Nokto offers three main views: the sky map, a menu on the left that allows the user to set observation parameters, and a detailed information screen that can appear above the sky map.

Sky map

The sky is represented as it can be seen at the date and from the location you specify in the configuration menu. For a better clarity, Nokto favours a cartographic representation over a realistic one.

The map displays the following objects. Note: deep sky objects (galaxies, nebulae, etc.) are mostly invisible to the naked eye and Nokto does not display them unless the relevant option is checked in the configuration menu.

• Planets of our solar system (Mercury, Venus, Mars, Jupiter, Saturn, Uranus and Neptune) are figured by small discs surrounded by a circle. Each planet is identified by a particular colour.
• The Sun is figured by a yellow disc surrounded by a halo.
• The Moon is displayed according to its actual phase: crescent, first or third quarter, gibbous or full.
• Stars are figured by small bright dots. The dot diameter approximately indicates the star luminosity while its colour indicates its spectral type, from light blue for hotter stars to light red for colder ones.
• Galaxies are figured by small red ellipses. For bigger ones, such as M31, the orientation of the ellipse on the map reflects the real orientation in the sky.
• Planetary nebulae are figured by small yellow targets.
• Globular clusters are figured by yellow discs crossed out in black.
• Open clusters are figured by dotted circles.
• Diffuse nebulae are figured by transparent green discs.

Only a few gestures are necessary to control the sky map.

• Pan with one finger to move the sky map. While panning, a compass rose and a clinometer appear at the bottom and the right of the screen respectively, to indicate the direction you are looking to.
• Pinch to zoom: tap the screen with two fingers and spread them apart to zoom in, or move them closer to zoom out. At minimum zoom level, the screen is about 30° wide. At maximum zoom level, it is 5° wide.
• To get detailed information on an object, tap and hold the screen: a magnifying glass appears that lets you precisely point the desired object. Once an object is selected, release to display the detailed information screen.
• If your iPhone is equipped with motion sensors and a compass, shake it to start the VR mode: Nokto automatically determines your orientation in space and displays the sky map accordingly. Tapping anywhere on the screen exits this mode.

Menu

The menu allows you to change date, time and location of observation, as well as various display options. To access it, touch the button on the left edge of the sky map. Touch the same button again to close it, or swipe left. Most options among those available are straightforward and are not further described here.

When the Set automatically switch is on, the device automatically determines the date, time zone and location of observation. However, if your device is not equipped with a GPS, or if you want to know what the sky looks like from another location or at another date than your actual ones, you can disable this setting and manually change observation parameters.

Valid range for the date of observation is January 1st, 1900 to December 31st, 2037. Allowing more distant dates in the past or in the future would impact accuracy: for performance reasons, Nokto uses a simplified theory of planetary movements that gives a lower precision when date is too far away from mid-twentieth century.

The Star slider adjusts the number of stars on the sky map. When set in right position while the map is zoomed at maximum level, Nokto displays stars up to magnitude 9, which means about 182,000 stars.

Deep sky objects are nebulae, galaxies and clusters. Most of them are invisible to the naked eye, so Nokto does not display them by default. You can however enable this option to make them visible on the map, for example if you are looking for information on a specific object or if you are observing the sky with binoculars.

By default, coordinates of solar system objects are corrected for parallax: their apparent position on the sky is corrected to take your actual location on Earth into account. You can however disable this option if you need geocentric coordinates, for example for comparison purposes with other sources. In this case, position of the moon and the nearest planets will be slightly wrong.

Information screens

Tapping on the search bar at the top of the main screen displays a list of major astronomical objects. Selecting an item in this list brings you to a detailed information screen where you can find object size, magnitude, equatorial coordinates (right ascension and declination), rising and setting times, and so on.

Entering characters in the search bar filters the displayed list. The whole catalogue is searchable but for the sake of performance, only the brightest astronomical objects are displayed initially. You can search objects by:

• Part of their usual or Latin name. For constellation, you can also search by abbreviated names.
• Bayer catalogue, for example: α UMi or δ Scu. (To enter Greek letters, enable the Greek keyboard in the Settings application of your iPhone.)
• Flamsteed catalogue, for example: 57 Dra.
• SAO catalogue, for example: SAO 139209.
• Messier catalogue, for example: M 31.
• NGC catalogue, for example: NGC 7000.

Search is insensitive to case and diacritics. The Deep sky option in the menu must be enabled if you are searching for deep sky objects.

Tapping the Cancel button on the right of the search bar exits the search mode.