Sunday, March 17, 2019

The Moon

Moons, actually.

Ours and Jupiter's.  These moons were the targets of observation for this astronomy session.

"Why moons?" you ask?

Well, it has been many weeks since we had a break in the clouds sufficient to support dragging out the equipment for an astronomy session.  Withdrawal symptoms were manifesting themselves.

This Sunday morning, there was such a break.  Sadly, the Moon was 80% illuminated and dominating the sky.  It was so bright that it was like being under the sky in a light polluted city.  Almost all of the stars were washed out!

I decided to embrace the Moon's presence and use it as an opportunity to play with the equipment.  It was bright enough that I almost didn't need to use any other sort of lighting during the session.

It also turns out that at 0515 EST, Jupiter's moon, Io, was going to make a transit preceded by its shadow.  If you've never watched a shadow of one of Jupiter's moons slowly creep across its face, you are really missing something exciting! 

I had the equipment outside by 0100 EST and started with our Moon.  I figured that I'd spend time there while waiting for Jupiter to rise.

Our Moon

I'm really happy with the field of view offered by the ZWO ASI294MC imager.  I was easily able to capture data of the entire Moonface.  I suppose I was less happy with how quickly the data chewed through the laptop's disk space.  😒

Click on the images to view them in a larger size.

Green Cheese

The imager, coupled with FireCapture, did a great job.  I selected a region of interest on the terminator and zoomed on some craters lurking in the shadow.

Hmm, I wonder where we parked?
I spent a couple of hours playing with the equipment and the Moon, but still had some time to kill before Jupiter rise.


A skunk did cause some excitement as he poked his nose into our open garage, triggering the motion activated lights.  He stopped, confused by the sudden incandescence.  I saw him and gently "shooed" him away -- from afar, and out of range of his potential spray.

Deep Space Objects Under A Bright Moon

Sure, it's not easy, but it can be done.  All it takes is a sensitive imager and some tweaking of the electronics via laptop.  I'm betting that some optical filters could help, but I have yet to add any that'll fit the 2" bore of the ZWO ASI249MC.

I panned the sky, using the joystick to move the telescope, while keeping an eye on SkySafari.  I left the imager in place, so when SkySafari indicated that I was near something interesting, I could do some live stacking for a quick peek.

Here is one of my favorites from this morning.  It's the Leo Triplet.

M65, M66, and NGC3628
You can see how the Moon's brightness washes out the image, but the Leo Triplet is clearly there!

Jupiter's Moons

Finally, Jupiter rose above the horizon.

I really love watching the dance of the Galilean moons.  I always take a peek at Jupiter, when it is in the sky, just to see the moons.

Here is this morning's view.

From left to right diagonally, Ganymede, Europa, Io, and Callisto
The image is slightly overexposed to allow the moons to show up in the image.

It is the moon, Io, that made the morning's transit across Jupiter, with its shadow preceding.  The image above is from just shortly before the beginning of the shadow making its appearance!

I changed to my ZWO ASI224MC imager to capture the transit.  It is a really good planetary imager.  To get the necessary magnification, I put a barlow in the optical path.  Overall, the magnification was about 450x.

Io's shadow and the Great Red Spot

Io's shadow shows clearly in the upper cloud band!  As a bonus, the Great Red Spot was visible too!

It's not that great of an image, but I'm happy with it.  The seeing conditions were predicted to be "poor," and Jupiter was pretty low in the sky.  There was plenty of atmospheric murk in the way.

Next time?  Hoping for a clear dark night with excellent seeing!


  1. I used to wonder why they called the moon "green cheese" when it's kind of white-yellow-grey. Then I found out "green" meant "unripe," not the color!

    Pretty cool images! Thanks for posting.:-)


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