for another hour or two afterwards.
ANY small telescope will reveal it to you – use about 100x magnification.
Dark Sky Fact: A sunset glow red-shifted light – this helps your body recognize night time.
But computer screens have blue shifted light – so download the free program f.lux to
automatically change your computer screen every day to red shift when the light outside
does, at sunset.
On April 16, 41 years ago, a Saturn 5 rocket launched Apollo 16 towards the Moon, and four
days later, John Young and Charles Duke became the ninth and tenth men to set foot on the
Moon's surface.
Visually from Earth, their landing site is not too far from the Lunar X, even though
the actual distance is some 400 miles away.
To find where they landed, look first for Sinus Asperitatis between Mare Tranquilitatis
and Mare Nectaris on the eastern portion of the Moon.
Early in the week on 16-th, the 100 km crater Theophilus is deeply shadowed, with 53 km
Beaumont below it to the south.
A day later, two companion craters, Cyrillus and Catharina, are nicely lit south of there.
And now we can look for the Apollo site too.
From Theophilus, scan west.
You'll see the “Lunar S” created by Mons Pench and the crater Kant named after German
philospher Immanuel Kant.
See the “S” laying on it's side?
Just to the west of that is the crater Descartes, named after the Frenchman philosopher Rene
Descartes.
Just north of there is a plain, and the Apollo landing site is approximately the same distance
from Descartes' northern wall as the crater is in diameter.
Just double the distance, and that's right about where Young and Duke were, 41 years
ago this week.
And given the philosopher craters in the area, perhaps that – and when humans may return
there - are good things to think about as you observe this area.
This area can be observed one to three days later as well, though the crater Descartes
becomes more difficult to identify by the weekend.
Observing tip: No neutral density filter yet?
No problem!
Reduce the Moon's comparative brilliance at the eyepiece by setting up NEAR some outdoor
lighting, which will keep your eyes from dark-adapting and avoiding them hurting while lunar observing.
Along The Ecliptic: Be sure to observe Jupiter in the west this week from one to two hours
after sunset, as it drops below 20 degrees of elevation after that time – BUT – spin
your scope east to locate Saturn 20 degrees up less than an hour later, over in the south-southeastern
sky.
That's all for this week.
Keep your eyes on the sky and your outdoor lights aimed down, so we can all see, what's
up.
I'm David Fuller, wishing you clear and dark skies.