diff --git a/README.md b/README.md index a8b1cd2..78b1e14 100644 --- a/README.md +++ b/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 ``` diff --git a/observing/eclipse-2026-menorca/PLAN.md b/observing/eclipse-2026-menorca/PLAN.md new file mode 100644 index 0000000..beb8a2a --- /dev/null +++ b/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.