(U. Arizona), Tim Todd (
A total solar eclipse (TSE)
is,
unequivocally, one of nature’s grandest spectacles and most awe-inspiring
events that we can see with our own eyes! But, the elusiveness of
the path of totality for TSE 2021 (Figure 1) has left many
eclipse-chasers
fretting and asking “how the heck am I going to get there?” We now can
answer as we have planned and are vigorously pursuing a unique
opportunity to
view the eclipse
from a high-altitude jetliner in a near-sunrise
moonshadow rendezvous, above the otherwise high-probability occurrence
of clouds below.
Figure
1. TSE 2021 path of totality and EFLIGHT
2021–SUNRISE circumstances tabulation.
Yellow "+" marks the location of our on-centerline Mid-Eclipse
Intercept (MEI) for our ex-Punta Arenas Airbus A321-200
eclipse-flight charter.
By comparison, on the Earth's surface, at the much more distant point
of greatest
duration (
GD) eclipse,
totality is only 9 seconds longer than will be seen from our aircraft.
See
HERE for the
representative extent of circum-Antarctic sea-ice extrusion for early
December.
The
“Sunrise” Mid-Eclipse Intercept
(07:02:14 UTC)
The Moon’s umbral shadow touches down on the
Earth’s surface along our planet’s night/day terminator nearly due
east
of Punta
Arenas. This, serendipitously, is both the closest launch point (along
with Ushuaia) and shortest flight-time for a charter flight to reach
centerline, and in particular the MEI target-point for our “sunrise” EFLIGHT. At
this location, and instant of time, the trajectory of the lunar umbral
shadow stretching back ~ 400,000 km into space will emanate from the
totally-eclipsed Sun on the astronomical horizon (everywhere 90°
from the zenith). Second-by-second, during the 1m 45s of our airborne
totality as
the surface projection of the shadow rapidly decelerates, the lunar
umbra will horizontally sweep around, over, and then engulf the
aircraft in darkness like a broad darkness-inverted searchlight beam.
Those who have seen a similar phenomenon from the ground (e.g., Figure
3)
have
described the effect there as “God’s bowling alley”. This will be even
more accentuated with the 390 km distant terrestrial horizon at 39,000
ft.
depressed by 3.5° from the astronomical horizon (coincident with
the origin of the shadow) as we fly at Mach 0.78 (approx. 447 kts true
air speed) centrally through the
darkness of the Moon’s umbral shadow.
Figure
3. “God’s bowling alley” (TSE 2002 December 04 UTC) as photographed by Carter Roberts at sea level
from Lyndhurst, South Australia.
The eclipsed Sun is 4° above the
at-sea-level-coincident astronomical
and terrestrial horizons.
For
our EFLIGHT
2021–SUNRISE the
totally eclipsed
Sun will be ON the astronomical horizon, but with the apparent
(terrestrial) horizon
depressed by 3.5°.
While the “big show”, of
course, is totality,
the proximity of Punta Arenas to the sunrise line at umbral touchdown
on the Earth provides a unique opportunity to observe TSE 2021 totality
with the rapidly decelerating shadow cone grazing tangentially along
the surface of the Earth (e.g., see Figure 3 with a similar geometry at
mid-eclipse). From our lofty EFLIGHT
venue our SUNRISE aircraft will provide some of the most esthetically
stunning views of the opening terrestrial traverse of the lunar umbra.
Our “Totality Run” (TR) approach to the MEI (where at MEI itself the center of
the
lunar
umbra first and fully obliquely touches down on the Earth at 39,000 ft
AMSL) begins 25.2 minutes
prior to mid-total eclipse. At that “TR Start” time (06:37:02 UTC) the
lower limb of the
Sun in partial eclipse will touch and then rise over the -3.5°
depressed terrestrial horizon (see Figure 4). The increasingly
partially-eclipsed Sun
then ascends toward totality with a diminishing solar photospheric
crescent fully obscured by the Moon at the end of the C2 diamond ring
at 07:01:23, heralding the start of 1m 45s of totality.
Figure 4. Schematic depiction of Sun
rising during partial eclipse
ingress from 39,000 ft. as seen from EFLIGHT
2021–SUNRISE with the Sun’s lower limb
on the terrestrial horizon at
the start
of the Totality Run.
Though only the “opening act” preceding
totality, this proximal MEI location to Punta Arenas and within the MPN
ETOPS60 circle permits us to
program an approach for the SUNRISE totality run track that will
initially present a 47% partially eclipsed Sun at lower-limb sunrise. The partially-eclipsed sunrise also marking the start of
our “totality run”, like totality itself, will be visible from the left
side of the aircraft*. (*Due to the low elevation angle of the
eclipse, from a few seat
rows flanking the third
emergency exit door the
aircraft wing itself will block this view, and the view of totality as
well. Thus,
these few specific rows will not be
used for eclipse viewing.)
At this extreme line-of-sight sunrise viewing
geometry, as the Sun ascends the apparent horizon, its
partially-lunar-occluded disk may take on an oblate or even more
extreme
morphologically distorted shape due to differential atmospheric
refraction with the possibility of a partially-eclipsed
omega effect, or
even more
extreme distortions
and/or a green flash
while rising in partial-eclipse.
At our
07:02:14 MEI, thanks to the aircraft’s
39,000 ft
altitude, the totally eclipsed Sun
will gloriously stand 3.5°,
i.e., 14 solar radii, above the
depressed terrestrial horizon and “straight out” the left-side passenger
windows. There, the umbral
axis will lie in the horizontal plane parallel to surface of the Earth with
the
Moon’s conical shadow stretched out and over the astronomical
horizon
as
seen in perspective sweeping over a distance of nearly 400 km, framing
the Sun’s glorious corona as
it circumscribes and enshrouds
the ashen lunar disk for a glorious 1m
45s of totality.
This
will be a TSE viewing flight
of an entirely different flavor!
CENTERLINE and
Mid-Eclipse-Intercept
(MEI)
The total phase of TSE 2021 is optimally
viewed from along the “centerline” of the PoT
midway between the northern and southern path limits. The very center
of the Moon’s shadow, which traces out the centerline of the PoT, is
where (for any location along the path) the totality duration is
longest, the sky is darkest (amazingly so at 39,000 ft*), and the view
of
totality is optimal. (*Our
high-level
eclipse-viewing altitude of 39,000 ft. AMSL that is above ~ 80%
of the
Earth’s atmosphere will put us into the tropopause, where the
concerns of
sub-polar weather (and clouds) will remain in the troposphere below.) Our EFLIGHT is
designed to be precisely on centerline just as the Moon’s shadow
axis reaches that centrally-located position of the aircraft, i.e.,
this is the UTC time-correlated point of “Mid-Eclipse Intercept” (MEI)
around which the rest of the flight is planned.
The centerline of the path of totality, for
all practical purposes, may be expressed as a (UTC) time-correlated set
of waypoints (latitude, longitude) that maps out the central position
of the Moon’s umbral shadow as it traverses the Earth. In principle,
totality may be seen (where accessible and not cloudy on the ground)
anywhere along that path. The TSE 2021 eclipse geometry and local
circumstances guide us in selecting our MEI locations in concert and in
conformance with normal aircraft performance
characteristics and ETOPS60 operational limitations – and (most
importantly!)
above otherwise potentially
problematic sub-polar cloudy weather.
BASELINE
End-to-End Plan
Routing:
The EFLIGHT 2021–SUNRISE
flight plan can be best described as an ~ 5-1/2 hour round-trip flight
to/from the same
originating
location, Punta Arenas, with the inclusion of an additional
critically-defined appx half-hour leg called the “Totality Run” (TR).
It is from there that for 1m 45s, totality centered on 07:02:14 UTC
will be observed with the aircraft at 39,000 ft AMSL
concentrically located along the axis of the Moon’s umbral cone at the
instant of mid-eclipse. The turn onto the totality run is immediately
preceded by a contingency, real-time tunable, “circle and hold” (C&H) segment
for UTC
ground-track synchronization of the start of the TR in the event of a
delayed take-off from Punta Arenas. The end-to-end basically
“triangular” EFLIGHT plans
PUQ→eclipse→PUQ can then be described as:
- take-off (“wheels-up” not push-back)
- airport pattern departure and ascent to
top-of-cruise (TOC)
- outbound cruise to totality run first
waypoint (TRSTART location)
- contingency circle and hold for
up to 45 minutes for UTC synchronization
- release onto totality run at
UTC-correlated TRSTART waypoint (lower-limb sunrise at TRSTART)
- totality run (inclusive of, and
anchored on, the UTC-correlated MEI point)
- inbound return to start-of-descent (SOD)
- descent and pattern approach
- landing
where (1 – 3) and (7 – 9) are as usual on any
flight, but here with (4
– 6) augmenting the usual “point-to-point” plan with the inclusion of
the time-critical Totality Run.
Aircraft:
We have proceeded with our baseline planning for our chartered Airbus
A321-200,
ETOPS60 rated aircraft,
as we are discussing and maturing its flight plan and operational
details
with our aircraft
provider/operator, LATAM Airlines. We predicate our baseline plans for
a true air speed (TAS) of 447 kts (Mach 0.78) for the Totality Run in
particular, also assumed as cruise speed for other pre- and
post-requisite flight segments in
straight-and-level flight.
Flight Duration
(with 45-minute in-air contingency margin):
For baseline plan definition and
tolerance with in-segment flight-time variation for actual
winds-aloft we assume no winds, but provide margins in the end-to-end
plan to compensate for actual
winds aloft in flight. With these baseline
assumptions we estimate the end-to-end duration as closely
proximate to < 5.4
hour. Preliminary ETD 3:24 UTC ex-Punta Arenas (to be
updated/confirmed).
BASELINE Totality Run
Predicated by the MEI UTC and location for EFLIGHT
2021–SUNRISE flight, the end-to-end baseline
totality run may be represented
in simple parametric form with three key time-correlated waypoints
defined by their start, MEI, and end. We
enter the TR run track 25.2 minutes prior to MEI (allowing for
pre-totality sunrise viewing). The TR ends
6 minutes after MEI.
Totality Run Waypoint
|
UTC (hh:mm:ss)
|
Aircraft Longitude
|
Aircraft Latitude
|
TRSTART
|
06:37:02
|
W04806.112
|
S5006.932
|
MEI
|
07:02:14 |
W05110.202
|
S5234.421
|
TREND
|
07:08:14
|
W05157.054
|
S5308.783
|
(all coordinates WGS84 referential datum)
CLICK
HERE for a
multi-parametric tabulation of this
Totality
Run with 1 minute time granularity w.r.t. MEI after
ETOPS60-limited TRSTART (START).
CLICK HERE for an explanation of the multi-parametric tabulation.
TIMING CONTINGENCIES
(pre-planning for success)
The PUQ→eclipse→PUQ
EFLIGHT plan is
designed with more than sufficient time to execute all fight segments. In the unlikely event of a take-off delay, or with
unfavorable outbound winds, our pre-planned, expendable, C&H leg provides an additional in-flight margin of up to 45 minutes for the successful
attainment of the MEI exactly as planned. Beyond this margin, we have
further contingency flexibility to modify the TR if necessary,
maintaining the same MEI by shortening the length of its pre-C2
TR
segment by up to approximately 20 additional minutes.
COMPARATIVE
RISK ASSESSMENT - TSE 2021
Ground-based (including sea-going) TSE observations are inherently “risky” due to the
ever-present possibility of uncooperative weather.
This is the case, in particular, from sky cover obscuration due to
clouds, fog, or
precipitation that differ from eclipse to eclipse and with
location. E.g., for
statistical expectations and discussion specifically germane for TSE
2021 see HERE. Therein
the risk of cloud cover obscuring totality for locations reachable by
ship is summarized by eclipse-weather expert Jay Anderson as “Over the
oceans, cloud cover averages more than 90% {!}”
When path access is
limited (as extremely so for TSE 2021) but not impossible, and nature
conspires against us with high risk of obscuring clouds, some will nonetheless (grudgingly) accept such risks when no other
alternatives are presented.
Such high-risk scenarios, however, are eliminated by employing a high-altitude jet aircraft as a platform for
eclipse observations. Risk is never entirely mitigated, but
typically can be reduced to at most a few percent. E.g., while
the
statistical expectation of opaque cloud above 39,000 ft is vanishingly
small for a sub-polar eclipse such as TSE 2021 where we plan to
intercept, it is non-zero due to other remote possibilities.
E.g.,
one could posit various, but highly unlikely, reasons the
point-of-departure airport could shut down due to low-probability
events, but the percentage
“chance” of that
occurring at requisite take-off time
is counted generously on fingers far less than on one hand.
In the case of our EFLIGHT 2021–SUNRISE scenario, the
risk of not
seeing totality is somewhat “high” by airplane
expectations (but extremely
low compared to anything
else!). That risk is about 4%, and potential flight participants must
understand (and accept) this risk.
This risk comes about from the necessity to plan a requisite
contingency ETOPS60 diversion landing return specifically at the Royal
Air Force (UK)
Mt. Pleasant airport (MPN) in the Falkland (Malvinas) Islands.
MPN is the only existing
facility for such planning that allows us to boot-strap with an ETOPS60
hop to the path of totality (see Figure 1). During the months of
November and
December (climatologically representative of the December 4 eclipse
time of year), approximately 4%* of the time, MPN experiences a
high-wind phenomenon known as “rotor winds” – severe
low-level
turbulence causing a temporary closing of the runway until
subsidence. (*Based on prior year NOTAMS (Notice to
Airmen) statistics; e.g., in
2018
MPN was closed to air traffic for a total of 61 hours out of
1464.) While we do not plan at all to land at MPN, it must be
available (open) to us while we are in the air. Thus, if the MPN runway
closes for this reason (or is forecast/predicted to close) during that
time, we would not be permitted to take off from PUQ. To put in
perspective in comparison to the “next best” option by
ship, the
statistical expectation of the likelihood of success by deploying
into a cloud-free sky with EFLIGHT
2021–SUNRISE is ~ 96%, whereas the “odds" of
successfully viewing the eclipse on the ocean are < 10%
(per
quoted
reference from J. Anderson, above).
WINDOW-SHARING
and ECLIPSE-VIEWING
Probably the most often asked questions related to the
aircraft windows for eclipse viewing are:
- “What are the aircraft windows like?”
- “Could I share a window in
an eclipse-viewing seat row with a partner to watch the eclipse?”
- “Can’t aircraft windows fog or frost up?”
From our many past
experiences we can answer as follows:
1a) QUALITY: Commercial
aircraft windows are not research-grade optics.
Nonetheless, if not optically degraded in some fashion, such windows
are typically more than well suited for visual and/or binocular
viewing of TSEs, and for wide- to intermediate-field photographic
imaging and even low-resolution spectroscopy. Several examples
are offered below. This, of course, depends upon the window quality.
Part of our charter contract requirements to our aircraft
provider/operator specifies the need and protocol to importantly secure the best (and
thus
often typically newest) aircraft in their fleet from the perspective
of defect-free, distortion-free, and scratch/sleek-free windows as a
key factor
in aircraft down-selection. Aircraft with more than a minimal
number of such window artifacts will be rejected from our
consideration. Window cleanliness (free of dust, dirt, oils, or
any other light-scattering materials or particulates), of course, is
also essential; and
well-proven protocols for pre-EFLIGHT
window cleaning (without leaving residual streaks) are called out in a
technical annex to our charter requirements.
Though no
photographs can come close to reproducing the magnificent views
captured on our retinas and interpreted by our visual cortices, here
are a few images taken on prior EFLIGHTs
through their aircraft windows indicative of their suitability for TSE
observing.
Wide-Field
Imaging: View from EFLIGHT
2015 March 20 UTC over the Norwegian Sea at Second
Contact, 35,000 ft.
Canon EOS 5D
Mark III Digital SLR at ISO 1600, 1/60th sec, 14mm EFL f/2.8 Rokinon IF
ED UMC Ultra Wide-Angle Lens used at f/4
Glenn Schneider and Geoff Simms
Coronal
Imaging from EFLIGHT 2015
over the Norwegian Sea, 35,000 ft.
Inner Corona
|
Mid+Outer
Corona
|
|
|
Nikon D3000
+ 300 mm f/5.6 VR lens (ISO 800) – handheld. Left: single frame, right:
5 frame stepped exposure time composite
Glenn Schneider
Click HERE
for some remarkable HDR coronal imaging from EFLIGHT 2003 November
24-23 UTC by
Miloslav Druckmüller and David Finlay – Antarctica, 35,000 ft.
Totality Time-Resolved Coronal
Ramp
Up/Down Imaging from EFLIGHT
2010 July 11 UTC – South Pacific, 39,000 ft.
Nikon DX3
camera at ISO 200 and VR 80-400 mm lens at 400 mm f/5.6. (Double-click
on the image mosaic to view at larger scale.)
Glenn Schneider
Near-Infrared (0.7 to 1.0 micron)
Chromospheric “Flash” Spectrum at C2 from EFLIGHT 2019–MAX (July 2) –
1,100
km N. of Easter Island, 41,000 ft.
1b) METROLOGY. Below is an
annotated photograph that
shows the Airbus A320-family window metrology. This particular
photo was actually taken from our
EFLIGHT 2010 aircraft, which
was an Airbus A319/LR-CRJ. The window
metrology and spacing, however, is identical
to the A321-200 we will use for EFLIGHT
2021–SUNRISE (except where exit row
doors interrupt the otherwise uniform spacing of the windows).
C = 53
cm Inter-window centerline distance
(most windows; a few have larger inter-window spacings)
L = 30
cm Clear-area with trim gasket window-length
W = 21
cm Clear-area with trim gasket window-width
T = 114
cm Top of window to floor vertical distance
B = 86
cm Bottom of window (actual surface, not trim) to
floor vertical distance
D
= 0 cm Top of window protrusion distance
vertical to cabin floor edge [a]
θ = 14
deg Tilt angle (top inward) of window with respect to
vertical [b]
[a] The right
panel figure indicates a downward projection of the window top onto the
floor is inboard (by a distance D) of bottom of the actually slightly
curved wall.
This is typically actually zero, but the
cosmetic wall
floor panel may be different in our charter aircraft [TBD].
[b] The windows themselves, as mounted on the aircraft fuselage, are
tilted inward at the top by appx 14°.
2) WINDOW
SHARING. The low
vertical angle of the Sun (on the horizontal plane, 3.5° above the
terrestrial horizon at 39,000 ft) will greatly facilitate “window
sharing” for those contemplating an observing partner, which can be
much more problematic (and contorting!) for high-solar-elevation-angle
eclipse flights. To aid in visualization, we have a high-fidelity
window template
from Airbus that, if you print to actual size, you can tape to a
wall following the dimensions above and try for yourself. Click HERE
for that template. So the
answer to this second question is – yes. However, what we
do not know yet is the relative positioning of the seats
in individual rows with respect to windows in those rows. So, some
rows will have access to one,
or fractionally more than one, window that will be more easily
shared in some rows than others. We will have detailed
information on this on a row-by-row basis at a later date to inform
flight participants on the best rows suited to their individual needs.
3) WINDOW CONDENSATION/FROSTING:
FULLY
EFFECTIVE MITIGATION. In a nutshell...
1. Click image for close-up of cabin air temperature control
2. Click HERE
to see one of the lamps
most recently used very effectively on EFLIGHT 2019-MAX