The sky offers many natural and man-made surprises . On any clear night you can see much more than stars . (or even during the day). If you have seen something that has surprised you, consult this guide to try to identify it , before giving up and classifying it as a UFO (Unidentified Flying Object), which simply means that we have not been able to say what it is.
In these paragraphs, the word “object” designates what we have been able to see in the sky.
Is the object really “in the sky”?
Remember that our eyes are not able to perceive distances or heights in the sky , so it is very difficult to see if the object is flying high or low. In fact, on any starry night, we see planets that are a few million km away as well as stars that are 10, 100, or 1000 light years away. Our sight does not distinguish it, since it lacks references. (It is also not distinguished in principle by binoculars or telescope, unless certain techniques are used).
Thus, an airplane that flies only a few thousand meters, can appear like an artificial satellite hundreds of km high. And a smaller and closer object can have the same appearance as a larger and more distant object .
Let us also think that, although on the surface it seems that there is no wind , it can be higher in the atmosphere. Because of this, a small object (made of plastic, paper, etc.) blown by the wind a few dozen meters high, and illuminated by the surrounding lighting or light pollution , can offer the same appearance that a larger object would have in I fly much higher. That is, not everything that has the sky as a “backdrop” is actually “in the sky.”
The movement can give us clues. As a general rule of thumb, the faster it appears to be moving, the closer the object is likely to be to us. Something that seems to move very quickly can never be too far away. Consider a car that passes us quickly, compared to a car that we follow with our eyes for a long time as it travels a road in the distance.
Is the object actually moving?
Our sight is designed for day and ground vision , so night and sky vision is an unfamiliar experience. And perception in unusual situations does not work the same as perception in everyday situations.
That is why we must make sure if the object we see is really moving , especially if we see it in a sky with clouds and clearings . By optical and perceptual effect, lacking references in the sky, it is common to perceive that “a star is moving” when in reality what is moving are the clouds. If it seems to us that “all the lights are moving at the same time”, it is most likely that what is moving is our reference point.
Nor is it useful to take a nearby object as a reference: a tree, a pole, the wall of a building, etc. since any small movement that we make (or the muscles of our head, eyes, etc.) with respect to the reference point would distort the observation and produce a false illusion of movement of the object. We must therefore take as a reference other stars, or a fixed and distant point on the horizon.
The mechanisms by which we perceive reality are very complex. Sometimes we think of our eye as like a video camera, but perception consists of a complicated interaction between the sensory organs and the brain. That is why there are so-called optical illusions , of which many and very funny can be found on the internet, which teach us a lot about how our perception works.
After verifying what is indicated in the previous paragraphs, you can check if the object you have seen fits any of these descriptions.
“Star” that (almost) does not move but is brighter than usual.
It is probably the planet Venus , visible at twilight (sunrise or sunset), sometimes even in the blue sky, in broad daylight, in the morning or in the afternoon. Venus always surprises with its brilliance . It is the brightest object in the sky after the Sun and the Moon.
It could also be the planets Jupiter , Saturn or Mars , which do not shine as brightly as Venus but normally more than the stars. Sometimes Mercury is also visible in the twilight sky.
Some bright stars like Sirius can also draw our attention, since due to the refraction of its light in our atmosphere, it can appear with iridescence of colors.
If it is a planet or a star, we will see it, as the hours go by, move little by little from East to West (like the Sun and all the stars) due to the rotation of the Earth . Perhaps in half an hour this movement can already be appreciated, if reference points are taken on the ground.
None of the planets appear on the star maps or planispheres, since over time (weeks, months) they move in their orbit and thus change their position with respect to the background constellations. To find out which star it is, you can consult a sky guide for the current year, use “planetary type” software, and so on. to know what the sky looks like at a certain time and place.
Slowly moving “star” (faint or bright).
Once we have made sure that the object is actually moving (as indicated at the beginning of this guide), most often it is an artificial satellite (communications, weather, etc) . Many can be seen on any clear night, since the Earth is surrounded by them. Most orbit at heights of a few hundred km. The light with which we see them is reflected from the Sun (because although for us on earth it is already night, “up there” the Sun still shines). That is why they sometimes ” disappear ” when they get into the shadow of the Earth and the Sun no longer gives them.
It differs from an airplane in that we see it move slower, the farther away it is, and it has no flashing lights. With binoculars we will not see on the satellite anything more than a point, due to the distance at which it is (unlike the plane that can be seen larger or with its lights more separated).
Nor should it be confused with a shooting star , as it only lasts for a few moments.
If it is also bright enough ( brighter than most stars), it is probably the International Space Station (ISS) , a manned mission that permanently orbits the Earth at an altitude of 400 km. This “bright spot” will cross the entire sky in three to four minutes . Its light is also reflected from the Sun.
Years ago the Russian station MIR was easily visible in the same way .
The ISS circles the Earth about 15 times each day and is seen frequently after dark or before sunrise, so it’s easy to see it if we know when and where. On the Heavens-Above website(link is external) you can find out when it is visible from your place. Let us point out that it does not carry any propulsion; it just orbits, like the Moon around Earth (albeit much closer).
A row of bright dots that move at the same time, as if it were a “train”.
They see each other often lately. They are the artificial Starlink satellites, launched by the aerospace company Space X, and destined to bring internet coverage to the entire world. There is abundant information about them in the press, for example here(link is external).
Object in movement, very fast, like a trace in the sky that later disappears.
It is a meteor or shooting star : a small particle of material, a few millimeters in size, that travels through space and when it encounters the Earth’s atmosphere, it burns due to friction and produces a luminous trace. There are nights in the year when more shooting stars are seen (for example the Perseids, August 11-13 and other meteor showers), but on any clear night if we observe for a while it is also likely that we will see some.
Its appearance is very varied. They can shine a lot or a little. Its trajectory can be short or long. Some may leave a trail that persists for a few moments and others may not. They are usually quite fast (they disappear before we have time to say it!) But there are also slow ones, which can last several seconds. Sometimes they can show some color .
Large shooting stars are called bolides (they correspond to a “stone” perhaps a few centimeters long) and can be spectacular in their brightness and wake. Some can fragment during their trajectory, present flashes or small explosions, make noise or leave a trail of smoke. Sometimes they can be bright enough to be seen behind the clouds, and then we will see the clouds light up for a few moments. They can also be visible even during the day.
If any fragment falls to the ground, it is called a meteorite . Tons of microscopic and larger meteorites fall to Earth every day, although it is very difficult to find one.
And couldn’t it be a comet?
An object that passes quickly before our eyes is not a comet . These, when they get close enough to Earth, are seen for weeks or months , and in one day they do not move appreciably with respect to the background stars. Along with these, we see them rise in the East and set in the West every night, due to the rotation of the Earth.
Of course, the comet travels at high speed through space, but being millions of km from us, this movement is only appreciated throughout the days.
Every year it is common to see several comets, with telescopes or binoculars , and sometimes with the naked eye as a faint “fuzzy star”. Rarely does any one come within “only” a few tens of millions of km from Earth, and then show us its spectacular tail for days or weeks.
Of course, the particles of material that the comet leaves in its path, when meeting the Earth, become shooting stars or meteors.
Object that blinks or changes the direction of its movement.
Most of us have seen an airplane during the day, but we may not be so familiar with how it looks at night . Jet streams are rarely seen in the dark, so we will identify them as a slow-moving object, with flashing lights, and it may change the direction of its motion when changing course. Some binoculars will get us out of doubt , because we will see it larger or at least with the lights further apart.
Object that increases or decreases in brightness for a while, but does not (or barely) move.
It can be a plane coming from the front (or going away), right in the direction of our vision . In this way we will not perceive its movement, although we will see it increase in brightness (if it approaches) or decrease (if it moves away).
It can also “start moving” at any given time if you change course .
Sudden flash that lasts a few seconds and fades.
There are several possibilities:
- It can be a meteor or shooting star that comes right in front, so we do not see the length of its stroke but only a flash.
- It can also be (and will be the most frequent) an artificial satellite of the “Iridium” type (see previous section), which have solar panels that reflect light, so that when the panels point towards the observer, as if it were a mirror, we see a flash that lasts a few moments. At that time its brightness may be higher than that of any star or planet that we see . As the artifact rotates, after a moment the panels will no longer point towards us, thus the satellite will no longer be visible because it does not reflect light.
On the Heavens-Above website(link is external)you can find out when an “Iridium” is visible from your place. Almost every night one can be seen.
During the day, a luminous spot almost like “another Sun”.
It is a parhelion , a curious phenomenon caused by the refraction of the sun’s rays . We have a specific article on this phenomenon in which there are photographs taken by ourselves.
Large, round, shiny object that moves in different directions.
There are different objects of this type that are not astronomical phenomena, but rather atmospheric . Electricity from storms can form ionized air masses called sparkles or round rays. They are usually spherical but also sometimes cylindrical or ovoid-shaped, very bright and with different colors. Due to their electrical charge, they move almost as if they were animated beings , changing direction and speed, either through the air or on the ground.
Also the electricity from the high voltage cables can give rise to a similar effect, producing balls or disks of ionized air in motion, called crowns .
Objects of other characteristics.
These are other phenomena to consider:
- The Sun or Moonthat when rising or setting can adopt flattened shapes (discs) or vertical (pillars) caused by atmospheric refraction and reflection, not being easily identified; Duplicate, oval, halved, etc. shapes can also appear. red, orange or yellow colors.
- We can witness the green ray(the last ray of the setting Sun is green. It is seen with relative frequency on the sea horizon and very clear sky).
- The bright planetslike Jupiter or Venus can also be refracted and reflected when they are flush with the horizon.
- Halos, crowns, arches, rainbow fragments and other luminous phenomena of solar refraction,similar to parhelios.
- Noctilucent clouds, located high in the stratosphere, that at night reflect the light of the Sun when it is below the horizon.
- NorthernLights / Austral showing colored shapes that move in the sky as a result of solar activity.
- Miragesdue to the refraction or reflection of images in hot and cold atmospheric layers.
- Wispscaused by the release of methane gas into swamps or marshes.
- Common” fires of San Telmo” in the sea by ionization of the air (also visible on land or from airplanes).
- You make light of cities, cars, a lighthouse, luminous projectors for parties, etc. located at a certain distance, not directly visible, but whose light reaches us reflected or refracted in the clouds and the atmosphere.
- Incredible as it may seem, birdslit from below by light pollution can offer surprising aspects. Remember that our eyes do not distinguish at what height or distance the object flies.
- Luminous beaconsfor air traffic on the top of a mountain (or also antenna lights, etc), because in the dark you cannot see the mountain and the beacon appears to be suspended in the air.
- Meteorological rocketsor the glow of the sodium clouds ejected by them.
- Other devices suchas balloon-sounders or radiosondes, aerial targets for radar, etc.
Objects observed in photography or video:
If the object was not observed directly but is a photograph or video, then many more factors come into play : light, distance , movement of the camera or the object, openness , sensitivity of the film / chip, lens used, etc. . Astronomical photography requires special techniques to get it right. If we simply take a freehand photo with our pocket camera, what we will get will not look much like reality.
First thing: the camera must be firmly seated on a tripod or support. If not, the movement of the pulse will make it impossible to clearly distinguish the object in the image. In addition, it is necessary to take into account the reflections or refractions in the optical elements (lenses, mirrors, diaphragms), diffraction effects , focus distance and depth of field . For example, images out of focus(which frequently happens in cameras with “zoom”) they adopt different forms that do not have to do with the real shape of the object observed, but rather with the shape of the optical elements: lenses, mirrors, diaphragms, etc. of the camera or instruments used.
On the other hand, it is necessary to consider the possible defects (scratches, stains, particles …) in the lens or in the optical elements, or also in the negative / chip. Likewise, it is necessary to take into account possible failures in the development / processing of the images, and to know how this process has been done. For example, in digital photography, it is common for “hot pixels” to appear ; and in astronomical photography, especially long exposure photography, cosmic rays can be detected (charged particles from space that arrive continuously; they are harmless) that when hitting the chip will manifest as small dots in the image.
For all this, the most desirable thing would be to have more than one image of the object, if possible obtained with different cameras.
Consider also the following comments:
- It must be borne in mind that the shadow of the Earth is cone-shaped, therefore, although for the observer on the ground it is night, for an artificial object in the upper atmosphere it can be daytime , so the object can reflect light and shine.
- Various astronomical objects or not, seen in unusual circumstances, can surprise us (light sources located behind the horizon, etc).
- Of course, as long as the observation is made through a glass, window, etc. It will be necessary to consider the possible reflections in it, coming from light sources located behind the observer.
- On the other hand, “second-hand” testimonies should not be taken, but narrated directlyby the person who observed them, since the transmission may inadvertently distort the information. It is also much better that the testimonies are recent, since our memory is plastic and changes over time, it is not like a camera.
