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This simulator uses a complex program that interprets data from satellite imagery to calculate a realistic 'sky-view' for any location in the UK. The circular 'sky-view' is an inner-dome image similar to a planetarium view. The sky-view shows how the real sky would appear to a ground based observer when looking up. The zenith overhead is shown in the center and the horizon around the edge.

On the map, the center point of the moveable target shows the observation point. The target arrow points toward the compass direction the observer is facing. This direction is shown in the lower part of the 'sky-view'. Pressing the '< >' buttons will rotate this view point.

Distant towns will appear realistically as domes of light on the horizon. If the 'sky-view' is bright with fewer stars visible, this indicates 'sky-glow' from a large town nearby, or from viewing within an urban area.

The 'Bortle dark sky scale' (top of simulator) gives the observation area an approximate dark-sky rating from 1(best) - 9(worst).

Press the 'render clouds' button to display clouds. Clouds are reflective and can appear very bright in the presence of light pollution. Conversely, from a good dark site, clouds will appear much darker overhead, sometimes only visible as gaps in the stars!

Questions and Answers

Q. What is that cloud-like band across the sky?

A. The cloud is millions of distant stars which form the Milkyway, our surrounding galaxy!

If you haven't seen it in the night sky before, you may live in an area that is badly affected by light pollution. It is well worth traveling to a darker area to observe this truly amazing sight.

Q. The 'sky-view' seems exaggerated, can sky-glow or the Milkyway really look that bright?

A. The generated 'sky-view' is designed to show up clearly on all monitors under varying room lighting, the brightness and contrast are therefore set quite high. However, if we consider how our perception of the night sky changes as our eyes adapt to the dark, the generated view is actually quite close to what we see. To a 'dark-adapted' observer, sky-glow will appear much brighter around urban areas and from a truly dark site, the Milkyway will appear very bright too. This is because the eyes can become fully dark-adapted and very sensitive to the light.

Please note: Due to a number of factors beyond the scope of this simulator, the observed conditions may differ from the calculated 'sky-view'. These factors include....

The eyesight of the observer.

Allowed time for dark adaption of the eyes. Any directly visible light sources will prevent good dark adaption of the eyes.

The atmospheric visibility and weather. The darkest and starriest nights often follow deep blue skies, not gray or hazy skies.

The time of Day. This seems obvious but although it may seem fairly dark after sunset, it is not as dark as it can get until the time of 'astronomical night' is reached.

The Moon if present will produce a lot of 'natural' sky-glow and glare, especially around full moon.

Local Light Pollution may be created by smaller towns which are are unresolved by map. If possible, observe from areas shaded or away from nearby light sources.

The orientation and visibility of the stars and Milkyway may differ from what is shown as this depends on the location and time.

The satellite data used to create the 'sky-view' is from 2000. It is estimated that light pollution is far more widespread now than is shown by the simulator. New satellite data will be used to improve the accuracy of this simulation if it becomes available.