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Why Stars Flash Like Machines

Low stars can flash red, green and white as atmospheric turbulence bends their light across the horizon.

On this page

  • Scintillation near the horizon
  • Cloud cover and sudden vanishing
  • Common star identification mistakes
Preview for Why Stars Flash Like Machines

Introduction

A bright star low in the sky can look surprisingly artificial. It may flash red, green, blue and white; pulse like an aircraft beacon; seem to jerk or hover; and then vanish when a patch of cloud, haze or a roofline crosses it. In UFO reporting, this is one of the simplest ways a real observation becomes a puzzling story: the witness is not inventing the light, but the atmosphere is making a distant star behave unlike the steady point they expected.

Overview image for Stars The mechanism is called scintillation, or twinkling. Starlight passes through moving layers of air with different temperatures and densities, and those layers bend and scatter the light before it reaches the eye. The effect is strongest near the horizon, where the light has to travel through much more atmosphere than it would overhead. NASA’s StarChild education material makes the same practical point: stars near the horizon twinkle more because there is more atmosphere between the observer and the star. [StarChild]starchild.gsfc.nasa.govStar Child Why do stars twinkle?Star Child Why do stars twinkle?

Sirius example of atmospheric turbulence

Channel: Blackrock Castle Observatory

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Why Low Stars Flash Like Machines

The key to this kind of IFO is that stars are effectively point sources of light. They are so distant that, to the naked eye, their light arrives from an extremely tiny apparent point. A small moving pocket of turbulent air can therefore bend much of that point’s light away from the eye, then back again, making the star brighten, dim, shift slightly or split into flashes of colour. The European Southern Observatory describes the same turbulence as the reason stars twinkle and as a serious problem for ground-based astronomy, because it blurs fine detail in telescope images. [ELT ESO]elt.eso.orgELT ESOAdaptive Optics | ELTELT ESOAdaptive Optics | ELT

The colour-changing part is especially important for UFO reports. Starlight contains many colours. As it crosses uneven air, refraction can separate and redirect those colours by tiny amounts. Near the horizon, the light path is longer, lower and more disturbed, so the observer may see rapid red, green, blue and white flashes rather than a steady white point. EarthSky’s explanation of Sirius notes that this bright star often appears to flash different colours when low in the sky, because the atmosphere breaks starlight into its component colours and the effect is much more obvious when the star is seen through a thicker layer of air. [EarthSky]earthsky.orgEarth Sky Flashing star in autumn? Here are 3 candidatesEarth Sky Flashing star in autumn? Here are 3 candidates

This can look mechanical because human perception is good at turning irregular flashes into implied patterns. A star that alternates white-green-red-white may be interpreted as a craft with navigation lights. A very bright star seen through restless air may seem to “signal”, “pulse”, “rotate” or “change shape”. Atmospheric optics specialist Les Cowley’s Atmospheric Optics site gives a useful refinement: some of the changing brightness and colour in a scintillating star can come from moving caustic patterns, similar to the bright rippling lines seen on the bottom of a swimming pool. [At Optics]atoptics.co.ukAt Optics OPODAt Optics OPOD

Sirius is the classic culprit because it is the brightest star in the night sky and often sits low enough to shimmer violently from mid-northern latitudes. Universe Today has called Sirius a “UFO trickster” for exactly this reason: it is bright, low, slow-moving across the sky, and capable of throwing out different colours under poor seeing conditions. [Universe Today]universetoday.comUniverse Today Sirius, UFO trickster extraordinaireUniverse Today Sirius, UFO trickster extraordinaire Capella can play the same role in northern autumn and winter evenings; EarthSky notes that Capella is a bright northeastern star that often flashes red, green and blue when low, prompting UFO questions from Northern Hemisphere observers. [EarthSky]earthsky.orgEarth Sky Flashing star in autumn? Here are 3 candidatesEarth Sky Flashing star in autumn? Here are 3 candidates

Stars illustration 1

Scintillation Near the Horizon

The horizon is where the illusion becomes most persuasive. A star overhead is seen through a relatively short column of air. A star just above the horizon is seen through a long, dense, dirty and turbulent slice of atmosphere, often close to rooftops, trees, warm roads, sea air, hills, smoke, humidity or city haze. That is why the same star can look calm later in the night when it has climbed higher, yet appear like a flashing object when it first rises.

This matters for UFO interpretation because a low star also lacks obvious distance cues. A bright point above a distant treeline might be a star, a drone, an aircraft, a mast light or something on a hillside. In darkness, without a known foreground reference, the brain may place the light much closer than it really is. Once the light is mentally placed nearby, its atmospheric flicker can be misread as the behaviour of an object: hovering, rotating, changing altitude or making abrupt movements.

Astronomers separate two related observing conditions that witnesses often experience together. “Seeing” refers to atmospheric steadiness: poor seeing makes stars shimmer, dance and blur. “Transparency” refers to how clear the air is: poor transparency from haze, smoke, dust or thin cloud dims objects and reduces contrast. Astronomy Magazine describes transparency as the clarity of the atmosphere, affected by clouds, smoke, dust and haze, while seeing concerns steadiness rather than clarity. [Astronomy Magazine]astronomy.comwhat are transparency and seeingwhat are transparency and seeing A night can therefore be clear enough to show a bright star, but unstable enough to make it flash wildly.

The planets provide a useful comparison, but not an absolute rule. Planets usually look steadier than stars because they show a small apparent disc rather than a true point, so atmospheric distortions are averaged across a wider patch of light. Britannica’s explanation of twinkling uses this distinction: stars appear as tiny points more easily disturbed by atmospheric turbulence, while planets generally twinkle less because their small discs average out the distortions. [Encyclopedia Britannica]britannica.comEncyclopedia Britannica Why Do Stars Twinkle? | Stars, Astronomy, & FactsEncyclopedia Britannica Why Do Stars Twinkle? | Stars, Astronomy, & Facts However, a very bright planet low in the sky can also scintillate. EarthSky documents Venus showing multiple colours when very low, even though planets normally shine more steadily. [EarthSky]earthsky.orgEarth Sky Flashing star in autumn? Here are 3 candidatesEarth Sky Flashing star in autumn? Here are 3 candidates

Are Stars Disappearing? With Dr. Beatriz Villarroel

Channel: Event Horizon · Views: 73.1K · Uploaded: January 2020 · Length: 21 minutes

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Cloud Cover and Sudden Vanishing

The “it vanished” part of a UFO report can be just as natural as the flashing. Thin cloud can be hard to notice at night, especially in light-polluted areas where the sky already looks grey. A bright star may shine through a veil of cirrus for a while, dim, flare again through a thinner patch, then disappear completely when a denser part of the cloud crosses the line of sight.

This is different from a star physically going out. The light has simply been blocked or scattered before it reaches the observer. The National Radio Astronomy Observatory gives a direct answer to a common public question about stars repeatedly disappearing and reappearing: the Earth’s atmosphere can bend and block the light from point sources, and thin clouds can make a star fade in and out as they pass overhead. [National Radio Astronomy Observatory]public.nrao.eduwhat causes stars to repeatedly disappear and reappearwhat causes stars to repeatedly disappear and reappear

Cloud-related vanishing can make the sighting feel more anomalous because the observer may not register the cloud as the cause. The rest of the sky may still show stars. The cloud may be visible only as a faint loss of contrast. In a moving patchwork of cloud, one bright star can disappear while others remain visible, especially if they sit in clearer gaps or are higher in the sky.

A typical misidentification sequence looks like this:

  • A bright low star is noticed because it flashes several colours.
  • The observer watches it for long enough to perceive slight apparent movement or pulsing.
  • Thin cloud or haze dims it, making it seem to retreat, cloak or power down.
  • A thicker cloud patch hides it completely.
  • When the observer later checks the same direction, the star has moved with the sky or the cloud has changed, so the scene no longer matches the memory.

The suddenness is not evidence of propulsion. It is a line-of-sight effect. A small cloud edge can cross a point-like star quickly, just as a chimney, branch or roofline can make it “switch off” instantly when the observer or the star’s apparent position changes.

Stars illustration 2

Common Star-Identification Mistakes

The most common mistake is assuming that a flashing light must be close. Stars are distant, but their apparent behaviour can look local when seen through unsettled air. A witness may say the light was “above the houses” or “over the field”, when that only describes its direction, not its distance. Without parallax, sound, shadow, a resolved shape or a known object beside it, distance estimates for a single night-time point of light are very unreliable.

Another common mistake is assuming that colour changes mean a machine. Aircraft do have navigation and anti-collision lights, but they also move in relation to the landscape, change angle, show multiple separated lights at close range, and may make sound. A scintillating star usually stays fixed relative to the star field and drifts slowly westward with the sky over minutes to hours. Its “flashing lights” are not mounted lamps; they are atmospheric distortions of one point source.

A third mistake is checking the wrong time or direction afterwards. Star identification depends on date, time, location and bearing. A report that says “a flashing light in the east last night” may be enough to suggest Sirius or Capella in some seasons, but not enough for certainty. The stronger check is to use a sky map for the exact location and time, then ask whether a bright star or planet was near the reported direction and altitude.

The most useful quick checks are practical rather than technical:

  • Hold position against landmarks. A star will keep the same broad place over short periods, then drift slowly with the sky. A drone or aircraft will usually change position much faster against trees, roofs or poles.
  • Compare it with nearby stars. If several stars are twinkling, and the low bright one is simply the most dramatic, atmospheric seeing is the likely driver.
  • Watch it through binoculars held steady. A star remains a point; an aircraft may resolve into multiple lights or a shape.
  • Check whether it rises or sets predictably. A star near the eastern horizon climbs; one near the western horizon sinks. That slow arc is not independent flight.
  • Look for cloud and haze. If other stars fade in the same part of the sky, the “vanishing” is probably atmospheric or cloud-related.

These checks do not prove that every flashing light is a star. They help sort the easy IFOs from cases that deserve more careful comparison with aircraft tracks, satellites, drones, balloons or local lights.

Why Do Stars Twinkle?

Channel: SciShow

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Why This Explanation Matters for UFO Reports

Twinkling stars are a good reminder that UFO reports often begin with genuine observation. The witness really did see a light. It really did flash different colours. It may really have vanished. The identification changes because the context changes: once the star’s position, the horizon angle, atmospheric conditions and cloud cover are considered, the behaviour is no longer extraordinary.

Official and scientific reviews of UFO and UAP reports repeatedly stress this distinction between unexplained at first sight and anomalous after investigation. Project Blue Book’s historical files included astronomical bodies among the ordinary causes of reports, and modern UAP reviews continue to find that many cases resolve into conventional objects or phenomena when better data are available. AARO’s public case-resolution material, for example, shows the same method in another category: apparent anomalies are assessed against ordinary candidates such as balloons, wind drift and performance characteristics. [AARO]aaro.milOpen source on aaro.mil.

The star explanation is strongest when the report has a bright stationary or slow-drifting point low on the horizon, rapid colour flicker, no reliable distance cue, no close-range structure, and a time-direction match with Sirius, Capella, Arcturus, Vega, Jupiter or Venus. It is weaker when the report includes multiple independent viewing angles, radar correlation, resolved structure, nearby interaction, rapid angular travel across a large part of the sky, or behaviour inconsistent with the known sky at that time.

For everyday IFO work, the lesson is simple: before treating a colour-changing light as a craft, identify the sky. Low stars can look like machines because the atmosphere is acting like a restless lens and prism. The stranger the flashing looks near the horizon, the more likely it is that the air, not the object, is doing the work.

Stars illustration 3

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Endnotes

  1. Source: starchild.gsfc.nasa.gov
    Title: Star Child Why do stars twinkle?
    Link: https://starchild.gsfc.nasa.gov/docs/StarChild/questions/question26.html

  2. Source: elt.eso.org
    Title: ELT ESOAdaptive Optics | ELT
    Link: https://elt.eso.org/telescope/adaptiveoptics/

  3. Source: earthsky.org
    Title: Earth Sky Flashing star in autumn? Here are 3 candidates
    Link: https://earthsky.org/astronomy-essentials/flashing-star-autumn-capella-arcturus-sirius/

  4. Source: earthsky.org
    Title: Earth Sky What star in the northeast flashes colorfully? It’s Capella!
    Link: https://earthsky.org/tonight/what-star-in-the-northeast-flashes-red-and-green/

  5. Source: astronomy.com
    Title: what are transparency and seeing
    Link: https://www.astronomy.com/observing/what-are-transparency-and-seeing/

  6. Source: britannica.com
    Title: Encyclopedia Britannica Why Do Stars Twinkle? | Stars, Astronomy, & Facts
    Link: https://www.britannica.com/science/Why-Do-Stars-Twinkle

  7. Source: earthsky.org
    Title: Earth Sky Colors of scintillating Venus | Astronomy Essentials
    Link: https://earthsky.org/astronomy-essentials/colors-scintillating-venus-mar-2017-photos/

  8. Source: aaro.mil
    Link: https://www.aaro.mil/UAP-Cases/Official-UAP-Imagery/

  9. Source: eso.org
    Link: https://www.eso.org/public/spain/news/eso8908/?lang=

  10. Source: eso.org
    Link: https://www.eso.org/public/teles-instr/technology/adaptive_optics/

  11. Source: hq.eso.org
    Link: https://www.hq.eso.org/public/archives/videos/script/esocast34a.pdf

  12. Source: eso.org
    Title: ES Ocast 34: How To Stop a Star’s Twinkle
    Link: https://www.eso.org/public/videos/esocast34a/

  13. Source: eso.org
    Link: https://www.eso.org/projects/aot

  14. Source: eso.org
    Link: https://www.eso.org/public/switzerland-de/blog/twinkle-twinkle-little-star/?lang=

  15. Source: eso.org
    Link: https://www.eso.org/public/videos/cs0018a/

  16. Source: eso.org
    Link: https://www.eso.org/public/italy/news/eso9006/?lang=

  17. Source: eso.org
    Link: https://www.eso.org/public/germany/news/eso8908/?lang=

  18. Source: eso.org
    Link: https://www.eso.org/public/italy/teles-instr/paranal-observatory/vlt/vlt-instr/4lgsf/?lang=

  19. Source: eso.org
    Link: https://www.eso.org/public/italy/news/eso0416/?lang=

  20. Source: eso.org
    Link: https://www.eso.org/public/images/potw1820a/

  21. Source: eso.org
    Title: ES Oblog
    Link: https://www.eso.org/public/italy/blog/climate-change/?lang=

  22. Source: eso.org
    Link: https://www.eso.org/public/italy/news/eso0719/?lang=

  23. Source: aaro.mil
    Link: https://www.aaro.mil/

  24. Source: aaro.mil
    Link: https://www.aaro.mil/UAP-Cases/UAP-Case-Resolution-Reports/

  25. Source: aaro.mil
    Title: Case Resolution of Eglin UAP 2 508
    Link: https://www.aaro.mil/Portals/136/PDFs/case_resolution_reports/Case_Resolution_of_Eglin_UAP_2508.pdf

  26. Source: science.nasa.gov
    Title: uap independent study team final report
    Link: https://science.nasa.gov/wp-content/uploads/2023/09/uap-independent-study-team-final-report.pdf

  27. Source: earthsky.org
    Title: if its not a ufo what is it
    Link: https://earthsky.org/space/if-its-not-a-ufo-what-is-it/

  28. Source: atoptics.co.uk
    Title: At Optics OPOD
    Link: https://atoptics.co.uk/blog/opod-sirius-atmospheric-seeing/

  29. Source: universetoday.com
    Title: Universe Today Sirius, UFO trickster extraordinaire
    Link: https://www.universetoday.com/articles/sirius-ufo-trickster-extraordinaire

  30. Source: public.nrao.edu
    Title: what causes stars to repeatedly disappear and reappear
    Link: https://public.nrao.edu/ask/what-causes-stars-to-repeatedly-disappear-and-reappear/

  31. Source: Wikipedia
    Link: https://en.wikipedia.org/wiki/Twinkling

  32. Source: Wikipedia
    Title: Project Blue Book
    Link: https://en.wikipedia.org/wiki/Project_Blue_Book

  33. Source: universetoday.com
    Title: the mystery of the vanishing star
    Link: https://www.universetoday.com/articles/the-mystery-of-the-vanishing-star

  34. Source: archives.gov
    Title: Project BLUE BOOK
    Link: https://www.archives.gov/research/military/air-force/ufos

Additional References

  1. Source: war.gov
    Link: https://www.war.gov/medialink/ufo/release_1/255_413270_ufo%27s_and_defense_what_should_we_prepare_for.pdf

  2. Source: facebook.com
    Link: https://www.facebook.com/Abovethenormnews/videos/-a-star-was-nearly-erased-from-view-a-distant-sun-like-star-faded-to-a-fraction-/1453590676348966/

  3. Source: instagram.com
    Link: https://www.instagram.com/p/DXsIuypDzPm/

  4. Source: aliensarerunningoperations.com
    Link: https://www.aliensarerunningoperations.com/

  5. Source: aavso.org
    Link: https://www.aavso.org/sites/default/files/publications_files/ccd_photometry_guide/CCDPhotometryGuide.pdf

  6. Source: facebook.com
    Link: https://www.facebook.com/groups/zwoasiusers/posts/945897269102655/

  7. Source: philarchive.org
    Link: https://philarchive.org/archive/GONAPN

  8. Source: facebook.com
    Link: https://www.facebook.com/groups/81273219287/posts/10161742531809288/

  9. Source: milkywayforecast.com
    Link: https://milkywayforecast.com/guides/cloud-cover-stargazing

  10. Source: facebook.com
    Link: https://www.facebook.com/ESOAstronomy/posts/reaching-for-the-stars-chilean-astrophotographer-alexis-trigo-captured-the-vlt-u/1348536203985643/

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