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Andromeda Galaxy
Image of the Andromeda Galaxy captured at the Alqueva Lake Observatory through the telescopes used in the Astronomical Observation sessions.
The Giant Jupiter!
Jupiter is the largest planet in our solar system, its mass is 2.5 times that of all the other planets. It has an orbital period of 11 years and 10 months and takes about 10 hours to complete one rotation around its axis, compared to Earth which takes 24 hours to complete one rotation.
We are talking about a body with a diameter of 11 Earths that completes a rotation in less than half a day… Incredible!!
Jupiter is a gaseous planet, which leads many to believe that it is possible to travel from one side of the planet to the other without any obstacles. On the contrary, like the other gaseous planets, Jupiter's core is rocky and measures about 20,000 km in diameter, or approximately 1.5 times the size of our planet.
Its atmosphere, composed mainly of hydrogen and helium, is very dynamic and is home to the most well-known storm in the solar system, which has been monitored for over 300 years. This storm, Jupiter's Great Red Spot, is about 16,350 km long or 1.3 times the size of Earth.
Every year, given the movement of the planets around the Sun, there is a day when Jupiter, Earth and the Sun are aligned. This day is called the opposition of Jupiter and marks the day when Earth and Jupiter are at their point of closest approximation, the distance that separates them is just over 588 million kilometres.
The star that never was.... is it really?
Jupiter's high mass sometimes leads to the idea that Jupiter is a "failed star." Despite being quite massive and having a chemical composition very similar to a star, Jupiter is very, very far from having enough mass to initiate hydrogen fusion. For comparison purposes, the star – 2MASS J0523-1403 – is one of the smallest known and has a mass equivalent to 85 Jupiters.
The star EBLM J0555-57Ab, although smaller than Jupiter, has a mass equivalent to 85.2 times that of Jupiter.
Discovery and observations of Jupiter
Júpiter destaca-se fácilmente no céu dado o seu elevado brilho, por causa disto, todas as antigas civilizações possuem algum registo de Júpiter nos seus monumentos ou manuscritos. Para os gregos o astro brilhante no céu representava Zeus, o lider do panteão grego. Para os romanos era “Jove” por vezes denominado “Dyeus-Pater” que mais a frente foneticamente evolui para Júpiter.
Galileo Galilei
On January 7, 1610, Galileo Galilei was the first person on Earth to observe Jupiter through a telescope.
Illustrations made by Galileo of the motion of the Jovian moons around Jupiter in 1610.
Galileo observed that there were four bright points next to Jupiter. Between January 10 and 19, he noticed that these points appeared to be moving around Jupiter. Interestingly, the observation was confirmed by Jesuit astronomers in Rome. Galileo named the bodies “Medician Planets” in honor of the Medici family, his patron saint.
Contemporarily, in honor of Galileo, this system is known as “The Galilean moons” composed of Io, Europa, Ganymede and Callisto.
Callisto, Ganymede, Europa and Io are the moons that make up the Galilean system and are the largest of the 95 moons that orbit the planet. Three of these moons, Ganymede, Callisto and Io, are larger than the Moon and Ganymede is the largest moon in the solar system, larger even than the planet Mercury. These moons are easily observed with binoculars and over the course of 1h30 it is possible to observe the movement of the moons around Jupiter.
The Galilean moons
Ganymede
Image (PIA 00716) of the moon Ganymede captured by the NASA-Galileo Orbiter probe.
Europa
Image (PIA 19048) of the moon Europa captured by the NASA-Galileo Orbiter.des probe
Calisto
Image (PIA 03456) of the moon Callisto captured by the NASA-Galileo Orbiter spacecraft.
Io
Image (PIA 00583) of the moon Io captured by the NASA-Galileo Orbiter spacecraft.
Contrary to what many people may think, all the gas planets in the solar system have ring systems. Jupiter has rings, just like Saturn, but they are not as bright and cannot be seen through telescopes. The rings were discovered by the Voyager 1 probe in 1979.
The rings
Image (PIA 00538) of Jupiter's main ring system captured by NASA's Galileo Orbiter in the 1990s.
Between 1995 and 2004, the NASA Galileo Orbiter probe captured numerous images of the Jovian ring system and discovered that it was formed through the collision of asteroids with some of Jupiter's moons.
It was first recorded by Robert Hooke in May 1664. In 1665 Giovanni Cassini also observed a spot on the planet's surface. The NASA Juno probe launched in 2011 took 5 years to reach Jupiter and there captured the best images of Jupiter's atmosphere that we have today.
The Big Red Spot
Image (PIA 21985) of the Great Red Spot captured by the NASA-Juno probe.
The Great Red Spot is the largest and most persistent storm in the solar system. With winds ranging from 430 to 680 km/h. The origin of this storm is still unknown today.
Image/Time-lapse (PIA 22178) of the Great Red Spot, captured by the NASA-Juno probe.
The gases at the top of the storm are very hot compared to the rest of the planet's surface. According to a paper published in 2016 in the journal Nature, researchers say the source of heat could be acoustic waves, caused by the storm's high turbulence.
This storm is visible through a telescope and its red color contrasts well with the rest of the planet. The storm moves longitudinally through Jupiter's atmosphere and takes about 10 days to complete one orbit around the planet. Given Jupiter's high rotation speed, here on Earth we see the storm every 10 hours.
Jupiter is undoubtedly one of the best objects in the sky to observe through a telescope. If atmospheric conditions allow, we can observe the surface of Jupiter in good detail while also observing the Galilean system around the planet. The better the conditions, the greater the color contrast of Jupiter's clouds. In total, we can see:
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Detail of clouds in Jupiter's atmosphere
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The four Galilean moons
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The Great Red Spot (not always visible)
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A good contrast of colors between the clouds.
From time to time it is possible to observe the moons transiting the planet and, with large aperture telescopes, like the ones we have here at OLA, it is possible to see the shadow of the Galilean moon projected onto the surface of the planet.
Jupiter at the Alqueva Lake Observatory - OLA
Image (PIA 23437) of the shadow of the moon Io cast on the surface of Jupiter. Captured by the NASA-Juno spacecraft.
When is the best time to observe Jupiter?
Jupiter will begin to appear in late September 2024 and will remain visible in the second Astronomical Observation session of the evening until late October. Jupiter will remain in the sky and visible in the Astronomical Observation sessions until late March 2025.
To obtain a good image through a telescope, it is crucial to observe the planet when it is high in the sky. The higher the better and the colder the better.
The best time to observe Jupiter at the Alqueva Lake Observatory in the Astronomical Observation sessions is during the months of December (2024), January (2025) and February (2025). In December and January we recommend the second session of the evening and in February we recommend the first session of the evening.
In 2025, Jupiter, after temporarily disappearing from the night sky at the end of March, will only reappear in the sessions at the end of October.
You can consult our Astronomical Observation page for more information.