Sky chart

The Sky workspace is Sidralune's planetarium and star atlas. It shows stars, deep-sky objects, planets, the Moon, comets and asteroids for your site and time, overlays the fields of view of your equipment, gives detailed information about any object, controls your telescope and prints finder charts.

Contents

• Layout
• Planetarium and Atlas modes
• Moving around
• Finding objects
• Fields of view
• Mirror and invert
• Layers
• Limiting magnitude
• What is drawn and how
• Planets' moons
• Object information panel
• Right-click menu
• Controlling the telescope
• Changing the time
• Printing finder charts
• Exporting images
• Commands

Layout

• The toolbar across the top: mode switch, field-of-view presets, time controls, mirror and invert, layers, print and export, and the find box.
• The chart fills the middle.
• The object panel on the right shows the selected object, its action buttons, detailed information and an altitude graph for tonight.
• A caption at the bottom of the chart shows the local time, site, field of view and limiting magnitude.

Planetarium and Atlas modes

Switch with Planetarium / Atlas on the toolbar.

	Planetarium	Atlas
Orientation	Altitude-azimuth: the horizon is horizontal, as you see the sky	Equatorial: north up, east left, as in printed atlases
Ground and daylight	Drawn (ground below the horizon, blue sky by day)	Not drawn
Typical use	"What is up now and where?"	Star-hopping, framing, printed charts

Both modes use a stereographic projection, which keeps the shapes of constellations and fields of view correct over a wide angle.

Moving around

Action	Mouse	Keyboard
Pan	Drag with the left button	Arrow keys
Zoom	Mouse wheel	+ and −, or Page Up and Page Down
Centre on a point	Double-click
Select an object	Click it
Look north, east, south, west		N, E, S, W (planetarium)
Look at the zenith		Z (planetarium)
Context menu	Right-click

The chart can zoom from the whole sky (200°) down to 36″ (0.01°), close enough to see Charon beside Pluto.

Finding objects

• Type in the find box on the toolbar and press Enter. It accepts names (Albireo, Ring Nebula), designations (M 57, NGC 6720, HIP 95947), planets and their moons (Titan, Oberon), comets and asteroids, and coordinates in the form hh mm ss +dd mm ss.
• Or press Ctrl+K anywhere for the command palette.

The chart centres on the object and selects it. If a name is not found in the local catalogues, try Databases → Online databases → Resolve name, which asks the CDS Sesame service.

Fields of view

The field-of-view list on the toolbar sets the zoom and draws matching indicators:

Preset	Zoom	Indicator
Naked eye (100°)	100°	None
Wide (60°)	60°	None
Binoculars (7°)	12°	6.5° circle for 10×50 binoculars
Finder (5°)	9°	5° circle for an 8×50 finder, plus Telrad rings
Low power (2°)	4°	None
Eyepiece	Fits the eyepiece field	Circle for the active telescope and eyepiece, labelled with the magnification
Camera	Fits the sensor	Rectangle for the active telescope and camera
Custom	Unchanged	None

The eyepiece and camera indicators come from Settings → Equipment. For mosaics and rotated framing, use Astrometry → Framing & mosaics, which shares the same chart.

Mirror and invert

Telescopes show the sky flipped. Match the chart to the view in your eyepiece:

Button	Matches
Mirror	A refractor, SCT or Maksutov with a star diagonal (mirror image)
Invert	A Newtonian reflector or a straight-through finder (rotated 180°)
Both	A Newtonian reflector with a diagonal or similar setups

The settings are also used when printing.

Layers

Layers opens a menu of everything the chart can draw. Tick or untick each item:

Group	Layers
Objects	Stars, Star names, Bayer / Flamsteed, Deep-sky objects, Deep-sky labels, Planets, Sun and Moon, Comets and asteroids
Constellations	Constellation lines, Constellation names, Constellation boundaries, Milky Way
Reference lines	Equatorial grid, Alt-azimuth grid, Ecliptic, Galactic equator, Meridian
Surroundings	Horizon and ground, Atmosphere (daylight sky), Cardinal points
Equipment	Telescope position, Field-of-view indicators, Telrad rings
Calculation	Refraction

The Limiting magnitude submenu sets the faintest stars shown (4.0 to 12.0) and whether the chart goes deeper as you zoom in. The current choices are ticked.

Limiting magnitude

The value chosen in Layers → Limiting magnitude (6.5 by default) is the faintest star magnitude shown for the whole sky. With Deeper when zoomed in ticked (the default), the limit grows by about 2.2 magnitudes for every tenfold zoom, so the chart always has a useful number of stars without clutter. Below a 1° field it grows faster, so at the narrowest field (36″) every star in the installed catalogue is shown, whatever limit you chose. Untick it to keep exactly the chosen limit at every zoom. The limit in use is shown in the caption at the bottom of the chart.

Deep-sky objects have their own limit, and their labels appear progressively as you zoom in. With the PGC galaxies installed (Settings → Data), galaxies that are not NGC/IC objects appear once the field is 15° or narrower. With the PGC galaxy magnitudes installed too, those within the deep-sky magnitude limit are shown, brightest first; galaxies at least a third of the field width in arcminutes across (5′ at 15°) are shown as well, which covers those without a magnitude. They are labelled with their PGC number below 3°. Comets and asteroids are shown down to about two magnitudes fainter than the star limit (at most magnitude 15).

What is drawn and how

• Stars are dots sized by brightness and tinted by colour index (B−V), so you can tell red giants from blue stars.
• Deep-sky objects use standard atlas symbols: ellipses at true size and position angle for galaxies, circles with crosses for globular clusters, dashed circles for open clusters, squares for nebulae, circles with a ring for planetary nebulae.
• Planets are drawn at their apparent size once it is larger than a dot; Saturn gets its rings.
• Moons of Mars, Jupiter, Saturn, Uranus, Neptune and Pluto appear when the field is narrower than 3°, at their current places around the planet (see Planets' moons). Click a moon to select it, as any other object.
• The Moon is drawn with its correct phase and orientation; the Sun at its true size.
• Comets are drawn with a short tail pointing away from the Sun, asteroids as small crosses, both labelled when bright enough or when you zoom in. They come from the installed MPC files, the four built-in asteroids, and anything you added in the Solar system workspace.
• Milky Way is shaded along the galactic plane at night.
• Telescope position is a crosshair at the connected mount's current pointing.
• In planetarium mode during the day, the sky is coloured by the Sun's altitude and fainter stars fade out, as in reality.
• Your horizon profile from Settings → Location is drawn as part of the ground.

Planets' moons

The chart has 65 moons of the planets:

Planet	Moons
Mars	Phobos, Deimos
Jupiter	Io, Europa, Ganymede, Callisto, Amalthea, Thebe, Metis, Adrastea, Himalia, Elara, Lysithea, Leda, Pasiphae, Sinope, Carme, Ananke
Saturn	Mimas, Enceladus, Tethys, Dione, Rhea, Titan, Hyperion, Iapetus, Phoebe, Janus, Epimetheus, Helene, Telesto, Calypso, Atlas, Prometheus, Pandora, Pan
Uranus	Miranda, Ariel, Umbriel, Titania, Oberon, Cordelia, Ophelia, Cressida, Desdemona, Juliet, Puck
Neptune	Triton, Nereid, Proteus, Larissa, Galatea, Despina, Thalassa, Naiad, Halimede, Sao, Laomedeia, Psamathe, Neso
Pluto	Charon, Nix, Hydra, Kerberos, Styx

• A moon is drawn as a dot sized by its brightness, with its name once it is clear of the planet. It is left out while it is too close to the planet to tell apart and while it is hidden behind it; a moon crossing the disc is drawn dimmer.
• With Deeper when zoomed in ticked (the default), every moon is drawn once it is clear of its planet, however faint. With it unticked, the classical moons (the Galilean moons, Saturn's eight largest, Uranus' five, Triton, Phobos, Deimos and Charon) are always drawn and the others down to two magnitudes fainter than the chosen limit. A moon you select or search for is always drawn.
• Searching for a moon centres it and zooms in until the moon and its planet are both in view and apart.
• Positions come from orbits fitted to JPL's ephemerides and are within 3″ of JPL Horizons from 2000 to 2050, most within 1″. Outside those years the regular moons stay close and the irregular outer moons are rough; see Algorithms and accuracy.

Object information panel

Click any object to select it. The panel shows its name and type, and these buttons:

Button	Action
Center	Centre the chart on the object
Slew	Slew the connected telescope to it
Add to list	Add it to the active observing list in the Planner
Frame	Open it in Astrometry → Framing & mosaics
Copy	Copy its name and coordinates to the clipboard

The details include, as applicable:

• rise, transit (with altitude) and set times, or "circumpolar" / "never rises",
• predicted visibility with your instrument (for example "Easy, margin +2.1 mag"), the best magnification and the sky brightness at the object's position,
• magnitude, size, J2000 and apparent RA/Dec, altitude and azimuth, airmass and hour angle,
• for stars: B−V and temperature, spectral type, distance from parallax, HIP and HD numbers, variability,
• for deep-sky objects: morphology, surface brightness, other names,
• for planets: distance, illuminated fraction, phase angle, elongation, apparent size, and central meridians (Jupiter's systems I, II and III; Mars, Saturn and Venus central meridian, sub-Earth latitude and pole angle),
• for the Moon: age in days,
• for the planets' moons: where it is around its planet (how far east or west, in arcseconds or arcminutes and in planet radii, and whether it is in front, behind, crossing the disc or hidden), distance, diameter and apparent size, and orbital period, marked retrograde for moons that orbit against the planet's spin, such as Triton. Rise, set and the altitude graph are the planet's,
• for comets and asteroids: distance from Earth and Sun, elongation, phase angle and orbit type.

The Altitude tonight graph below shows the object's altitude through the night, with the dark period shaded and a marker at the current time.

Right-click menu

Right-clicking the chart shows the coordinates under the cursor and offers:

• Select and Add … to observing list for the object under the cursor,
• Center here,
• Slew telescope here,
• Frame with camera here.

Controlling the telescope

With a mount connected (see Observatory and devices), Slew or Slew telescope here converts the J2000 position to the apparent position of date and sends the mount there. The telescope crosshair shows where the mount is pointing and moves with it.

Watch the mount when you slew, especially the first time, and make sure cables and the tube cannot hit the pier.

Changing the time

The toolbar has the time controls:

Control	Action
⏪	Back one day
◀	Back one hour
Now	Return to live time
▶	Forward one hour
⏩	Forward one day
Play	Animate time at 300× (one hour every 12 seconds)
Date field	Type a local date and time and press Enter

Changing the time here changes it for the whole program; see Time.

Printing finder charts

Click the printer button to open a print preview of the current view. The printed chart:

• uses a black-on-white print palette that saves ink and reads well under a red torch,
• is rendered at three times screen resolution for crisp output,
• is printed in landscape with a title (the selected object's name), the date and time, site, field of view, limiting magnitude and orientation (normal or mirror view),
• has a legend of the symbols used,
• includes field-of-view circles and rectangles, comets and asteroids, and any mirror or invert setting.

Typical use: select the target, choose Finder (5°) for a finder chart and Eyepiece for a detailed chart, switch to Atlas mode, set mirror or invert to match your telescope, and print both.

Exporting images

The save button writes the chart as a PNG at twice the screen resolution, in the current colours.

Commands

The command palette (Ctrl+K) includes Sky: planetarium mode, Sky: atlas mode, Sky: look north, Sky: look south, Sky: zenith and Sky: print finder chart.