Not-So-Great Red Spot of Jupiter

Be quick to observe the “Not So Great Red Spot of Jupiter” before it becomes even smaller or may even disappear!

A favourite telescope object for Malaysian astronomy enthusiasts is the largest planet Jupiter with its many swirling clouds making bands of white, red, orange, brown and yellow colours. I could remember first observing Jupiter and its Great Red Spot during the 1980’s in Universiti Sains Malaysia in Penang, Malaysia. Comparing the size of the Great Red Spot at that time with its size at the present time, I can clearly make out that the size has decreased even by visual observation through the telescope. The picture above shows the size of the spot as observed in 1890 (2.8 Earths size) with that of 2015 (1.2 Earths size)! Perhaps during our stargazing sessions in Penang we should announce to the stargazers “Come and see the Not So Great Red Spot of Jupiter” or just the “Red Spot of Jupiter”.

The questions that come to many people’s minds are “How fast is the spot shrinking now?”, “Will the spot disappear?” and “What makes the spot shrink?”. To get some answers to these questions, we have to take a basic lesson about the previously called “Great Red Spot of Jupiter”.

The Great Red Spot is a vast and persistent anticyclonic storm on Jupiter located at 22 degrees south of the equator, it produces wind speeds of up to 432 km per hour. Comparing with a cyclone on Earth which has a low pressure central area and a higher pressure outside the central area, an anticyclone is just the opposite with a higher pressure central area and a low pressure outside the central area. The anticlockwise rotation of the Great Red Spot is due to the large Coriolis forces acting on the atmospheric particles caused by the fast 9 hour and 56 minute rotation period for Jupiter, which is a much faster rotation rate as compared to that for the Earth.

The first telescopic observations of a large red spot Jupiter on were made from 1665 to 1713. The first confirmed sighting of the Great Red Spot was in 1831. Researchers are not certain whether earlier observers who saw a red spot on Jupiter were looking at the same storm as we see currently.

Measurements made by Hubble Space Telescope from 2009 to 2020 show that the speed of the outer winds of the Great Red Spot had increased by eight per cent while the inner winds are slowing.

A NASA team has discovered that the Great Red Spot is getting taller as it shrinks. Just like the many atmospheric features on Jupiter, the Great Red Spot is constantly changing in size and shape and its winds can shift.

So next time when you observe Jupiter with your telescope, remember to have a good look at the Great Red Spot or perhaps the Not So Great Red Spot and remember to take pictures of the great Jovian storm as souvenirs.  The Great Red Spot is dying and some scientists predict that it could disappear forever in as little as 20 years.

Article by Dr Chong H.Y.
Images by ASP Members Mr. Lim C.K, Mr. Michael Teoh & Mr. William Chin