This blog entry will tackle one of the most asked questions during our sunset and stargazing tours: what are those objects streaking in the sky we often see above our heads? These days we are very close to the ETA Aquariids meteor shower, so I think it is interesting to dedicate this entry to explaining a bit what they are.
Stars are objects that emit electromagnetic radiation thanks to thermonuclear fusion: for the most part, hydrogen fuses into helium and releases a ton of energy throughout the spectrum, part of which is visible to the naked eye. This is why we see them shine in the night sky. In addition to the visible part of the spectrum, stars also emit radio waves, microwaves, infra red, ultraviolet, X rays and gamma rays but we need special instruments to detect that radiation. They do not appear to move in the sky (truth be told, they are all involved in a cosmic dance but over such long time that we are not able to tell) so, when we look up, we see them in the same position relative to one another. In addition to stars, we are often able to see the closest planets in our solar system such as Venus, Mars, Saturn and Jupiter (depending on the latitude we find ourselves, Mercury could also be visible). Unfortunately, Uranus and Neptune are too far away and faint to be spotted without a telescope. Usually, we can identify them because they are located along the Ecliptic (the orbital plain of all the planets, which from our vantage point coincides with the path the Sun follows during the day), because they do not twinkle and, most importantly, because over the course of days and weeks they move relative to the stars in the background. However, over the course of the same night, they appear to stay in the same place.
Of course, there are plenty more celestial objects that we can see when we are stargazing, and some of them are changing their position rapidly: if they move in a straight line slowly and steadily, most likely they are satellites (lately we have to thank Elon Musk for putting up tens of thousands of them as part of his Starlink megaconstellation!). We also often see the International Space Station (easily identified because it is as bright as Jupiter but it moves), the Tiangong Chinese Space Station and the venerable Hubble telescope. If you want to see when they pass above us there are several websites and apps tracking them.
Sometimes, however, we see bright objects zipping across the sky and disappearing very quickly: those are shooting stars, the ones we like to wish upon especially around August 10th or 12th. But what are they exactly? Are they stars falling?
Well, sorry to burst your bubble, but the answer is no, they are not stars and they are not falling onto Earth. The technical term doesn’t sound as catchy as shooting star because what they are is ‘interplanetary debris’ encroaching Earth’s orbit. A more familiar name is meteors. Scattered within the Solar System there is a lot of dust, bits of ice and rocks floating around: sometimes, these objects are caught by the gravity of our planet and start moving towards us. When they enter the atmosphere, usually they burn up leaving a trail of light and gases that we call shooting stars. As they careen through the atmosphere, because the air is made of increasingly denser particles, these so-called meteoroids compress the air in front of them (therefore increasing their temperature) making them glow. When the air reaches roughly 2000º C the material making up the meteoroid vaporizes leaving the trail we are all familiar with.
Although most shooting stars look white to the naked eye, when photographed with sensitive cameras they appear to glow in many different colors depending on their chemical composition: they can appear reddish, greenish or purplish.
Thankfully for us, most meteors are tiny in size (I am talking millimeters) and completely vaporize in the atmosphere, but some are bigger and when they burn up, they burn up bright! those are called fireballs and I have seen a few even during daytime.
When a meteoroid is really big (one meter in diameter and more), things can get serious: as a matter of fact, when they go through the atmosphere they break apart and crumble and actually reach the Earth’s surface. Those we call meteorites and they take up weird shapes due to the extreme heat they went through until touchdown.
Meteorites are extremely interesting for scientists because they allow them to study remote bodies without having to build and send spaceships and probes, as they fall right on our lap.
Meteorites are often seen as one-offs, rare occurrences on apparently random nights. However, there are predictable times of the year when we are able to see many shooting stars within a short span, usually days or hours, and those are called meteor showers. The most famous one is the Perseid meteor shower (in Spanish they are called Lagrimas de San Lorenzo, St. Lawrence’s tears) around August 12th.
Meteor showers are different from meteorites because they come from debris left by comets: when our planet orbits the Sun, it encroaches the path of said comets and the cloud of debris creates this magnificent show where we are able to see tens of shooting stars in a few hours.
Keep your eyes open and your wishes ready because we are approaching the ETA Aquariids meteor shower, which will peak between May 5th and 6th and is the result of our planet crossing the path of the famous Halley’s comet. Join us for an unforgettable stargazing tour or, if you are not in Tenerife, go to a dark sky location, bundle up and look towards Aquarius in the pre-dawn hours to experience this incredible show!
Written by Dani
