Steve’s Virtual Planet

Filters for viewing Jupiter’s GRS

Jupiter has been a lot of fun for me this apparition. It’s been higher in the sky than last time and much easier to see right from my driveway through a very convenient gap in the trees. I’ve been able use one of three scopes at home (3 inch refractor, 5 inch Mak & 6 inch Sch-New) and two scopes at Fernbank Science Center (11 inch SCT and the 36 inch Cassegrain). But despite all that aperture and all that glass, the brightness of the planet has made the Great Red Spot (GRS) difficult to see.

Recently, I asked several of my fellow star gazers about using filters for Jupiter’s GRS. I had tried several suggestions from the Lumicon filter guide and another related article on SciAstro. However, this year the GRS has not been very prominent so even the “standard” selections for these filters wasn’t much help. One of my colleagues suggested using a SkyGlo filter, which I had actually seen a reference to in an article somewhere (just do a Google search on Jupiter Sky Glow Filter). It was a DUH moment but I remembered immediately. So, I would be using that filter on the next opportunity and comparing to the earlier attempt. All the trials below were using a 5 inch Maksutov in my suburban driveway.

GRS viewed with yellow #12 and yellow-green #11 filters is not a big difference. I tried these on Halloween 2010 when the seeing wasn’t all that great anyhow, so perhaps the test was not conclusive.

I’ve seen recommendations for the Blue #80A and Dark Blue #38A in several places, including the link below.  I think my 5 inch Mak is too small to use these effectively since it darkens the image quite a lot. So, I tried these the next time I had a good chance to catch the GRS, on Nov 8, 2010.

Using the Orion Sky Glow filter gets much better results, although on this occasion, it was still quite a challenge. The seeing has not been real good this season here in the big city. So, one has to work really hard to get the desired view. So, I am hoping for perhaps one more chance to get the GRS from my driveway early enough in the evening before the “giant pine tree mask” gets in my way to south!

Here is some more information from someone who should know. Damian Peach gives these recommendations on his web site :

I highly recommend the use of coloured filters for observing Jupiter. These can be easily obtained from many suppliers. For Jupiter the most useful filters for the visual observer are Red and Blue. Smaller scopes (less than 20cm aperture) may prefer Orange or Light Blue. Filters worth considering are Wratten #25 (Red), #21 (Orange), #38A (Dark Blue) and #80A (Light Blue.)

See my Sky View Tip #1 for more on how I tracked the GRS on Halloween, 2010. Check some of my other posts with further tips on using using Sky View Cafe.