Jupiter’s surface hosts innumerable storms at all times. The most famous storm of them all is the Great Red Spot (GRS) that has been churning in the gas giant’s atmosphere for the past three centuries, if not more.
In this guide to seeing Jupiter’s Great Red Spot with a telescope, we will explore what this incessant storm is all about. We will also review the recent news that this storm might be disintegrating and shrinking.
Will it really disappear, just like that? Chances are that it won’t, read on to find out why.
Finally, this guide will provide you the knowledge needed to observe the Great Red Spot. You’ll be pleased to learn how easy it is to see with a decent telescope from your own backyard.
What is the Great Red Spot?
The Great Red Spot is a high-pressure region in Jupiter’s southern hemisphere that has existed for more than three centuries. It rotates every six Earth days.
Rotating in an anticlockwise direction, the Great Red Spot is neatly sandwiched between cloud layers moving in opposite directions.
To its north, a layer moves eastward while to its south, another layer moves west. This resulted in its nature of being counterintuitively calm at the center while wind speeds at its boundary range up to 425 miles per hour.
While the origin of the storm’s brick-red color is unknown, scientists believe that ammonia, sulfur, and phosphorus in Jupiter’s atmosphere play a major role.
How Big is the GRS?
The storm is oval in shape and ranges over 7,500 miles (12,000 km) from top to bottom. Unlike Earth, there is no surface on Jupiter to break the storm, which is why its size has remained constant across centuries.
Is Jupiter’s Great Red Spot Shrinking?
Since the 1920s, Jupiter’s Great Red Spot has been shrinking. It is currently half the size of what it used to be when it was first discovered three centuries ago. See more on that in the video below.
In addition to its decreasing size, the storm has gotten redder as well.
In 2019, amateur astronomers noticed bands of red clouds flowing out of the storm. This was unusual because storms as huge as the GRS grow in size by gobbling up smaller storms.
While this gave the illusion that the Great Red Spot was disintegrating, scientists believe that it is normal dynamics on the turbulent Jupiter. Gas flowing in and out is part of how a storm behaves.
Despite all these changes, the fact that Jupiter’s underlying vortex remains unchanged indicates that the storm is not going away anytime soon.
(A vortex is a place where two jet streams flowing in opposite directions collided to create the GRS. The same vortex now drives the Great Red Spot.)
As long as its vortex is stable, the GRS might continue to shrink (but not disappear), or it may swell up to its original size in the next few years.
How to Observe the Great Red Spot With a Telescope
Jupiter’s Great Red Spot is seen roughly twice per day and is best viewed when the storm crosses Jupiter’s meridian (the centerline of the planet). Better yet, if you can see it when Jupiter is at or near opposition, it will appear larger than at other times because the planet is much closer to us.
Oppositions happen every thirteen months. Look out for them in July 2020, August 2021, and September 2022. Jupiter presents a spectacular telescope site for a few weeks either side of the opposition dates themselves.
When is the GRS Visible?
Jupiter’s Great Red Spot is visible roughly twice a day.
From Jupiter’s pictures, you might have noticed that it is not perfectly spherical, but more like a slightly squashed ball. Due to its gaseous nature, Jupiter’s equator rotates faster than its poles.
As a result, the Great Red Spot that resides near this equator rotates around the planet every 09h 56m and is visible from Earth at least two times on any day.
With every rotation, the storm crosses an imaginary line called meridian that is directly facing us and connects Jupiter’s north and south poles.
This moment is called a transit, and transits are the most opportune times to observe the Great Red Spot. The storm is visible for an hour before and after the transit time, giving you plenty of time to observe (weather permitting).
We’ve provided the storm’s transit times for July 2020 (an opposition month) to show how regularly the GRS is visible.
You can see that there are many opportunities to observe it during the hours of darkness, at least 25 by our count, and that is a typical pattern.
You can find the complete list of transits for when you plan to observe using Sky & Telescope’s applet.
|Date||Time (UT)||Date||Time (UT)|
|01 July 2020||01:55, 11:50, 21:46||17 July 2020||05:03, 14:58|
|02 July 2020||07:41, 17:37||18 July 2020||00:54, 10:49, 20:45|
|03 July 2020||03:33, 13:28, 23:24||19 July 2020||06:40, 16:36|
|04 July 2020||09:19, 19:15||20 July 2020||02:32, 12:27, 22:23|
|05 July 2020||05:10, 15:06||21 July 2020||08:18, 18:14|
|06 July 2020||01:02, 10:57, 20:53||22 July 2020||04:10, 14:05|
|07 July 2020||06:48, 16:44||23 July 2020||00:01, 09:56, 19:52|
|08 July 2020||02:40, 12:35, 22:31||24 July 2020||05:48, 15:43|
|09 July 2020||08:26, 18:22||25 July 2020||01:39, 11:34, 21:30|
|10 July 2020||04:18, 04:13||26 July 2020||07:26, 17:21|
|11 July 2020||00:09, 10:04, 20:00||27 July 2020||03:17, 13:12, 23:08|
|12 July 2020||05:55, 15:51||28 July 2020||09:04, 18:59|
|13 July 2020||01:47, 11:42, 21:38||29 July 2020||04:55, 14:51|
|14 July 2020||07:33, 17:29||30 July 2020||00:46, 10:42, 20:37|
|15 July 2020||03:25, 13:20, 23:16||31 July 2020||06:33, 16:29, 02:24|
|16 July 2020||09:11, 19:07||01 Aug 2020||02:24, 12:20, 22:16|
What Size Telescope Do I Need To See It?
A 4” to 6” scope is adequate to spot Jupiter’s Great Red Spot.
Scopes with larger apertures will give you sharper and more distinct views, as the video below demonstrates with a 6″ telescope.
As with observing any celestial body, the right conditions are important.
Wait for Jupiter to be a high up in the sky so that you don’t have to tussle with thicker layers of turbulent air near the horizon. Observing under dark skies is always a plus.
Also, make sure to cool your scope to ambient temperatures before you begin observing. Again, this reduces turbulent airflows.
How Can I Make the GRS Easier to See?
You can enhance the contrast of the Great Red Spot using a light green or dark blue filter. See our article on telescope filters (opens in a new tab) for the best filter numbers to use.
Telescope filters remove certain colors from your view, thus enhancing the feature you are observing. A general rule is to use a filter that is the opposite color of your object.
For Jupiter’s Great Red Spot, a light green or blue filter will work well.
A light green filter will intensify the storm’s reddish color whereas a blue filter will enhance the boundaries between belts and zones. This way, the GRS will appear much darker when compared to its surroundings, making it easier to see.
Similar to observing any celestial body, Jupiter’s Great Red Spot will take time, patience, and effort.
Since the gas giant is so far away from us, its features need to be seen using a telescope with at least a 4” aperture.
Light green and dark blue filters work best to enhance the Great Red Spot’s color, making it easier to identify.
Dark skies, Jupiter’s position in the sky, the Great Red Spot’s position on the surface of Jupiter, and good telescope collimation are the other key things to consider when you’re looking at the Great Red Spot with a telescope.
The sight that will greet you at the end of this hard work will be more than worth it!