Amateur astronomers could be forgiven for seeing double on Jupiter as the famous Great Red Spot closes in on a colourful rival. A second oval feature is running up against its bigger brother, giving stargazers two red spots to view at once through their backyard telescopes.

Jupiter pictured by Simon Kidd showing its two red spots and moon Io

The spectacle comes just weeks after astronomers reported that one of the giant gaseous planet’s prominent dark belts had disappeared.

The smaller feature – dubbed Red Jr and big enough to swallow the Earth – used to be white. It formed from three oval storms in Jupiter’s atmosphere. Two merged in 1998 and the third was absorbed in 2000 to form a spot labelled Oval BA.

Alert observers noticed that its centre starting to turn red back in 2005 and it became more prominent the following year as it had a previous close encounter with the Great Red Spot. For most of the time, because different bands in Jupiter’s atmosphere rotate at different speeds, the two spots are widely separated. However, they come close together every two years or so, and this has created the present spectacle.

The pair of spots are clearly shown in the accompanying photograph by planetary observer Simon Kidd, of Welwyn, England, taken through his Celestron C14 at his home observatory.

Simon told Skymania: “The two spots are coming quite close to each other so it will be fascinating to watch and see what will happen. Perhaps the smaller spot will fade and lose colour or be deflected by the larger spot. One of the appealing things about astronomy is that one can observe such incredible phenomena from one’s own back garden!”

Robin Scagell, vice-president of the UK’s Society for Popular Astronomy, commented: “This shows that amateur observers can still play a part in monitoring the planets, even from the UK’s cloudy skies. Amateurs around the world can give virtually 24-hour coverage of Jupiter, but the Hubble Space Telescope only observes it occasionally.”

Jupiter is perfectly placed for observing the double act at the moment, rising late in the evening when it appears the brightest object in the sky apart from the Moon. Because Jupiter rotates in a little under ten hours, the spots are visible to us for around five hours at a time. You can find the optimum times, when the Great Red Spot lies on the planet’s central meridian, at this Sky & Telescope page.

Both red spots are swirling superstorms within which winds blow at around 350mph. The Great Red Spot, which is twice the Earth’s size, has been raging since at least 1831 and an earlier form of it was recorded by Cassini in 1665. Infrared images taken with NASA/ESA’s Hubble Space Telescope indicate that Jupiter’s storms are driven by heat from within the planet.

In May, astronomers were surprised when Jupiter’s South Equatorial Belt, which borders the Great Red Spot and is normally one of two main dark belts on the planet, had completely faded away. Amateur astronomers have also been first to detect impact scars on Jupiter.

• Discover space for yourself and do fun science with a telescope. Here is Skymania’s advice on how to choose a telescope. We also have a guide to the different types of telescope available. Check out our monthly sky guide too!