Below are phenomena that involve some lights or "fires" visible in the sky. Here are some of the most spectacular sightings that an amateur can witness: comets, meteor showers and bolides; but other sightings also fit into this category, this time due to human space exploration; there are countless objects orbiting the Earth that humans have put there, and sometimes we are lucky enough to observe them.
[accordion title=»I. Meteors»]
Meteors are dust particles in space (as small as a grain of sand or rice), which when crossing Earth's orbit, are intercepted and impact our atmosphere, burning completely as they pass through it. This process takes only a few seconds, but is usually bright enough to produce a flash visible from Earth. This makes for nice views of meteors streaking across the night sky, sometimes with long trails. On a typical clear night, around 5 meteors can be seen per hour. These dust particles mostly come from the remains of comets, which when passing near the Sun release a large amount of material in the form of meteoroids (dust particles). Meteors are often mistakenly called shooting stars, and a subclassification of them is meteor showers.
[/accordion] [accordion title=»II. Meteor showers»]
It is a phenomenon in which, during certain days of the year, the number of meteors visible in one night increases considerably. They occur because the Earth in its orbit passes through an area with abundant dust particles, which have been scattered in the form of a trail by some comet; while our planet passes through this area, it is possible to see between 20, 50, even more than 100 meteors per hour (in meteor storms even thousands can be seen per hour). The meteors seem to "come" from a particular region of the sky (the area where the particles are scattered); this region is called radiant, and to help orientate their location, showers are named according to the constellation in which the radiant is located (e.g. if it is in the constellation of Leo it is the Leonid shower; in the constellation of Perseus, the Perseids, etc.). The activity of a shower is "calibrated" by a standard measurement, called Zenital Hourly Rate (THZ) (number of meteors visible by an observer, in 1 hour, with ideal conditions and the radiant at the zenith).
[/accordion] [accordion title=»III. Comets»]
They are widely known celestial bodies, due to their particular configuration: a bright body provided with a "line" either "hair", which can be as long as 1 AU (distance from the Earth to the Sun). Comets are of great importance because they are composed of a wide range of rocky and organic material: some are essential for the appearance of life. These elements are arranged as an icy "crust" on their surface, which does not have a visible tail until it gets close enough to the Sun; at that time, radiation and solar wind cause the comet to release many tons of material in the form of dust and gas, forming the "tail"; this always points away from the Sun, because the tail is simply the material ejected or "pushed" by the solar wind. Comets usually have very long and elliptical orbits, making them return and become visible again every few years.
[/accordion] [accordion title=»IV. Meteorites »]
They are small objects that, unlike a meteor, do not completely disintegrate when they pass through the Earth's atmosphere, so they reach the surface forming a crater. They are less than 50 m in size, although it can be said that "large" meteorites are much rarer than small ones (only a few centimetres); meteorites are much less frequent than meteors, due to the action of the atmosphere which destroys most meteoroid particles in a few seconds. This category also includes fireballs, described as "fireballs".fireballs» with a large trail, which are visible for several seconds or minutes, and are usually accompanied by a loud bang/explosion, which destroys part of the meteor, while some fragments reach the surface and become meteorites, although without leaving a crater mark.
[/accordion] [accordion title=»V. Artificial satellites»]
An artificial satellite, in the case of our planet, is any object placed in orbit around the Earth by human beings. This category includes satellites themselves (communications, military, scientific, climate, etc.), as well as other objects, such as International Space Station, the space shuttle or the Hubble space telescope. On a dark, clear night, an artificial satellite can be seen with the naked eye as a faint point that moves faster than the apparent movement of the stars; in fact, an artificial satellite can cover the entire celestial vault in ~5 minutes, and they are easily distinguishable compared to the stars. Objects like the Space Station or the space shuttle are much easier to observe, as long as they pass through the coordinates where you are.
[/accordion] [accordion title=»VI. Iridium flare»]
Iridium is a type of communications satellite (66 in total) from the Motorola company put into orbit to provide mobile satellite communications; The main purpose of these satellites went bankrupt and they currently have military applications, but here they have a separate mention because, due to the configuration of their antennas, the Iridium satellites reflect the light of the Sun in a very powerful way, producing flashes that can reach Earth. between magnitude -4 to -7, which is highly bright (the magnitude of the planet Venus is -4). These brief but strong flashes are called Iridium flares. In addition to being curious to observe them (for which you can find out if any will transit our area), these satellites are frequently confused with UFOs.
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