The Stellarium software offers a bunch of useful options for rendering the sky view in light of different cultures. The best ground-breaking option introduced a while ago is the ShowMySky mode for rendering the true atmosphere, about which I wrote in this article. It’s not everything! As I came to another function, an inherent rendering feature of this mode – the changes in Earth’s atmospheric appearance as it occurs with the altitude. Initially, the option can be found in the Current location information, below the selection of Latitude and Longitude (Pic. 1).
By default, the Elevation is set to 0 m, which corresponds to sea level. It doesn’t change if your location is defined manually. In other cases, all the places have the altitude value defined (Pic. 2), but at first glance, the elevation value remains meaningless as the horizon line, along with the horizontal grid, doesn’t change (Pic. 3).
This situation makes the elevation adjustment unimportant. The position of the local horizon, as well as the horizontal grid, remains the same. The only changes are noticeable in the rendered sky. It’s too few changes to make this a helpful option. However, this article aims to demonstrate how this particular Stellarium feature can become useful!
Let’s start with the easy thing, which will help us to understand this task. The horizontal grid is toggleable, unlike the horizon, which can be set at most as transparent (Pic. 4).
Even so, the view seems to look troublesome, as the celestial sphere is mirrored below the horizon line (Pic. 5). The rendered haze density and atmosphere thickness quite clearly mark this line as the best visible during the sunrise or sunset.
Despite dramatic elevation changes, the horizon line and the entire azimuthal grid system remain in place and still correspond to the sea level. The mirrored sky below the horizon makes the horizon line difficult to identify at the defined elevation. An observer can guess its position based on the zone of greatest atmospheric thickness indicated by different coloration; however, he will never be confident enough to determine exactly where the horizon is. For this reason, we need to use the snazzy, although hidden, option in Stellarium, which will seriously facilitate an observer’s getting around. We need to enter the Sky options (Pic. 6) and head to the Atmosphere visualization section, where you will find the screw key icon.
Once clicked, the Atmosphere Details window opens, where you will find the Show debugging options turned off by default (Pic. 7).
Turning on the Show debugging options expands the additional choices, among which we can notice “Mirror the sky under the horizon” as the last one. Because it’s initially turned on, our sky is always mirrored below the horizon line. This is where our problem comes from. By unthicking this option, we accommodate ourselves to the real outdoor conditions as would be observed at the specified altitude (Pic. 8 – 10).
The final image above shows the projection of the horizon at various altitudes. The leftmost shot shows the ground-based horizon projection for Rzeszów (209m.a.s.l.), next the view of the horizon from the highest Tatra Mountains summit – Gerlach (2655m.a.s.l.), and another one represents the view from cruising altitude (10000m.a.s.l.) and the last one an estimated horizon to be seen from the meteorological balloon’s perspective at 30000m above the sea level.
There is an essential point to mention: all these visualizations are devoid of cloud coverage! Everyone has to keep in mind that the cloud deck will obscure the estimated horizon line at random elevation. We need to include this kind of margin when planning an elevated observation.
Mariusz Krukar
Links:
Forums:
- https://www.cloudynights.com/forums/topic/928365-stellarium-doesnt-use-elevation-data-for-atmospheric-absorption/
- Github.com: Elevation of observed site
- Sourceforge.net: Stellarium – Position of Horizon on the screen / horizon elevation
- https://www.cloudynights.com/forums/topic/947470-stellarium-mark-specific-altitude-line/
Youtube: