Add the field plan for the 12 August 2026 total eclipse from Menorca

Menorca sits inside the path of totality, but the geometry is extreme
and it drives every decision in the plan: the Sun is 2 degrees above
the horizon at maximum, on azimuth 288, and totality lasts 1 minute
12 seconds at Ciutadella before the Sun sets at 20:42.

Two consequences follow from that 2 degrees. The light travels through
roughly twenty times more atmosphere than at the zenith, so everything
is dimmer, softer and redder than any published exposure table assumes
and the histogram has to be the authority rather than a chart. And a low
hill, a building or a haze bank on the sea horizon hides the entire
event, so an unobstructed west-north-west view matters more than
anything else about the site.

That produces a genuine trade-off worth recording. Totality runs 1m38s
at Mahon against 1m12s at Ciutadella, because the centre line favours
the south-east - but Mahon is on the east coast, so from there the view
towards 288 degrees crosses the island with Monte Toro in roughly that
direction. Horizon beats duration: 26 extra seconds is a bonus, a
blocked horizon is total loss. The plan therefore recommends a west or
south-west coastal site.

The plan also corrects an idea that was on the table: a photographic ND
filter is not a solar filter. Standard NDs cut visible light while
passing infrared largely unattenuated, which is where the heat is, and
that will damage a sensor. The requirement is a certified ISO 12312-2
filter around OD 5 on the front of the lens, with the specific warning
that Baader's AstroSolar Photo Film ND 3.8 is camera-only and unsafe to
look through, while the ND 5.0 safety film does both jobs.

The Star Adventurer GTi is explicitly excluded from eclipse day.
Seventy-two seconds needs no tracking, and polar aligning in bright
twilight towards a 2 degree Sun is impractical. It earns its place on
the night skies of the same trip, not on the 12th.

Kept in this repo rather than in a notes app because it is worked out
from real numbers, it will be revised as the date approaches, and the
reasoning behind each decision is the part worth keeping.

README.md

@@ -22,6 +22,12 @@ pipeline should be able to reproduce those results exactly.
 `session-scripts/restructure.py` - reorganises a flat session directory into the
 named layout below. Idempotent, dry run by default.
 
+`observing/` - plans for observing sessions that are not remote-telescope runs.
+Currently the total solar eclipse of 12 August 2026, seen from Menorca. These
+live here rather than in a notes app because they are worked out from real
+numbers, they get revised as the date approaches, and the reasoning behind each
+decision is worth keeping.
+
 ## Pointing the scripts at a session
 
 ```

observing/eclipse-2026-menorca/PLAN.md

@@ -0,0 +1,253 @@
+# Total solar eclipse - Menorca - Wednesday 12 August 2026
+
+Field plan for a Sony A7 on a tripod. Times are local (CEST, UTC+2).
+
+---
+
+## The timings
+
+Figures below are for **Ciutadella** (west coast). Totality length varies across
+the island - see "Where to stand".
+
+| Event | Time | Sun altitude |
+|---|---|---|
+| **C1** partial begins | 19:37:10 | 12° |
+| **C2 totality begins** | **20:30:09** | ~2° |
+| Maximum | 20:30:45 | **2°, azimuth 288° (WNW)** |
+| **C3 totality ends** | **20:31:21** | ~2° |
+| C4 partial ends / sunset | 20:42:00 | 0° |
+
+**Totality: 1 minute 12 seconds.** Eclipse magnitude 103.1%.
+
+Two numbers govern this whole plan:
+
+- **2° altitude.** You are looking through roughly 20 times more atmosphere
+  than at the zenith. Everything is dimmer, softer and redder than any standard
+  eclipse guide assumes.
+- **72 seconds.** No second attempt, no time to solve problems.
+
+---
+
+## Where to stand
+
+**Horizon beats duration.** At 2° altitude a low hill, a building or a haze
+bank on the sea horizon hides the entire event. The requirement is an
+unobstructed view toward **azimuth 288°, west-northwest**.
+
+Duration varies across the island: **Mahón 1m38s**, **Ciutadella 1m12s** - the
+centre line favours the south-east. But Mahón is on the *east* coast, so from
+there you would be looking WNW across the island, with Monte Toro (358 m) in
+roughly that direction. A clear sea horizon is worth more than 26 extra
+seconds.
+
+Best compromise: a **west or south-west coastal site**, which gives open sea at
+288° while sitting further south for a slightly longer totality.
+
+- **Cap d'Artrutx / Far d'Artrutx** (south-west corner) - open sea to the WNW,
+  long low cliff promenade. The usual recommendation, so expect crowds.
+- **Punta Nati** (north-west) - rugged, open, few obstructions.
+- **Ciutadella** clifftop promenade and harbour - accessible, urban.
+
+Named sites will be busy and vehicle access may be restricted, as it already is
+at official sites on Mallorca. Any quiet west-facing cliff works equally well:
+the requirement is horizon, not postcode.
+
+**The real weather risk is a cloud bank sitting on the western horizon** -
+invisible from inland, fatal at 2°. A sea horizon gives the best odds.
+
+---
+
+## What to take
+
+### Buy now - this is the long pole
+
+**A certified solar filter for the front of the lens.** Not an ND filter: a
+photographic ND passes infrared largely unattenuated and will cook the sensor.
+You need ISO 12312-2 / around OD 5.
+
+- **Baader AstroSolar Safety Film ND 5.0** - cheap, excellent, cut to size and
+  mount in a card cell. **Careful:** Baader also sell *AstroSolar Photo Film
+  ND 3.8*, which is for cameras only and is **not safe to look through**. For a
+  single filter that does both jobs, take the **ND 5.0**.
+- Or a ready-made screw-on/slip-on solar filter sized to your lens.
+- **Eclipse glasses (ISO 12312-2) for everyone in the party.**
+
+Order in the next few days. There are three weeks left and this is the one item
+with no substitute.
+
+### Camera kit
+
+- Sony A7 + **wide-to-standard lens (24-70 mm)** - this is the primary lens
+- **200-300 mm** if you have it, for a tighter corona frame
+- **Not 500-600 mm.** At 2° the seeing will destroy fine detail and you will
+  fill the frame with shimmer
+- **Sturdy tripod.** Coastal cliff, evening breeze, low sun - stability matters
+  more than weight saving
+- A head that repoints quickly and low: at 2° you are shooting almost level
+- **2-3 spare batteries**, fully charged
+- **Fast, formatted SD cards** with plenty of space
+- **Remote release or intervalometer** so you never touch the camera
+- **Gaffer tape** - to secure the filter against wind and lock focus
+
+### Leave at home
+
+The **Star Adventurer GTi**. Seventy-two seconds needs no tracking, and polar
+aligning in bright twilight toward a 2° Sun is impractical. Bring it on the trip
+for the night skies - Menorca is dark and August is good for the Milky Way -
+but it plays no part in eclipse day.
+
+### Everything else
+
+Red torch, water, warm layer (the temperature drops noticeably at totality),
+insect repellent, a folding chair, and a phone with this plan and a countdown
+timer. Optionally a second camera or phone on its own tripod recording wide
+video unattended.
+
+---
+
+## Before you go
+
+1. **Fit and check the filter.** Mount it, then hold it up to a bright lamp and
+   look for pinholes. Any hole means it is scrap.
+2. **Practise on a sunset at home.** This is the single most valuable thing you
+   can do. Shoot the Sun through the filter when it is 2-5° above the horizon
+   and write down the settings that work. That calibrates for the real
+   atmospheric extinction, which no exposure table accounts for.
+3. **Practise the filter-off transition** until you can do it in a few seconds
+   without looking, without knocking the tripod.
+4. **Set the camera up once, properly:**
+   - RAW (not JPEG)
+   - Manual exposure, manual ISO - no auto anything
+   - Manual focus
+   - White balance: Daylight, not auto
+   - Long-exposure noise reduction: OFF (it doubles every exposure time)
+   - Steady-shot / IBIS: OFF on a tripod
+   - Drive mode: continuous or bracketing, with the remote release
+5. **On arrival, scout the site** and check the horizon at azimuth 288° with a
+   compass app. Do this on a previous evening if you can - the Sun sets in
+   almost the same place each night this time of year.
+
+---
+
+## Eclipse day, step by step
+
+### Afternoon
+Check the forecast, specifically for **cloud on the western horizon**. Decide
+the site. Travel early - roads will be busy and parking will fill.
+
+### T-3 hours (about 17:30)
+Arrive. Set up the tripod. Frame roughly where the Sun will be at 20:30 -
+azimuth 288°, just above the sea.
+
+### T-90 minutes (19:00)
+- Fit the filter and tape it on.
+- **Focus manually**: magnified live view on the Sun's edge, focus for the
+  sharpest limb, then **tape the focus ring**. Autofocus will hunt and fail.
+- Take test frames. Check the histogram, not the screen brightness.
+- **Decision point:** if the western horizon is clouding over, this is when to
+  move. The island is small; later than this and you are committed.
+
+### 19:37 - C1, first contact
+The Moon takes its first bite. Start the partial sequence: **one frame every 5
+minutes**. That gives about 10 frames for a composite sequence.
+
+### 19:37 to 20:25 - the partial phases
+The Sun drops from 12° to 2°, and **dims continuously and steeply** as it sinks
+into thicker air. No single exposure works for the whole hour.
+
+- Start around **f/8, ISO 100**, shutter near 1/500 (confirm from your practice
+  session).
+- **Re-check the histogram every 5 minutes** and lengthen the exposure as the
+  Sun drops. Expect to end several stops slower than you started.
+- Keep ISO low while you can; raise it later rather than let the shutter get so
+  slow that shimmer smears the disc.
+
+### 20:25 - stop fiddling
+- Final framing. If using the wide lens, compose for **corona over sea**, with
+  the horizon low in the frame.
+- Set the totality bracket ready to fire (see below).
+- Take the lens cap off, keep the solar filter on.
+
+### 20:29 - watch
+Light goes strange, colour drains, the temperature drops. Look west for the
+approaching shadow over the sea.
+
+### 20:30:09 - C2. FILTER OFF
+The diamond ring. **Remove the solar filter** - the whole point of totality is
+that it is safe and the filter makes it invisible.
+
+- Fire the bracket immediately.
+- **Then stop and look at it.**
+
+### 72 seconds of totality
+One bracket sequence is enough. You are 25% of the way through totality by the
+time it finishes. Spend the rest with your eyes, not the viewfinder - a
+2°-altitude totality over the Mediterranean is a rare sight and it will be over
+before it registers.
+
+### 20:31:21 - C3. FILTER BACK ON
+At the first bead of returning sunlight, filter back on and eclipse glasses
+back on. The Sun is now setting into the sea; the remaining partial phases will
+be lost in the horizon haze within a few minutes.
+
+### 20:42 - C4 / sunset
+Done. Pack slowly, let the traffic clear, and look at the twilight.
+
+---
+
+## Exposure settings
+
+Treat these as **starting points to refine at your practice sunset**. Extinction
+at 2° is severe and variable with haze, so the histogram is the authority, not
+this table.
+
+### Partial phases (filter ON)
+| Sun altitude | Aperture | ISO | Shutter (start point) |
+|---|---|---|---|
+| 12° (C1) | f/8 | 100 | ~1/500 |
+| 8° | f/8 | 100 | ~1/250 |
+| 5° | f/8 | 200 | ~1/125 |
+| 2-3° | f/8 | 400 | ~1/60 or slower |
+
+### Totality (filter OFF)
+The corona spans an enormous brightness range, so **bracket wide**: no single
+exposure captures both the inner corona and the outer streamers.
+
+- **f/5.6-f/8, ISO 400-800**
+- **Bracket 1/500 → 2 s**, 7-9 frames, one stop apart
+- Add roughly 3 stops over standard eclipse tables to allow for the extinction
+  at 2°
+- The **diamond ring** wants the fast end: 1/500 to 1/1000
+- **Wide-field shot**: 24-35 mm, ISO 800, 1/30 to 1/8 - captures corona, sea and
+  the 360° twilight glow. This is the picture most likely to be a keeper.
+
+---
+
+## Safety, in one place
+
+- **The filter stays on at all times except between C2 and C3** (20:30:09 to
+  20:31:21).
+- **Never use a photographic ND filter** for the partial phases.
+- **Tape the filter on.** A gust removing it mid-exposure damages the camera.
+- **Check the film for pinholes** before each session.
+- **Eclipse glasses for eyes** during all partial phases.
+- **Naked eye is safe only during totality.** At the first returning bead,
+  glasses back on immediately.
+
+---
+
+## If it goes wrong
+
+- **Cloud on the horizon:** decide by 19:00 and move. Menorca is about 50 km
+  end to end, but roads will be busy - do not leave it late.
+- **Missed the bracket:** the wide-field shot is the keeper. Prioritise it.
+- **Camera problem during totality:** stop, and watch. You cannot fix a camera
+  in 72 seconds, and the memory is worth more than the file.
+
+---
+
+## The one rule
+
+**Look at it.** Seventy-two seconds is very short, the corona at 2° over the sea
+will be extraordinary, and no photograph you take will be the reason you
+remember it.