Observations and Sketches of the Shrinking of GRS
Posted 11 March 2013 - 11:21 AM
Since I posted this yesterday I changed my web page so all of the sketches can be seen simply by scrolling up and down. This makes it easier to compare how the GRS has changed over time:
I was watching a TV program recently about Jupiter and it mentioned that Jupiter's Great Red Spot (GRS) is shrinking in length. I had heard this before but it got me wondering if I had seen and recorded this phenomena during my telescopic observations of the planet since 1973.
In looking back at one of my earliest observations and sketches of Jupiter in 1973 with a 60mm refractor the GRS looked elongated to me:
The same held true with Jupiter in 1974 when I was using a 4.25" reflector:
The GRS had faded to a dim gray color in 1976 but the Red Spot Hollow was noticeably elongated when I observed it with a 6" reflector in early 1977:
During my observations of Jupiter in the 1980's the GRS had a more oval shape to it:
My more recent sketches of Jupiter show the same thing:
So it seems likely I was recording the decreasing length of the GRS from 1973 until today. This is because leaving aside differences in the telescopes and magnifications employed over the years they all show the same trend in the data.
To verify this I went I went to the Sky and Telescope website and came across a couple of articles that discussed how the GRS has been shrinking in length since the late 1800's. In the late 1800's it was almost 35 degrees wide. However by the time Voyager 1 and 2 visited Jupiter in 1979 it had shrank to 21 degrees. The height of the GRS has remained approximately the same.
It confirmed also that between 1975 and 2010 the GRS has been shrinking in length from around 24 degrees to around 15 degrees. So my observations were accurate.
It was a good thing I made sketches over the years as without them I may not have realized how much the GRS has changed over time if I had just taken notes.
Posted 11 March 2013 - 12:44 PM
another reason to look at my favorite planet
Posted 11 March 2013 - 04:24 PM
Posted 12 March 2013 - 07:21 AM
Posted 12 March 2013 - 09:12 AM
Yes given the overall trend over time it seems like a good idea to observe the GRS when time permits.
Posted 12 March 2013 - 03:29 PM
Great collection of Jupiter sketches. Your sketches span a lot of time and I'm sure you've noticed many changes on Jupiter along with the shrinking GRS. I remember when the GRS was a deep red as you depicted in your early sketches. My first good views of Jupiter were thru a Criterion RV-6.
Thanks for posting. Dean
Posted 20 March 2013 - 02:46 PM
Thanks, it looks like you have owned some fine scopes over the years including the Cave 10" and the RV-6.
Posted 13 April 2013 - 12:21 PM
I recently came across a sketch of Jupiter and the GRS made by Étienne Léopold Trouvelot of Jupiter on November 1, 1880 using the U.S. Naval Observatory 26" refractor:
I noticed that even accounting the larger aperture he was using compared to mine the length GRS back then was significantly longer than what I recorded: