Long-Distance Observations are a type of visual or photographic observation of landscapes that encompass objects visible from distant distances, which can also be seen up close.

The observed object is an inanimate material object. It can be a natural object (e.g., a mountain, hill) or an anthropogenic one (e.g., a mast). An observatory can refer to any point, object, place, or space from which long-distance observations are made.

Depending on the configuration of two elements: the observer’s or observatory’s location and the observed object, the following types of long-distance observations can be distinguished:

A. GROUND-BASED. This is the most common type of observation, encompassing the broad landscape of the Earth, including both natural elements and those created by humans that are permanently connected to the Earth’s surface. For an observation of this type to occur, the observer or recording equipment must also be on the Earth’s surface or on an object permanently connected to it.

Natural elements include: -> Mountain ranges and mountain ranges -> Isolated peaks or hills -> Plant cover (referring to free-standing tall trees that make a particular object recognizable) -> Elements of inanimate nature that make a particular object recognizable from a considerable distance away.

Artificial objects include: -> Elevations made from mining spoil heaps and mining areas that have contributed to a permanent change in the local landscape. -> Various aviation obstacles, including television towers or chimneys. -> Cell phone masts -> Skyline (panoramas of large cities) and individual skyscrapers

B. GROUND-TO-AIR. This refers to situations in which the observer or recording equipment is on Earth or an object permanently connected to its surface and is observing a distant object located in the lower part of Earth’s atmosphere. In this way, distant balloons, airplanes (with the exceptions mentioned earlier), and other objects can be observed.

C. AERIAL. These observations relate to situations in which the observer or recording equipment is not connected to the Earth’s surface. However, the primary purpose of airborne observations is to see an object located on the Earth’s surface or permanently integrated with it. The specificity of airborne observations lies in their diversity depending on the change in the observer’s or equipment’s altitude. The main reason for this is the decreasing contrast between the sky and the horizon as you ascend. As a result, at altitudes of several kilometers, the horizon is practically invisible. Another factor is the reversal of contrast between the distant horizon and the sky, as well as a significant decrease in air density, resulting in reduced light scattering. In practice, the observer cannot see an object hundreds of kilometers away, except when the object is at a similar altitude to the observer and is brightly lit with a high albedo (e.g., the snow-covered peaks of the Himalayas).

D. AIR-TO-AIR  a specific type of long-distance aerial observation in which both the observer, recording equipment, and the observed object are in the air. Such observations can take place, for example, from the cockpit of an airplane observing another airplane from an extremely long distance.

E. EXTRATERRESTRIAL – for which both land and airborne observations within the atmosphere of a given planet can be included. Several such observations from Mars are known.


According to the above definition, Long-Distance Observations DO NOT INCLUDE:

-> Celestial bodies – because they are always far from the observer by definition. Astronomy deals with their observation, and astrophotography documents them.

-> Artificial satellites – which are also a subject of astronomy or astrophotography because these objects orbit the Earth at a considerable altitude far above the Earth’s atmosphere.

-> Aircraft (Plane) spotting – a hobby involving the observation of airplanes under the assumption that the plane is either on the airport tarmac and observed up close or flying high in the sky. Planespotting may become a part of astrophotography when an airplane passes at a small angular distance from a celestial body, especially when it transits the Sun or the Moon. The exception that qualifies planespotting as a form of long-distance observation is only during sunrise or sunset when an airplane is currently transiting against the backdrop of the Sun or the Moon. Due to the very low angular height of the airplane and its great distance from the observation point, it is practically imperceptible in any other way.

-> Clouds – because they are elements of weather that significantly influence the conditions for long-distance observations. This also includes clouds generated by humans, such as Wilson clouds.

-> Contrails – except for the freshest ones directly in contact with the aircraft engine. These often indicate the presence of an airplane observed from a long distance.

-> Shadows of distant mountains – whose presence is determined by the atmospheric conditions at a given moment (the degree of atmospheric pollution and cloud cover).

-> Twilight rays – which indicate the presence of clouds at extremely long distances from the observer.

-> Condensation clouds – produced by industrial objects. They form the basis for the development of clouds or fogs within the planetary boundary layer.

-> Smoke plumes – resulting from fires or wartime activities. This element shapes the local atmospheric conditions for long-distance observations, mainly by reducing atmospheric transparency.

-> Animals (Animal spotting) – because their movements are difficult to predict compared to balloons or airplanes.

-> Urban light pollution – the best example of sky pollution caused by artificial light. At night, it negatively affects long-distance observations.

Long-Distance Observations MAY PARTIALLY INCLUDE:

-> Rockets launching into space – only when the observed object is in the lower part of the Earth’s atmosphere up to the height of the ozone layer.

Ground-based vs. Aerial Observations – the boundary criterion based on the use of drones and other flying objects

Groudn-based Observations INCLUDE: -> Observations of objects made using a drone placed on an object permanently connected to the Earth’s surface only when access to the object is unavailable or dangerous (posing a risk to the observer’s health or life). The observer must be directly under the object on which the drone is placed or as close to it as possible. -> Observations of objects made using a drone located in the immediate vicinity of the object, where the distance of the device from the object:

  • does not exceed the arm span of an adult (Armspan),
  • does not exceed the height of the object when it is impossible or legally prohibited to place the drone on the object.

Ground-based Observations DO NOT INCLUDE: -> Observations of objects made with drones, both when the drone is placed on the object and in the immediate vicinity of the object when the observer is located at a significant distance from the object. A significant distance from the object should be understood, among other things, as a situation in which a person sends a drone to the target observation location instead of being physically present at the location.

For example, a person wants to observe the distant horizon from the Skrzyczne tower using a drone but chooses to operate it from Szczyrk, a location quite far from the tower.

-> Observations of objects made from a balloon (or parachute, paraglider) flying within the height range corresponding to local terrain obstacles. Terrain obstacles should be understood as objects with a height of about 30-35m. Even though they are densely distributed, due to parallax, the view of the distant horizon from their level may not correspond to what is offered by the object itself.

Criteria for the Altitude of Long-Distance Aerial Observations

In principle, two altitude limits for which airborne observations could be considered are contemplated. The first is the boundary of the upper troposphere – the lowest layer of Earth’s atmosphere where about 4/5 of all weather phenomena occur. At this altitude, the conditions between the observer or equipment and the observed object are most similar to those of land observations. However, they change drastically with altitude.

The second crucial barrier is the ozone layer surrounding the Earth’s surface at an altitude of about 40 km. The fundamental criterion for choosing this altitude range is the presence of the Venus Belt, beyond which the Earth’s shadow is directly visible. At the very least, the Venus Belt, best seen shortly after sunset, corresponds to the height at which the horizon is lowered by exactly 6 degrees. You can demonstrate this by looking at the sky just after the end of civil twilight, marked by the Sun being 6º below the horizon. At this moment, the sky is exactly divided into an illuminated and a shaded part (by the Earth’s shadow). When this value is applied to the formula for lowering the horizon, taking into account the standard refractive index, the height above the Earth’s surface is approximately 40 km. It’s also worth noting that above this boundary, the sky during the day is entirely black. Above this boundary, observations become a matter of astronomy and astrophotography.

Criteria for the Reliability of Long-Distance Aerial Observations

Observers are required to provide precise coordinates of the observation location and time if commercial flights are considered. Knowing the location of the aircraft at the time of the photo allows for easy determination of the distance to the observed object. This information can be obtained from websites like Flightradar24.com with a Playback feature and Flightaware.com, which provides a free alternative for periods longer than 7 days.

Depending on aesthetic aspects, long-distance observations can be divided into:

-> Visible – where the primary criterion is merely seeing the object. In this case, minimal contrast of the object against its background is sufficient for it to be noticeable to the human eye or, alternatively, in post-processing. Image processing to achieve tangible results is allowed because it serves as scientific material, e.g., for the analysis of atmospheric refraction phenomena. The mere „appearance” of an object where it theoretically shouldn’t be is a crucial element.

-> Detailed – where the observer can distinguish details of the object’s surface, such as areas covered in snow or slopes covered in forests. The ability to distinguish different types of surface covering on the observed object provides significant benefits for studying atmospheric transparency.

-> Transparent – characterized by the highest quality of the observed object, where the majority of its features are clearly visible. For example, observing the Tatra Mountains from the Bieszczady region during winter, where an observer can identify major gullies and even spot a hotel on top of Lomnica Peak. Such observations provide valuable material for scientific measurements of local atmospheric turbulence.

Methods of Recording Long-Distance Observations

In historical times, the primary method of recording long-distance observations was through visual perceptions followed by subsequent descriptions, as mentioned in this article [link].

Currently, the primary means of recording long-distance observations are photographic equipment, including: -> Compact or digital cameras (camcorders) -> Smartphones -> GoPro cameras and other action cameras -> Drones -> Webcams

The most important feature is having zoom capabilities in these devices. In some cases, achieving this can be challenging under standard conditions (e.g., webcam or drone) because it often requires purchasing relatively expensive equipment.

Scientific Applications of Long-Distance Observations

Some of the fundamental scientific applications of Long-Distance Observations include: -> Studying and observing non-standard atmospheric refraction in the context of ongoing climate changes. -> Determining the frequency of turbulence occurrence in the lower atmosphere and its impact on air traffic. -> Analyzing periodic changes in atmospheric transparency and trends related to air pollution. -> Exploring the psychology and perception of the human eye. -> Assessing the potential of tourist destinations where distant views become common due to increased awareness among local populations (due to the rising popularity of long-distance observations).