May 7, 2018: Stunning Io Transit! And Planetary Disappointment with the SCT

In my first time out with the scope since Moab in March (lame, yes I know), I got my first observing session with Jupiter for the season at 2am late Saturday night (technically, Sunday morning).  I could have gone out within the past month or so and caught Jupiter earlier, but I just didn’t have the astronomical motivation to get out.  Now that Jupiter is rising around 8pm or so, and getting high enough in the sky just before midnight (above 30 degrees by 11:30ish), it was time to stop procrastinating.

Well, it wasn’t all procrastination.  The weather has been pretty bad of late here – lots of snow and clouds in April along with some supremely high winds – sustained gusts of 50 mph, and I’m not exaggerating one little bit.  There’s also been quite a lot of rain so far in May.  But it was finally clear, and it was time to get out there already!  Especially since Jupiter is pretty much at opposition and is as big as it ever gets.  Jupiter’s size doesn’t vary as much as Mars does over the course of a year, but it still varies.  The smallest it ever gets is about 31 arc seconds, and the largest is about 45.

I just wanted to have a quick peek at the Io shadow transit with the Mak on my balcony.  After some initial problems with the NexStar handset – the wiring is loose by the telephone jack clip that plugs into the scope, and I was getting weird error messages – I finally got underway.

I was a bit nervous going out, because someone had fired off 9 shots in succession somewhere very close by in my neighborhood just the very night before.  I immediately called 911, and half a dozen police cars swarmed right by my condo and took down and arrested three people just 50 feet from the very balcony I observe from.  And as one of them was being put into the back of the patrol car, I heard one of the officers say that he had a gun.  Gulp!

My astronomical fervor overrode my nerves.   The seeing was RIDICULOUSLY GOOD.  Absolutely zero wind; perfectly steady.  I went straight to 246x with the Mak without a problem.  Four bands on Jupiter were plainly visible, and more than just being visible, you could easily see that there were some differences in their banding, their widths, both horizontally across the face of Jupiter and vertically as well.  Probably about the best seeing I’ve had out here since moving out west from Manhattan a couple of years ago.

Even better, not only could I plainly see the tiny dot of a shadow moving along on Jupiter’s face, but I could also still see Io itself too!  I had never seen Io before while it was on the face of Jupiter in its previous crossings.  Normally, there is a good bit of lag time between when the moon itself transits and when the shadow begins its journey, so that the moon and its shadow are pretty well separated.

This is the normal state of things, with the moon and the shadow having quite a bit of separation between them.  That’s Io on the left and its shadow in the middle; Ganymede is on the right.  Credit:  Paul Stewart

This transit had the lag time at just four minutes between when the moon started to cross, and when the shadow followed, so the two were practically attached to each other.  The black and white dots were aligned perfectly right next to each other.  With the black shadow as a reference, the white dot of Io easy to pick out even on Jupiter’s white face.  Neato!

Io shadow transit
Look at how close the shadow is to the moon, so that you can more easily find the moon next to the shadow.  The transit was like this, only closer.  (Unfortunately, I did not have the GRS or a nice brown barge when I was observing.)  Credit:  Richie Jarvis

EDIT – one of my readers pointed out that he was looking at Jupiter this weekend, too, and saw for the first time that the belts were distinctly reddish.  Now that he mentioned it, come to think of it – I was paying too much attention to being able to see not just the shadow, but Io itself – but he’s right.  The bands were definitely a light brownish color for me, too.  Hints of red, maybe, but differently colored from their usual appearance to these old eyes.  Good seeing, indeed!

I wasn’t satisfied with observing just with the Mak.  Since the seeing was so darn good, I desperately wanted to give my C9.25 a go under these conditions, see what it could do, how much I could open it up in terms of magnification.  I haven’t yet had the chance to do any planetary observing with the SCT yet, having just got it in January.

It was practically a side-by-side test.  I had set up the Mak on my balcony and watched the beginning and middle of the Io shadow transit.  I pulled the Orion Sirius Pro mount out of the back of my car and brought the C9.25 OTA down from my condo and set it up on the grass in the corner of the condo property, right underneath some anti-crime floodlights (which, given the shooting that just occurred there the night before, don’t seem to work that well).  Not the most ideal location, amongst the various dog droppings, but scientific experimentation must come first!

(And yes, I realize I could have really made it a true side-by-side test by bringing down the Mak too and mounting it next to the SCT on the Orion, also (the mount has two saddles – it can carry two scopes), but, hey, it was late, and I’m a schmuck.  Oops.)

All in all, I have to say I am definitely disappointed with the planetary performance of the SCT.  It did not deliver – not at all.  It was very noticeably less sharp than the Mak, even with almost twice the operating aperture (the SCT is 235mm; the Mak operates at 120).  The amount of detail you can see in an object is directly related to two factors:  the aperture and the seeing, and I had both.  Focusing was a chore on the SCT; it was difficult to get a really precise focus.  Even with the Mak bouncing away on my concrete balcony at the slightest touch, I got a much sharper, more detailed view with it.

I tried observing both without and then with the focal reducer.  The SCT just would not take the magnification without the FR, while the Mak was lapping it up with the great seeing.  The magnifications of the various EPs I have with the Mak and with the SCT/FR combo are roughly equal, as the Mak has a focal length of about 1540mm, while the SCT/FR combo is 1480mm.  I used my 12.5mm KK Fuyiyama ortho in my Orion Ultrascopic 2x Barlow in both scopes.  The view with the Mak with this optically excellent combo at 246x was not just better but significantly better than the SCT on every object.

With the Mak, as I mentioned, both the shadow and Io were readily visible, which I was fairly amazed by.  With the SCT/FR, I could just make out the shadow, no Io to be seen, and the banding on Jupiter had less contrast.  With the Mak, I could just split Saturn’s ring in two, seeing the Cassini Division as well as the banding in the cloud tops; with the SCT, I could just get Saturn into focus.  With the Mak, I could see some albedo features on Mars; with the SCT, I wasn’t even sure I had Mars in focus because of its phase.

(The Great Red Spot was not viewable Saturday night/Sunday morning.  It rotated into view Sunday night/Monday morning, just before 3am, so I observed it then – with the Mak, at 191x, as the seeing wasn’t quite as good.)

However, this might not have been a completely fair test.  I had the Baader Moon & SkyGlow filter on the Mak.  That filter absolutely lives on the end of the 99% dielectric diagonal I use with the Mak, as opposed to the prism diagonal that came with and is optimized for use in the SCT.  I’ve noticed the significant improvement that the M&SG gives me before, making these exact features I’ve just described pop where they did not do so without the filter.  So, I’ll have to try this test again some day when I’m smart enough to really put the scopes side-by-side and use the M&SG on both.  Even though I’m sure that the SCT images will look cleaner with the filter, I still think the Mak will continue to rule the planetary roost.

But, at the end of the day, what I would have to say is that the C9.25 is sharp enough.  I didn’t get this telescope to use on the moon and planets.  I got it purely for its light-gathering ability, to let me go 1.5 magnitudes deeper to see more stuff and see it better, and it has already proven itself a winner there.  It’s sharp enough to show me those things.

This was not only my opening observing salvo for Jupiter, but for Saturn and Mars, too.  Sky & Telescope has a nifty little helper app for Mars, which shows you what side and which features on Mars are visible at any one time.  I’m not sure how completely I trust this app, as it said that Mars’ phase was 95%.  (Yes, Mars goes through some minor phasing, too.)  95% is just about full, and it definitely looked less full than that.  Stellarium had it pegged at about 88%, which made more sense given the slice that was missing.

Mars on April 28, 2018
Mars phasing.  Syrtis Major is the dark feature at left.  (It was more in the center when I saw it; this pic was taken a week ago.)  Credit:  Sean Walker

Observing it around 3am, Mars was still very low in the sky, only about 15 degrees above the horizon.  Looking at it through so much atmosphere at this altitude led to the same red, white, and blue effect on Mars I saw two years ago, caused by atmospheric dispersion.  However, by 4 and 5 am, it was well up in the sky, and I was able to see something on the surface.

Trusting the S&T app, it said that Syrtis Major was visible.  This is the same “racoon eyes” feature that I was seeing on Mars at its last opposition two years ago.  However, back then, Mars was about 18 arcseconds across; right now it’s only at 11, just over 60% of the width from back then, so the racoon eyes were not yet in full effect.  Just a coupla months to go until Mars gets nice and big – 24 arcseconds by the end of July!  Maybe I’ll finally be able to see the polar caps, a definite bucket list item.  Yay!

I don’t often observe the moon during this waning half moon phase, but it was up, so was I, it was gorgeous, (so was I!  Okay, probably not), I haven’t observed the moon in a while, and I love the moon, so why not?  Since the seeing was so terrific, I looked for some Plato craterlets.  I thought I was just on the edge of seeing the “big” one in the center, but that was probably more “wishful observing” than anything else.

I did get to see a couple of rimae that were not on my very incomplete “suggested moon items to view” list of a few months ago:  Rimae Hyginus and Ariadaeus, two lines in the moon’s surface, Ariadaeus on and Hyginus pretty close to the terminator at this phase, winding their way a few hundred kilometers from left to right.  My terrific moon book, The Cambridge Photographic Moon Atlas, describes Ariadaeus as being 7 km wide, 250 km long, and about 500 meters deep, and easy to see in small telescopes.  Hyginus is just to the east of it, a bit shorter, about 220 km long, and only 400 meters deep.

Rima Ariadaeus is a fault line, a crack on the surface of the moon due to the cooling of the moon, while Rima Hyginus consists of two lava channels flowing out from the crater/volcano Hyginus itself.  Before I was born, the hypothesis for the formation of how craters were formed on the moon were that they were generally all volcanic in nature.  Then the thinking changed as lunar geologists understood that craters were not the cones of dead volcanoes, but were instead formed as the result of asteroid impacts.

The Apollo missions revealed that the moon is a completely dead and cold world where volcanic activity isn’t possible.  Isn’t.  But not wasn’t.  Lunar geologists came to realize that some of the features we can still see on the surface of the moon date back to around 4 billion years, and they re-revised their thinking.  While all of the larger lunar craters are still the result of asteroid impacts, a very few of the smaller ones are thought to be volcanic in nature.  The 11 km wide crater Hyginus, at the center of two arms of the rima, is one of these little volcanoes, as it does not have a raised rim the way impact craters do.  The rima is what’s left of an ancient – very ancient – lava flow.  Pretty cool stuff!


5 thoughts on “May 7, 2018: Stunning Io Transit! And Planetary Disappointment with the SCT

  1. Jon, this is a really good account.
    I too own a 5 inch Mak although mine is an Orion where I believe yours is a Celestron. But its likely that both are made by Senta in Taiwan and are for practical purposes the same scope. I have long been impressed by how my Mak hits way above its weight so I am not surprised with your results. I do wonder though if your 9.25 is in tight collimation– and it is possible that seeing could have changed in the time interval between observing with the Mak and the 9.25. That would not be unusual for Colorado. Anyway, thanks for a good account.

    Liked by 1 person

    1. Thanks, Digby. I agree about the Mak – and punches above its weight is always how I describe it, too. I also use “apo-like views – at one-tenth the price”. You’re right, though – it does make me wonder how good the collimation is on the 9.25. It seems like there shouldn’t have been as much difference between the two as I was seeing, but I think at least a little of that has to do with the M&SG filter. Have you ever used it? It really does work. I will definitely look into the collimation, though, do a star test and such.


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