Within A Head On Aircraft Can Look Like A Stationary Light...
The geometry behind the hovering light illusion
When an approaching aircraft keeps nearly the same bearing, it can seem stationary even while its range is shrinking.
On this page
- What constant bearing means for a skywatcher
- Why little sideways motion fools the eye
- How the illusion breaks near the end
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Introduction
A surprisingly common cause of UFO reports is an aircraft approaching almost directly towards the observer. In this geometry, the aircraft can appear to hover in one spot for minutes even while covering many kilometres. The effect is known in navigation and collision studies as constant bearing, decreasing range: the direction to the object changes very little while the distance steadily shrinks. To a skywatcher, the result can be a bright light that seems fixed against the stars, only revealing its true nature much later when it grows larger, changes angle, or passes overhead. Aviation safety research has long recognised this geometry because it creates detection problems for pilots as well as perceptual confusion for observers on the ground. [visualexpert.com]visualexpert.comA Crash Course In Collisions: The CBDR Rule - Marc GreenIn both cases, the bearing angle remains constant and there is no significant ret…
What constant bearing means for a skywatcher
A bearing is the direction of an object relative to an observer. If an aircraft is flying almost directly towards you, its bearing remains nearly unchanged even though its range is decreasing rapidly.
Imagine a jet on a long final approach to an airport. From the pilot’s perspective the aircraft is moving at hundreds of kilometres per hour. From the observer’s perspective, however, the aircraft’s position against the background sky may barely shift. The motion exists mostly along the line of sight rather than across it.
This geometry is well known in aviation and maritime collision analysis. Researchers describe it as a constant-bearing situation in which there is little or no apparent sideways displacement, sometimes referred to as minimal retinal slip because the image does not move significantly across the observer’s retina. [visualexpert.com]visualexpert.comA Crash Course In Collisions: The CBDR Rule - Marc GreenIn both cases, the bearing angle remains constant and there is no significant ret…
For UFO witnesses, that means a bright object can appear unnaturally stationary even though it is travelling at normal aircraft speeds. The visual impression is often strengthened when the aircraft is distant enough that its structure cannot yet be resolved and only its lights are visible.
Why little sideways motion fools the eye
Human vision is exceptionally good at detecting movement across a scene. It is much less effective at judging motion directly towards or away from the observer.
Aviation researchers studying mid-air collision risks have repeatedly noted that an aircraft on a collision course can appear small, motionless and inconspicuous until shortly before impact because its relative bearing remains constant. In other words, the lack of lateral movement deprives observers of one of their strongest motion cues. [PubMed]pubmed.ncbi.nlm.nih.govPubMedlimitations of the see-and-avoid concept in civil aviationby CC Morris · 2005 · Cited by 57 — Because the relative bearing to each…
For someone watching the night sky, several factors amplify the effect:
- No nearby reference points. Against a dark sky there may be nothing with which to compare the object’s position.
- Point-source appearance. At long range an aircraft becomes a bright point rather than a recognisable machine.
- Difficulty judging distance. Humans estimate movement partly through changes in apparent size. A distant light offers very little information about range.
- Attention on brightness rather than geometry. Observers often notice that the light is bright but do not perceive how slowly it is growing larger.
The same underlying geometry that concerns collision-avoidance specialists can therefore generate reports of hovering or stationary unidentified lights. [PubMed]pubmed.ncbi.nlm.nih.govPubMedlimitations of the see-and-avoid concept in civil aviationby CC Morris · 2005 · Cited by 57 — Because the relative bearing to each… [2rnsa.is]rnsa.isMid-Air CollisionsThe pilots of two aircraft flying at a constant speed and altitude and having convergent trajectories will each see the…
Why bright landing lights make the effect stronger
Many head-on sightings involve aircraft using landing lights or other forward-facing lights. These lights are designed to maximise visibility from the front, particularly near airports and in areas of heavy traffic. FAA guidance encourages their use to improve the effectiveness of the “see and avoid” principle. [AeroLEDs]aeroleds.comfaa encourages the use of landing lights for increased visibilityAeroLEDsFAA Encourages The Use Of Landing Lights For Increased…12 Dec 2020 — To enhance the “see and avoid” concept, the FAA encourage…
Landing lights are typically intense, narrow-beam white lights aimed forward. When viewed close to their beam axis, they can dominate the observer’s perception while the aircraft itself remains invisible. A skywatcher may therefore see a brilliant white light with no obvious wings, fuselage or navigation lights. [AeroSavvy]aerosavvy.comAeroSavvySavvy Passenger Guide to Airplane LightsLanding lights are the largest, brightest lights on an aircraft. They are typically moun…
The combination of constant bearing and a bright forward-facing light is particularly effective at producing the impression of a hovering luminous object.
How the illusion breaks near the end
The illusion rarely lasts indefinitely. As the aircraft closes the remaining distance, visual cues begin to accumulate.
Several changes commonly occur:
- The aircraft’s apparent size starts increasing more noticeably.
- Navigation lights become easier to distinguish.
- The object may begin to drift sideways as the geometry changes.
- Engine noise may become audible.
- The aircraft may turn, immediately revealing its true motion.
This transition often feels abrupt to witnesses. An object that appeared stationary for several minutes can suddenly seem to “move off” or transform into an obvious aircraft. In reality, the aircraft was moving the entire time; the observer simply lacked enough visual information to perceive that motion earlier.
Collision-avoidance studies describe a related effect in which an object remains visually static for much of the encounter and only produces substantial apparent movement near the final stages. [visualexpert.com]visualexpert.comA Crash Course In Collisions: The CBDR Rule - Marc GreenIn both cases, the bearing angle remains constant and there is no significant ret…
Why this explanation fits many UFO reports
The constant-bearing explanation is supported by well-understood geometry rather than speculation. It is consistent with decades of aviation safety research showing that approaching aircraft can appear motionless when their bearing remains unchanged. Researchers studying mid-air collisions have specifically highlighted the tendency of collision-course aircraft to seem stationary until very late in an encounter. [PubMed]pubmed.ncbi.nlm.nih.govPubMedlimitations of the see-and-avoid concept in civil aviationby CC Morris · 2005 · Cited by 57 — Because the relative bearing to each…
In UFO reporting, the same mechanism helps explain recurring descriptions such as:
- A bright light that appeared fixed in one position.
- An object that seemed to hover without obvious propulsion.
- A stationary light that suddenly became an aircraft.
- A light seen near an airport approach path.
- An object that showed little movement until the final moments of observation.
The key point is that the appearance of hovering does not necessarily imply that an object is actually stationary. Under constant-bearing geometry, a normally operating aircraft can create exactly that impression, making this one of the most important mechanisms behind reports of apparently motionless lights in the sky. [visualexpert.com]visualexpert.comA Crash Course In Collisions: The CBDR Rule - Marc GreenIn both cases, the bearing angle remains constant and there is no significant ret… [PubMed]pubmed.ncbi.nlm.nih.govPubMedlimitations of the see-and-avoid concept in civil aviationby CC Morris · 2005 · Cited by 57 — Because the relative bearing to each…
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Endnotes
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Source: visualexpert.com
Link: https://www.visualexpert.com/Resources/crashcourse.htmlSource snippet
A Crash Course In Collisions: The CBDR Rule - Marc GreenIn both cases, the bearing angle remains constant and there is no significant ret...
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Source: rnsa.is
Link: https://www.rnsa.is/media/1931/midair-collisions.pdfSource snippet
Mid-Air CollisionsThe pilots of two aircraft flying at a constant speed and altitude and having convergent [trajectories]({{ 'trajectories/' | relative_url }}) will each see the...
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Source: aeroleds.com
Title: faa encourages the use of landing lights for increased visibility
Link: https://aeroleds.com/blogs/news/faa-encourages-the-use-of-landing-lights-for-increased-visibility?srsltid=AfmBOook3NOaVHSTh_MjvDYsP9F8ek5-wJgtF4AF8p7OTvmNtqtB_9OUSource snippet
AeroLEDsFAA Encourages The Use Of Landing Lights For Increased...12 Dec 2020 — To enhance the “see and avoid” concept, the FAA encourage...
-
Source: aerosavvy.com
Link: https://aerosavvy.com/airplane-lights/Source snippet
AeroSavvySavvy Passenger Guide to Airplane LightsLanding lights are the largest, brightest lights on an aircraft. They are typically moun...
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Source: faa.gov
Link: https://www.faa.gov/sites/faa.gov/files/regulations_policies/handbooks_manuals/aviation/airplane_handbook/12_afh_ch11.pdfSource snippet
der certain conditions, approach lights can make the aircraft...Read more...
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Source: faa.gov
Title: Chapter 2
Link: https://www.faa.gov/Air_traffic/publications/atpubs/aim_html/chap2_section_1.htmlSource snippet
Aeronautical Lighting and Other Airport Visual...The lights marking the ends of the runway emit red light toward the runway to indicate...
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Source: faa.gov
Link: https://www.faa.gov/documentlibrary/media/advisory_circular/ac_90-48d_chg_1.pdfSource snippet
AC 90-48D CHG 119 Apr 2016 — Statistics indicate that the majority of these midair collisions and. NMACs occurred in good weather and dur...
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Source: pubmed.ncbi.nlm.nih.gov
Link: https://pubmed.ncbi.nlm.nih.gov/15828635/Source snippet
PubMedlimitations of the see-and-avoid concept in civil aviationby CC Morris · 2005 · Cited by 57 — Because the relative bearing to each...
Additional References
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Source: reddit.com
Link: https://www.reddit.com/r/flightsim/comments/16e01hk/correct_use_of_external_lights/Source snippet
Correct use of external lights: r/flightsimPresumably this is to increase visibility so that if there was an aircraft on approach they'd...
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Source: linkedin.com
Link: https://www.linkedin.com/posts/rogerhall-lxm_faa-introduces-new-runway-status-lights-system-activity-7309473077195681792-udbUSource snippet
FAA introduces Runway Status Lights to prevent collisionsThe FAA's RWSL system is designed to help prevent runway incursions by providing...
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Source: skybrary.aero
Link: https://skybrary.aero/articles/midair-collisionSource snippet
Midair CollisionContributory Factors · Traffic conditions. This includes the traffic density, complexity, mixture of aircraft types and c...
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Source: medium.com
Link: https://medium.com/faa/mitigating-the-hazard-of-visual-illusions-fb3c35009471 -
Source: aopa.org
Link: https://www.aopa.org/training-and-safety/students/crosscountry/skills/night-flyingSource snippet
Night FlyingA string of lights across the canvas of night can appear as a horizon. Rolling your wings level to such an illusion can place...
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Source: researchgate.net
Link: https://www.researchgate.net/publication/7907700_Midair_collisions_Limitations_of_the_see-and-avoid_concept_in_civil_aviationSource snippet
Limitations of the see-and-avoid concept in civil aviationMidair collisions cause loss of life and property and undermine general aviatio...
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Source: reddit.com
Link: https://www.reddit.com/r/aviation/comments/1iehq93/why_would_pilots_turn_landing_lights_on_and_off/Source snippet
Why would pilots turn landing lights on and off?: r/aviationOn ground: Taxi lights ON when the plane is moving and OFF when stationary(e...
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Source: researchgate.net
Link: https://www.researchgate.net/publication/309818544_Detection_of_Airborne_Collision-Course_Targets_for_Sense_and_Avoid_on_Unmanned_Aircraft_Systems_Using_Machine_Vision_TechniquesSource snippet
Detection of Airborne Collision-Course Targets for Sense...2 Nov 2016 — Detecting collision-course targets in aerial scenes from purely...
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Source: reddit.com
Link: https://www.reddit.com/r/aviation/comments/1hz2b1m/exterior_aircraft_lights/ -
Source: youtube.com
Link: https://www.youtube.com/watch?v=zDbmBM9YG_0Source snippet
APPROACH LIGHTING SYSTEMThe approach lighting is a part of a system aimed to give to an approaching aircraft the required information for...
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