27 june 2025, movement pairs

Seeing was not exceptional, but it was good enough to open the 20-inch and go after some movement pairs -- after what seems like a long while.  Got started at 10:00pm and finished at 12:30am.  Seeing did improve through the night, and it felt great to be out observing these pairs no one else tries to see.

HU  481 AB" 508; 847x: Exceptionally fine pair, 2 Dm, PA to the southwest.  SOC grade 3 orbit, 119.5-year period, it will widen slightly in the next 20 years but remain in the southwest.    

16h 21m 14.74s +22° 59' 18.8" P.A. 237.00 sep 0.5 mag 8.21,10.04 Sp F8 dist. 66.18 pc (215.88 l.y.)

KUI  66 AB: 508; 508x: 15 Boo.  Using an apodising mask and viewing through the peephole in my eyepiece cap, with seeing only, I see very small, faint point of light inside the first diffraction ring, ESE PA, closely separated. Interesting the B star has a 10th magnitude companion!  which I did not see, of course.

14h 14m 50.85s +10° 06' 02.2" P.A. 111.00 sep 0.8 mag 5.44,8.43 Sp K1III dist. 81.23 pc (264.97 l.y.)

KUI  79 AB: 508; 508x: Excellent, nicely split, faint, light red-orange stars, near equal, SSW PA.  Split with 282x but better seen 508x.  SOC grade 1 orbit, 12.955-year period (!), it will hang at this separation for a couple more years before diving to periastron, becoming detectible again after 2030.

17h 12m 07.78s +45° 39' 57.6" P.A. 289.00 sep 0.7 mag 10.02,10.25 Sp M3V dist. 5.98 pc (19.51 l.y.)

STF1865 AB: 508; 1693x: With apodising mask and peephole, all powers, elongated N-S.  SOC grade 2 orbit, 125.24-year period, it is coming off periastron now and will be resolvable in a couple years.  Struve was lucky to discover it at apastron. 

14h 41m 08.92s +13° 43' 42.0" P.A. 265.00 sep 0.1 mag 4.46,4.55 Sp A0V+A0V dist. 53.88 pc (175.76 l.y.)

STF1998 AB 508; 282x: Xi Sco.  Nice pair, equal white stars closely split, PA NE.  SOC grade 1 orbit, 45.9-year period, it will close and be due east by 2040.

16h 04m 22.13s -11° 22' 23.2" P.A. 12.00 sep 1.2 mag 4.84,4.86 Sp F5IV+F5IV

STT 341 AB: 508; 635x: Lovely light orange stars, 1Dm, nice separation, PA ESE.  SOC grade 2 orbit, it will head further SE until 2033 when it begins a rapid dive toward periastron, not resolvable again until the 2040s.

18h 05m 49.72s +21° 26' 45.6" P.A. 89.00 sep 0.452 mag 7.39,8.82 Sp G0V+G5V dist. 39.45 pc (128.69 l.y.)

17 june 2025

Hopefully our luck is changing weather-wise, as there have been several nights of at least clear skies.  Opened up the 20-inch in case seeing would cooperate, but it was poor at full aperture, so I masked down to 7-inches for the session.  I've run out of targets in the 13-15h range on the CDSA list, except for the closest splits which would require better seeing.  I'll spend some time learning how to use my Questar and trying to use the NV device on my 20-inch (more in-focus needed, so might need to rebuild the focuser board).

BU 1443 AB: 178; 140x: 3 Dm, very wide.  20% PRO, but a very wide 11,730 AU WS, 3.9+1.2 Msol, and RVD 5.6 > EV, it is not binary.

14h 30m 45.39s +04° 46' 20.2" P.A. 195.00 sep 55.7 mag 6.17,10.62 Sp gK4 dist. 212.77 pc (694.06 l.y.)

HLD  18 AB: 178; 280x: 3 Dm, difficult, can just detect B with direct vision, close to A, need magnification to separate. 16% PRO, 570 AU WS, 2.2+1.1 Msol, it is possibly binary and needs an orbit.

14h 19m 25.83s -18° 31' 25.0" P.A. 355.00 sep 3.6 mag 7.35,10.68 Sp A3m+A8/F2 dist. 127.06 pc (414.47 l.y.)

STF1523 AB: 178; 200x: Alula Australis. Light yellow unequal stars, well split.  No Gaia parallax data.  SOC grade 1 orbit, 59.89-year period, currently apastron to the south east, it will be due east in 2045.

11h 18m 10.90s +31° 31' 45.0" P.A. 152.00 sep 2.3 mag 4.33,4.80 Sp F9V+G9V dist. 10.42 pc (33.99 l.y.)

STF1852 AB: 178; 140x: 3Dm, very wide. 48% PRO, 1,567 AU WS, 1.5+0.6 Msol, but RVD 3.2 > EV 1.6, it is not binary.

14h 30m 00.14s -04° 14' 49.9" P.A. 267.00 sep 24.9 mag 7.09,10.60 Sp F2V dist. 56.92 pc (185.67 l.y.)

STF1870 AB: 178; 140x: White, 2 Dm, well split. -5% PRO, it is not likely binary.

14h 42m 55.10s +08° 04' 34.3" P.A. 229.00 sep 4.8 mag 7.46,9.98 Sp F2 dist. 198.02 pc (645.94 l.y.)

STT 209 AB: 178; 140x: 3 Dm, well split.  64% PRO, 1,012 AU WS, 2.8+1.2 Msol, but RVD 3.7 > EV 2.6, it is not binary.

09h 53m 17.23s +50° 37' 16.3" P.A. 309.00 sep 4.9 mag 7.41,10.31 Sp G8IV dist. 196.85 pc (642.12 l.y.)

STT 258 AB: 178; 140x: Wide 3 Dm.  1% PRO with 0.8% error, 1,899 AU WS, 2.7+1.1 Msol, but RVD 4.2 > EV 1.9, it is not binary.

12h 54m 13.34s +82° 31' 03.8" P.A. 71.00 sep 10.5 mag 7.25,10.59 Sp K0 dist. 166.94 pc (544.56 l.y.)

STT 281 AB: 178; 280x: Very fine light orange stars, very closely split, 2 Dm, B is a fine point of light.  No Gaia parallax data for B, but an orbit should be tried.

14h 20m 20.85s +08° 34' 56.3" P.A. 166.00 sep 1.5 mag 7.71,9.69 Sp G5

STT 305 AB: 178; 140x: Bright pair, 2 Dm, well split, yellow-white stars.  90% PRO, 1,123 AU WS, 3.5+1.2 Msol, but RVD 4.6 > EV 2.7, it is not binary.

16h 11m 39.60s +33° 20' 33.8" P.A. 263.00 sep 5.7 mag 6.44,10.17 Sp K2III dist. 154.56 pc (504.17 l.y.)

STT 522 AB: 178; 140x: Faint and wide B with averted vision only.  40% PRO, 3,604 AU WS, 3.0+0.9 Msol, with a strong PMV, it is likely binary and needs an orbit

09h 53m 54.04s +64° 47' 20.2" P.A. 124.00 sep 14.5 mag 7.50,12.10 Sp K0 dist. 219.78 pc (716.92 l.y.)

Titan shadow transit of Saturn

It's been a frustrating observing season, with hazy skies, poor seeing, and marine layers rolling in every night.  The night of 6/15-16 was to feature a rare shadow transit of Titan across Saturn.  This happens every 18 years or so, and there will be several more transits in the coming months, but since we're heading into fire season, I wanted to be sure to see this one.  For this transit the shadow would move close to the middle of Saturn, while the others would be more toward the polar region and be somewhat more difficult to see.

I drove up to Henry Coe in the late evening, intending to get above the Bay's marine haze and to have a good view to the east.  I emailed the rangers a couple days in advance, but the gate was locked when I arrived, and there weren't any rangers at the visitor's center.  I parked outside the gate and carried all my gear to the other end of the lot, with a view of the eastern horizon.

I used my C8 on the G11 mount.  The mount is overkill but was actually a good decision since it remained windy all night.  Transparency was on the poor side and seeing was atrocious.  I had some pointing problems with the mount (I'm not used to it yet), so I didn't bother with any purposeful observing.  I brought my night vision device and am very pleased I can reach focus with it in prime configuration in the C8, achieving a nicely illuminated image at a "normal" image scale of around a half degree.  I made a round of various Messier & NGC globular clusters in Sagittarius -- all of which I've seen before, so I didn't take notes.  All the globular were resolved to their cores, bright, and the star fields were very rich.  The views are at least as good as my 20-inch would be visually in a dark site.  I'm very happy to have the versatility of using the device for more than just large nebula.

But I did view some large nebula all the same.  I scanned around using Ha and the 3x objective looking many things I've seen before.  The sky was washed out and the nebula were not as bright or detailed as they would be from a darker site.  All the same, I noticed to the far southern horizon Gum 53, below Sivan 8.  It was very large, fairly bright (even considering it was in Gilroy's light dome), and dual fan shaped -- two wings with a dark V-shape in between.  Astro photos show many dark nebula trunks coursing through it, but I didn't see such detail since I was using low magnification, but I did see very faint streams of nebula running between it up to Sivan 8. 

Around midnight I tried to sleep in my car, intending to wake up at 3:00am when Saturn should be well risen and the shadow transit should be approaching its midpoint.  But I didn't sleep very well and got up at 2:30am.  I looked at the 3rd quarter moon for a while.  Seeing was still soft, transparency a little worse, and it was still gusting.  Saturn looked very poor when I first slewed to it, I could barely make out any bands and only saw a small formless dark smudge where the shadow should be.  I touched-up my collimation and continued to observe.  After 20 minutes or so, at 3:30am, the seeing settled down enough to give me a fine view of the small dark dot of shadow, just below the very thin rings (which appeared as a dark slash through the planet -- viewed nearly edge on they weren't reflecting so much light back).  In moments of best seeing, I could see the very small, tiny points of Dione & Tethys, and even Enceladus which was a brightening on the outer edge of the rings.  Rhea was easy and bright further west from the system.

  

Mission accomplished, I started packing at 4:00am and drove home.  There are more events in the weeks to come and hopefully I can see them (maybe even from home).