Observation planning

The Planner workspace manages observing lists, predicts how well each object will be seen with your equipment tonight, plots altitudes through the night, and keeps a logbook of what you observed. Together with the Sky chart it covers everything you need to plan an observing session.

Contents

• Layout
• Observing lists
• Adding objects
• The plan table
• Generating a list for tonight
• The altitude graph
• The logbook
• Importing and exporting
• How visibility is predicted
• Tips for a good plan

Layout

Area	Contents
Observing lists (left)	Your lists and the buttons to manage them
Centre, top	Toolbar, the plan table for the selected list
Centre, bottom	Nightly planner — altitude graph
Logbook (right)	Observations of the selected object

Observing lists

A list is a named set of objects with your notes and an "observed" tick for each. Sidralune starts with a Messier catalogue list and an empty Tonight list. Lists are saved automatically in %LOCALAPPDATA%\Sidralune\Settings\planner.json.

Button	Action
New	Create an empty list
Rename	Rename the selected list
Delete	Delete the selected list (asks for confirmation)
Import	Import objects from a CSV or text file
Export	Export the list as CSV

The number after each list name is how many objects it contains.

Adding objects

• Type a name in the box on the toolbar and click Add (or press Enter). Stars, deep-sky objects and planets (Mars) are accepted.
• In the Sky chart, select an object (including comets and asteroids) and click Add to list, or right-click it and choose Add … to observing list.
• In Databases → Local catalogues, select rows and click Add to plan.
• Use Generate best for tonight… to build a list automatically.

Remove deletes the selected rows from the list.

The plan table

For every object in the active list, Sidralune computes tonight's circumstances for your site and equipment:

Column	Meaning
✓	Tick when you have observed the object
Object, Type, Con, Mag, Size	Catalogue data
Rise, Transit, Set	Local times; "circ." for circumpolar objects
Best	When the object is best seen during the dark hours, taking altitude, moonlight and twilight into account
Alt now	Current altitude
Visibility	Predicted detectability at the best time: Obvious, Easy, Detectable, Difficult or NotVisible
Best ×	The magnification that gives the best view with the active telescope
Moon	Angular distance from the Moon
Notes	Your notes. Click the cell to edit

Click a column heading to sort, for example by Best to get an observing order through the night. Tick Up tonight only to hide objects that do not rise above the horizon during the dark hours. Recalculate refreshes the table, for example after changing the time.

The table recalculates automatically when you change the active site. After changing the time or your equipment, click Recalculate.

Generating a list for tonight

Generate best for tonight… (or the Planner: generate tonight's best list command) asks which kind of object you want:

• All deep-sky
• Galaxies
• Nebulae (emission, reflection, supernova remnants and cluster-nebula complexes)
• Clusters (open and globular)
• Planetary nebulae

Sidralune then examines every deep-sky object brighter than magnitude 13 at hourly steps through tonight's dark period. An object counts only while it is above 25° altitude. At each step it predicts the detection margin with your telescope, eyepiece, eyes and sky, including moonlight. The 60 objects with the largest margins become a new list named after the type and date, for example "Galaxies 2026-10-18". While it works, the button waits and Stop, next to it, ends it; a stopped run adds no list.

The altitude graph

The Nightly planner — altitude graph plots, for the selected objects (up to eight), their altitude from evening to morning. It also shows:

• the Moon's altitude,
• shaded bands for twilight and darkness,
• a horizontal line at 30°, a common minimum for good views,
• a marker at the current time.

Select several rows in the table to compare objects and decide the order of the night.

Times on the axis are the site's local clock. On the night the clocks change, time still runs evenly along the axis: when summer time ends, the repeated hour is labelled twice (for example 02:00 appears two times), and when it begins, the skipped hour is missing from the labels. The Sky chart's altitude graph works the same way.

The logbook

Select an object to see its earlier observations in the Logbook on the right: date, a rating in stars, the instrument and your notes.

Click Log observation… to record a new one. The form is pre-filled with the time, site, telescope and eyepiece, and has fields for:

Field	Meaning
Seeing	Atmospheric steadiness on a 1–5 scale
Transparency	How clear the sky was, 1–5
SQM	Measured sky brightness, if you have a meter
Rating	1 to 5 stars
Notes	What you saw

Export in the logbook card writes all observations to CSV with the columns UTC, Object, Site, Instrument, Eyepiece, Seeing, Transparency, SQM, Rating and Notes.

Importing and exporting

Import reads a CSV or text file with one object per line. The first column is the object name; a header row named Name or Object is skipped. Each name is looked up in the catalogues, so M 31, NGC 891 or Albireo all work. Other columns are ignored.

Export writes Name, Type, Constellation, RA, Dec, Mag, Size_arcmin, Observed and Notes. The file opens in any spreadsheet program, and can be imported again or shared with other observers.

How visibility is predicted

Sidralune predicts whether you will actually see an object, not just whether it is above the horizon. The model, used in the Planner, the Tonight page and the Sky chart, works in four steps:

1. Sky brightness at the object's position. It starts from your site's SQM value, brightens towards the horizon, and adds moonlight with the Krisciunas & Schaefer (1991) model (which depends on the Moon's phase, altitude and distance from the object) and twilight from the Sun's altitude.
2. The object's light at your eye. Its magnitude is dimmed by atmospheric extinction (your site's k(V) times the airmass) and by the telescope's transmission and central obstruction, and gathered by its aperture.
3. Contrast at each magnification. Magnification darkens the background once the exit pupil is smaller than your eye's pupil, and spreads extended objects over a larger area. Small objects are blurred by seeing and diffraction. Sidralune scans the useful range of magnifications.
4. The detection threshold. Schaefer's (1990) model of night-vision thresholds, with spatial summation for extended objects (Ricco's law), gives the faintest detectable object on that background. Your age sets the eye's pupil (about 7.8 mm at 20, 0.45 mm less per decade) and your experience and averted vision lower the threshold.

The result is a margin in magnitudes: how much brighter than the threshold the object is at the best magnification. The rating follows from it:

Margin	Rating
below −0.5	Not visible
−0.5 to 0	Difficult (averted vision)
0 to 0.7	Detectable
0.7 to 1.8	Easy
1.8 or more	Obvious

The model is a guide based on laboratory data and typical observers. Your eyes, dark adaptation, transparency and experience on the night all matter. Treat "Difficult" objects as a challenge rather than a promise.

Tips for a good plan

• Set your real SQM, extinction and age in Settings; they make a large difference to the predictions.
• Choose the eyepiece you will actually use as the active one, or check Best × to see which magnification to use.
• Sort by Best to observe objects in the west first, before they set.
• Print a finder chart for each target from the Sky chart before the session.
• Use the Moon column to avoid faint galaxies near a bright Moon.