by Jeff Barbour
It was stuck in my brain. Yep, right there somewhere between the frontal and left temporal lobes. Of course, Saturday night was SCAC star party night. Why after all, the Moon wouldn't rise until after 3am. Right?
Wrong.
But just because there's no star party doesn't mean you don't have to go observing. And just because there's no star party doesn't mean you have to observe alone. It was Dan who did the research and alerted me to the realities of the situation. So it was Dan who accompanied Argo and me up to China Ridge for a little star gazing. It was also Dan who brought along his accessory case - filled with all kinds of goodies. A fine Takahashi prism diagonal. (Yes, there are such things!) And that 7mm Radian and 85 degree apparent FOV 17mm Nagler.
And Argo likes them accessories very much thank you!
We arrived on site about 8:00. Picked a different turn out on Big Basin Highway than the usual. Had a bit of trouble catching a descending Jupiter. (Needed to position Argo strategically to peerk through a "foliage gap" in a tree to the west.) Seeing stability, typical of China Ridge, was 6/10. Argo experienced the usual "travel-lag" (in the form of tube currents). Even so, the sky would occasionally stabilize and the 7mm revealed a temporary 7/10 view of Jupe's cloudtops. But we didn't dwell on His Royal Not-So-Highness-Anymore.
Venus far outshone Jupiter. Unlike the half-dozen other views of the planet these last few weeks, considerable atmo-chromaticism was visible. No way to achieve any kind of edge-focus. Aphrodite after an Olympian night of partying! Give her time, once she looses most of her extra-bulk and gains some elongation - why maybe we'll even catch her blush (in the form of that ashen glow)!
Skydark now takes its time. Dan and I could only be out till 10:30. Things didn't really darken enough for deepsky until after 9:00. Several bright stars took up residence early on though. We turned Argo on Arcturus and star tested a bit. The extrafocal image showed that classic "plume" of tube currents. More sky instability was visible extra-focally than intra-focal. (Cause you actually focus more on the sky itself that side of focus.)
Dan and I chatted about fresnel ring structures and effects of central obstruction. We conceptualized that the obstruction causes a slight phase-shift in a minority of the stars photons. If the quantity of such phase-shifts increases (past a certain point) a "de-inforcement" of neighboring - non-diffracted - photons occurs. Thus a loss of contrast. Of course, this also means a reinforcement of photons comprising diffraction rings. Since we had both recently seen Iota Leonis through an AP155 APO (non-obstructed), the effect was rather vividly exemplified by turningd Argo on that same binary. (Yep, the only way to minimize the effect of that pesky first diffract is to boost the magnification up to say 400x. In so doing, the ring's average surface brightness would diminish. This would allow the secondary's airy disk to reveal itself in all its coy beauty.)
Dan and I didn't run up the magnification. (Read this as "Argo really liked that Radian"!). Instead we dropped in the Nagler and got sucked into that huge 45 arcmin 105x field of view - wow!) Corvus stood right there to the south so we took an early evening peek at:
Planetary Nebula NGC 4361 Magnitude: 10.00v, Size: 1.8 RA: 12h 24m, Dec: 18d 48m S Threshold Scope Size: 88mm, Optimum Scope Size: 220mm, Recommended Magnification: 134x Average Surface Brightness at
At the time of this viewing we held stars down to about magnitude 4.5 (local to Corvus). Under 5/10 seeing (of that same locale) the 105x calculated threshold limiting magnitude at (for 150mm Argo) comes out to about 11.7. Based on this - and the planetary's ASB, you wouldn't expect much of a view. In fact Dan (whose eyesight is sharper than mine, but is slightly less sensitive to light) felt it was an accomplishment just to locate the planetary. Meanwhile, I was unable to clearly make our a frontier to this "face on galaxy look-a-like". But internally (under moderate aversion) I could detect a central star and see a distinct brightening to the core. - Nothing "annular" about this baby!
Now as much as I might like to detail the rest of the evening's views, time is short for me this fine Sunday afternoon. Suffice to say, we payed respects to the Ghost of Jupiter planetary in Hydra (intensely bright and colorific - handles all the magnification the sky permits), tripped to a number of showcase galaxies (Sombrero, NGC 4565, M81 and M82). Pondered resolution of a trio of well-positioned globular clusters (M's53, 3 and 13). And finally got a uninspiring view of a faint glow well south of Spica hanging just above the western ridge...
And as for the virtues of a fine set of accessories: Had no difficulty holding the 12.7 magnitude star direct in M44 at 105x through 5.3 ULM skies. - Effectively the combination of Takahashi diagonal and Nagler eyepiece added maybe 4/10ths of a magnitude to Argos reach (under similar circumstances to that using my less expensive Vixen mirror diagonal and 15mm Ultrascopic).
So forget more aperture for this Jeff person. Got to start saving up for some super-fine accessories!