In astronomy, how bright an object appears to an observer is called the object's apparent (visual) magnitude, and is denoted in SpaceEngine by m. Magnitude values follow an inverse logarithmic scale; the lower the value, the brighter the object, and a decrease of 5 magnitudes equals an increase in brightness of 100 times. The dimmest stars visible with the naked eye from very dark skies on Earth have a magnitude around 6-7m, and the brightest stars have a magnitude less than 1m; the brightest star, Sirius, has a negative magnitude: -1.44m. The sun as seen from Earth has a magnitude -26.7m.
The limiting magnitude for any light-receiving device (like an eye or a camera) is the magnitude of the faintest objects than can be registered by the device. The limiting magnitude of the unaided human eye is 6-7m, while the most capable ground-based telescopes can detect objects up to 28m. SpaceEngine has an option to increase the limiting magnitude, similar to the naked eye having super-sensitive vision, thus making it possible to see more stars and other celestial objects more clearly. This is the only way to see distant galaxies and nebulae at their best.
Information about the limiting magnitude is displayed in the lower-right corner of the screen «Limit: 7.m00». If the limiting magnitude for all objects is the same, only one value will be displayed. If galaxies, stars, and planets each have different settings, then the current value for each will be displayed independently.
Magnitude and lighting settings can be adjusted in the Magnitude/brightness settings menu, which can be opened by pressing [F7], or by clicking on the gear icon on the lower-right toolbar. You can change the limiting magnitude for all objects by pressing the '[' and ']' keys, or by using the buttons on the lower-right toolbar. To change the limiting magnitude value for planets, stars, and galaxies/nebulae/star clusters separately, use the menu shown above, or press the '[' and the ']' keys while holding down [Shift] for galaxies/nebulae/clusters, [Ctrl] for stars, or [Ctrl]+[Shift] for planets. Values can be reset to default by pressing the Default button in the magnitude limit section of the menu, or by pressing the button on the lower-right toolbar.
Increasing the limiting magnitude to large values will lead to a reduction in PC performance.
The checkbox for [Auto increase galaxies magnitude] enables the automatic increase of the limiting magnitude of galaxies up to 16m while the camera is in intergalactic space. This allows for easier visual navigation among galaxies and obseration of the larger scale structure of the universe.
The overall brightness of the scene can be changed by adjusting the exposure setting, the brightness of galaxy and nebula models can be changed using the glow magnitude limit setting, and uniform white light, called ambient light, can be used to illuminate planets and spacecraft; this is especially useful for viewing the dark sides of planets.
Exposure can be increased or decreased by using the slider in the menu, the buttons on the lower-right toolbar, or the [<] and [>] keys. The glow magnitude limit can be changed by using the galaxies model lighting slider in the menu, or by using the [Ctrl]+[<] and [Ctrl]+[>] keys. The ambient light level can be changed by using the slider in the menu, or by using the [Shift]+[<] and [Shift]+[>] keys. Exposure can be reset to default by using the button on the lower-right toolbar, and all values can be reset by pressing the Default button in the models lighting section of the menu.
For information about the Overbright and Desaturate dim stars options, see Graphics.