Backyard, Boulder Creek

by Jeff Barbour

Observing conditions in the Santa Cruz Mountains are often quite variable. On better nights, skies as deep as magnitude 5.5 overhead are possible. Due to laminar air currents flowing off the Pacific Ocean (through mountain peaks and over passes populated by heat moderating redwoods) stability is often quite good as well.

Vexing the weather around here is the large amount of water vapor in the air. This water vapor often takes the form of fog settling in over the San Lorenzo River Valley - especially in the late Fall and Winter. Frequently, high thin clouds may spread across the sky. This is possible any time of year. And was the case last night.

A typical night of decent seeing allows me to hold stars direct overhead to about magnitude 5.2. Stability is generally 7/10. Through the 80mm achromat (affectionately know as "The Pup") such nights enable me to see those gorgeous little drops of starlight we optophiles call "airy disks". On the very best nights such airies (a diffraction phenomenon and not the orb of the star itself) are accompanied by one or more concentric "circles" of light termed "diffraction rings". When the rings go completely around (circumscribe) a stars airy disk, seeing is quite good (8/10). Should such a ring remain extremely still, the stability is even better - 9/10.

>From where I observe from such nights are very rare - I've had maybe three such nights over the last year and a half of observing. And they of course are spectacular - especially if accompanied by a sky of real depth!

Last nights sky was quite still - but not perfectly still - 8/10 still.

But last nights sky was also less than transparent - I could just hold 4.1 magnitude Mu Leonis direct.

Had the sky been a half magnitude deeper, I would have gone "deepskying". Instead I contented my observing eye with Jupiter, Saturn and a variety of double stars.

Last Sunday evening, the band I play jazz in was off (TAJQ). On that occasion what started as a long-overdue visit to China Ridge with 150mm MCT Argo turned into an oportunity to observe from fellow observer "El Marko's" favored observing site in Bonny Doon. Subsequently, the rest of the week was completely overcast. A planned trip to Fremont Peak with fellow SCAC astronomer Dan had to be postponed due to poor weather Saturday night. Sunday morning the sky was overcast when I set out for morning coffee. But within minutes of arrival at the coffee shop, son Eric and I pulled up chairs at a table drenched in late-morning sunshine. The day remained like that - even as I gathered guitar, amp, and microphone for the evening's musical adventures at the Brookdale Lodge Brookroom in rustic Brookdale California...

Earlier that day I received an email from El Marko, inviting me up to Bonny Doon where he would be observing that evening. Since I would be returning late from the gig, seized the opportunity to rquest that I NOT bring a scope (that way I could wrestle El Marko for views through that 12.5 inch dob!). Mark was to call me and leave a message if observing conditions supported our plan.

When I got home I could see that our plan would not pan out. Although Mark often gets clear skies at 2,500 feet when I am socked in down at 500, the clouds I saw looked pretty high. Checking email, I confirmed that El Marko's conditions were as poor as my own. - So out went the 80mm.

That first view of Jupiter confirmed the stability of the night sky. The four Galileans wer pinpricks against the grey haze that surrounded the planet. And at 140x, Jupe's limb was razor sharp. But detail was lacking.

There was just too much sky glow. Light that should have stayed put over the planet's cloudtops spilled everywhere. The result? Reduced contrast. Why it was tough enough even to make out the NEB!

Saturn is now very progressed to the west. At that hour (about 9:30) the planet lay some 30 degrees above the horizon. Even so Cassini could be (barely) resolved, but absolutley no sign of the SEB. Meanwhile, of the Saturnian satellites only Titan was detectable. Strangely, Cassini was more easily observed trailing the planet than leading it. The opposite of a pheneomenon I and others had noticed when resolving the Encke Minima with our 150mm Maks.

So with this initial view of the two gas giants behind me turned the Pup on Castor. Exquisite! Gorgeous airy disks (smaller/dimmer one trailing) colors pearly white with a hint of blue on the secondary. Gap between the pair larger than the airy disk of the primary. Then onto Theta Auriga. Caught a persistent brightening leading and to the south on the primary's single diffraction ring.

Back to Jupiter. One of the Galilean's seen moments before was MIA. And it was the one closest to the limb and overtaking it from the east. But no sign of it on the planets limb. Damnable skyglow was making detecting it impossible AND it would be an hour or so before the Galilean's shadow would take residence in the cloudtops. But wait. There's something else. A disturbance rotating in along the SEB...

Turned the Pup on Iota Leonis. Hoped to catch its sub-2 arcsec separated, disparate secondary. Nothing more than a faint brightening on the diffraction ring trailing and to the north. 140x. 220x. Nada.

Then onto to Xi Ursae Majoris. Superb, clean split at 140x. Two visibly unequal-sized airy disks with secondary leading. I thought of "El Marko". He and I had turned our "little 'uns" on this pair last year during an SCAC star party. I was using 120x, and had a very difficult time separating the pair. At 140x it was easy - and stunningly so. Even now 120x does not quite give thinline separation. Based on this, I've calculated the separation of this binary at about about 2.1 arc seconds. It may in fact be closing...

Not far from Xi UMA is 57. Though widish (5 arcsecs) this pair is quite disparate (mags 5.3 and 8.0). At best I detected a very faint presence south and slightly leading. Like most widish disparates, this was only feasible at lower magnifications - 80x.

Returning to Leo I located 90. Mildly disparate (mags 6.0 amd 7.3) the secondary could be held with slight aversion some 3 arcsecs southwest of the pinprick airy disk of the primary. Through a darker sky, this one should be obvious.

Completed my double-spree with glorious Gamma Leonis. An easy resolve at 80x, the stars in this widish pair showed unequal sized airy disks. In many ways Gamma reminds of Castor, but for being slightly dimmer and possessing a strong golden rather than pearlescent hue...

Before taking one last final view of a lowering Jupiter, dropped in on two galaxy pairs. M65 and 66 proved difficult to track down and completely lacked structure through 4.1 magnitude skies. While M81&82, were an easy locate and surprised me with a wee bit of structure. M81, showed considerable core concentration, and M82 a decent sense of frontier. The views of the galaxies were at 48x which easily encompasses both pairs and at an exit pupil of slightly less than 2mm which usually provides superb sky contrast on optimal (5.5) nights of transparency.

Meanwhile back at Jupiter, although the GRS could be vaguely seen transiting the central meridian, there was no sign of a shadow transit. Due to the low contrast, the GRS appeared as a rather ill-defined break in the normally continuous SEB.

I suppose I could have showed more patience, hung out for awhile and waited for that Galilean to show its "evil twin", but nah. Between some unusually excellent jazz, and poor skies I was ready to put an end of the day...

And of the night.

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