Return to: Big Bear Solar Observatory (BBSO)
Big Bear Lake, California
Latitude: 34 15.505' N, Longitude: 116 55.278' W, Altitude: 2060 m

Glenn Schneider (Steward Observatory, The University of Arizona)
in collaboration with Jay Pasachoff (Williams College)

With sincere thanks for the help and accommodation by the staff at BBSO.

("People pictures" [non-transit photos on this page] courtesy of Evan Zucker and Paula Eisenhart) 

"Uninspiring" might aptly describe the blank canvas of the face of the Sun when fully devoid of any sunspots typifying its featureless appearance during the now-occurring doldrums of sunspot minimum in its 11 year cycle of solar activity.  While such vast emptiness held on the morning of 11 November 2019, the uniformity of that nothingness was broken by a tiny dot too small to be perceived with the human (filter-protected) eye, but with even modest optical aid was seen in isolated silhouette against the background of the solar photosphere (see below).  The "dot" being the diminutive planet Mercury, caught in the act at local sunrise near mid-solar transit from Big Bear Lake, California (and many other places blessed with clear skies on the Sun-facing side of the Earth).

On an otherwise empty solar canvas, a first small-telescopic glimpse of diminutive MERCURY IN TRANSIT (look carefully!).
 Low to the horizon and still at large air-mass at 144951 UTC.
(Photo: Questar 3-1/2", f/16, (EFL 1422mm), ISO 500, 1/500 s, Questar optical density 4.8 full aperture solar filter, Nikon D800)

Such Mercurian transits aren't particularly rare, occurring on average 13 to 14 times per century, but when they do occur they are fascinating events to observe giving a visceral reality to the workings of celestial mechanics in action.  The last such event occurred only a short 3-1/2 years prior, and was observed then by a small group of us using the facilities of the Big Bear Solar Observatory, home of the 1.6-meter diameter adaptive optics (AO) solar telescope formerly known as simply the "New Solar Telescope", but recently re-christened as the Goode Solar Telescope (GST).  Click HERE for a description of that facility and happenings there during the advent of that most recent prior the Transit of Mercury (ToM) in 2016.

The geometrical circumstances and region of visibility of the 11 November 2019 transit (see Appendix) from Big Bear enabled a return visit for follow-on time-resolved high-resolution AO imaging and visible/near-infrared solar-back-lit spectroscopic observations of the extremely tenuous Mercurian exosphere, and the (partially concurrent*) use of small telescopes and cameras for visible "white light" and Hydrogen-alpha imaging.  With the transit well underway at sunrise, contacts 1 and 2, and most of the first-half of the transit would be out of reach. Our focus, thus, was on the correspondingly latter portions of the transit, and of egress through C3 and C4.  *Because of its operational minimum elevation angle restriction of ~ 23 above the horizon, solar acquisition and AO-lock with the GST were limited to approximately the last hour and a quarter of the transit only. 

Near-horizon views to the east (right) permitted mid-transit visual observations on the observatory access road a few degrees above the horizon.  A 3-1/2" white light Questar telescope in the small dome, parallel mounted on a 4" H-alpha telescope spar, acquired the transit at 6 elevation (photo up top).

Observations with the 1.6 m GST AO telescope began at 16:45 UTC with the
Sun above the ~ 23 pointing limit.

TRANSIT 1.6m Goode telescope with Adaptive Optics Wavefront Correction

Speckle-Reconstructed AO Imaging with the GST

(Click HERE to view/download the Movie!)

<-- To the left is the 1st reduced frame of Mercury-in-transit seen in high-resolution against the solar photospheric granulation with the GST wavefront control system in AO lock.  Reduced frames then proceed with an ~ 6 s cadence until shortly after C4. 

Imaging was done with a 10 wide TiO filter centered at 7058 in the BBI (Broad Band Imager) instrument with a PCO-2000 high speed CCD camera.

Details from John Varshik:

- The PCO camera takes bursts of 100 frames in an interval of ~ 6 s from which the 70 best frames are saved and from which a single speckle-reconstructed frame is produced.

- The speckle-reconstruction algorithm assumes the only thing changing in each 100 frame burst is the Earth's atmosphere, which clearly is not the case (given the relative motion of the background photospheric granulation w.r.t. Mercury).

(N.B.: The thin concentric light and dark rings around the periphery of Mercury's disk are artifacts from the speckle-reconstruction algorithm.)

--> Thanks to John Varshik, Claude Plymate, and the BBSO staff

C3/Black Drop Goode 1.6m telescope with Adaptive Optics Wavefront Correction

A minimal, but detectable, Black Drop signature is seen circum-Mercurian image isophotes from the raw GST BBI 18:02:55 UTC frame (3 seconds prior to geometrical C3/internal tangency predicted for 18:02:58 UTC); see below.  This display frame is stretched linearly over an 8-bit imaging min-to-max dynamic range from 25 to 158 DN.  The image is displayed with a contouring color table that switches from orange-to-blue mid-scale.  The color table is modulated from min to max with 6.25% intensity contours peak-to-peak. The small (purple) isophotal extrusion along the point of internal tangency connecting the slightly tear-dropped disk of Mercury and the inwardly "dimpled" photospheric limb at that point is evidence for a Black Drop effect.  Compare, for example, to Figure 6E of Schneider, Pasachoff, and Golub, 2004 (Icarus, 168, 249).

EGRESS - 0.089 meter (Questar 3-1/2") telescope with natural seeing

Full disk solar image at 18:02:22 (geometrical C3 - 36 seconds); Mercury at upper right.
(Photo: Questar 3-1/2", f/16, (EFL 1422mm), ISO 500, 1/1600 s, Questar optical density 4.8 full aperture solar filter, Nikon D800)

180240 180259 180309 180325
180340 180356 180411 180428 180440
Egress sequence: Top-left to bottom right with corresponding UTC.
First frame same data as full disk image above.
Third frame at 180259 UTC is 1 s after predicted geometrical C3 with no evidence of Black Drop above the noise.
(Photos: Questar 3-1/2", f/16, (EFL 1422mm), ISO 500, 1/1600 s, Questar optical density 4.8  full aperture solar filter, Nikon D800)

First frame from an extended egress Time-Lapse "Movie" from 172114 (shown above) to 180440 UTC
Click HERE to view/download the Movie!
Frames 172114 to 175743 UTC cadence ~ 5m per frame, 175743 to 180440 UTC cadence ~ 15s per frame
"Playback" rate: 1 fps.

The "Crew" and Memories of the Transit
(click on any picture to "enbigenate")

Evan Zucker, Glenn Schneider, Claude Plymate, Jay Pasachoff, Muzhou Lu
Glenn Schneider, Jay Pasachoff in the small dome

Glenn in his almost-"Where's Waldo" hat Glenn and Jay "transit break"/wool hat contest

Evan and Glenn focus check
Absurdly heavy-duty (but sturdy!) mount for a Questar 3.5"

John Varshik and Claude Plymate in the GST control room
Coming up on Contact 3

Duct Tape Never Leave Home Without It!

Appendix Topocentric Circumstances of the Transit from BBSO

BBSO Coordinates:  34.2584 N, 116.9213 W (34 15' 30", 116 55' 17")
BBSO Altitude AMSL: 2,060m (6,760 ft)

Angular Diameter of Sun:    1938.592" (@sunrise); 1938.712" (@ C4)
Angular Diameter of Mercury:   9.955" (@sunrise);    9.949" (@ C4)

Topocentric Transit Event Circumstances

EVENT*  PST      UTC       ALT.  AZI.       
SUNRISE 06:18:18 14:18:18  -0.5 110.8  P      Z  
MAX**   07:20:26 15:20:26  11.0 120.1   24.2 288
C3      10:02:58 18:02:58  34.1 154.2  298.6  39
C4      10:04:39 18:04:39  34.3 154.7  298.6  39

*  Contacts 1 and 2 not visible (occur before sunrise)
** Impact Distance at MAX = 74.7"

 Topocentric Track from BBSO: Sunrise to C3

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