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Jupiter events, 2-3 Sep

Talitha

By Talitha
in Observing - Planetary

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Talitha

Talitha

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Admittedly i'm not a planet observer, but the show Jupiter put on last night was absolutely incredible. The seeing was a bit better than average, and was what i've heard referred to as 'laminar flow' seeing. It's like looking at an image at the bottom of a crystal clear brook which, although moving, isn't creating any sort of surface disturbance. You see waviness but it doesn't spoil the view.

Anyway, when i got out to the Starpad at 8:30 the GRS was in mid-transit and due to the seeing, it was the cleanest view of it i've ever had. To the east, Europa and Ganymede looked like a double star, and Io was about the same distance from the planet but to the west. Callisto had already slipped behind Jupiter.

As the GRS slowly drifted towards the limb, the three moons pulled in closer and closer to the planet. Io disappeared behind Jupiter at about 10:40, and then Europa began it's ingress on the other limb at about 11:00. I missed those two events because, well, i'm a moonatic and Luna was so lovely last night i lost track of the time whilst gliding up and down the terminator. :)

When i checked on Jupiter again at about 11:30, Ganymede was the last man standing... the other three moons were gone. I watched as Ganymede began its transit ingress just above the northern edge of the SEB. It was awesome.. i could actually see the gradient shadowing on its leading limb, defining it as a disc. It took about 8 minutes from first contact till the completion of the ingress. While Ganymede was crossing Jupiter's limb it was a velvety peachy-beige color. So was little Europa which was already between 1/4 and 1/3 of the way across Jupiter's disc, just skirting the southern edge of the NEB. A wide view showed Jupiter floating in the sky without escort.. very odd looking indeed.

After taking a break with Luna for a bit :(, i returned to Jupiter at 12:20 and saw that Europa's shadow transit had already begun. It was a distinct dot, just like the other shadow transits i've seen through the years. But then i saw something which i'd never seen before.. one of Jupiter's moons in transit. WooHoo! Ganymede was below Europa's shadow. I've no idea why Europa retained its light color when seen earlier, but Ganymede definitely had lost the lightness and was now a diffuse, shadowy dot below Europa... soft grey.

From what i understand Jupiter won't be moonless for a long time, and i'm so glad it was clear out last night with good seeing.

And my neighbors wonder why i sit outside at night... sheesh. :D

Thanks for reading. :)

post-13732-133877395973_thumb.jpg

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AztecastroMcJ

AztecastroMcJ

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been 2 cloudy here

but couple nights ago managed quick 5-10m view about 11pm

noticed there were only 3 moons

checked stellarium and think Europa n Ganymede were joined together

or at least very close

when viewing in scope they looked like 1 moon not 2

last good conditions had try'd to image with webcam

took bout 20m to set up everthing then total cloud cover

imaging is so Annoying at times

wish i had just enjoyed the view instead

must have been strange seeing Jupiter all alone with no moons

James

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Talitha

Talitha

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Thanks, WH. :) We all need bigger scopes. :D Here's something interesting, though.. might make you feel better. I saw something a while back that calculated how much of an 8" SCT's aperture is actually usable after you subtract the secondary obstruction. Turns out it's 5". No wonder there's such a small telescopic limiting magnitude difference between the SCT and the 120 achro.

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Patw#73

Patw#73

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Great report.

I spent a considerable time last night from about 9.30 to midnight fixed on Jupiter. All the moons did their merry dance as usual but the GRS remained as elusive as ever!

Tried a blue filter, which did help bring out the bands but not a sign of the spot!

I suppose it was on the other side!

I'll keep on trying!

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The Warthog

The Warthog

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Thanks, WH. :) We all need bigger scopes. :D Here's something interesting, though.. might make you feel better. I saw something a while back that calculated how much of an 8" SCT's aperture is actually usable after you subtract the secondary obstruction. Turns out it's 5". No wonder there's such a small telescopic limiting magnitude difference between the SCT and the 120 achro.

I disagree with that math, having done the math myself a few times. If the secondary is 30% of the diameter of the objective, it's about 10% of the area of the objective. The remaining area is about the same as a 7.5" unobstructed objective, for an 8" SCT. The obstruction of a Newtonian secondary is about 5%.

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TheThing

TheThing

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Lovely report Talitha, thanks for sharing.

Great drawing too. I saw it quickly on the forum front page (while I was checking the full moon status, but that's another thread) and thought it was a photo at first!

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George Jones

George Jones

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I saw something a while back that calculated how much of an 8" SCT's aperture is actually usable after you subtract the secondary obstruction. Turns out it's 5". No wonder there's such a small telescopic limiting magnitude difference between the SCT and the 120 achro.
I disagree with that math, having done the math myself a few times. If the secondary is 30% of the diameter of the objective, it's about 10% of the area of the objective. The remaining area is about the same as a 7.5" unobstructed objective, for an 8" SCT. The obstruction of a Newtonian secondary is about 5%.

Talitha, I think I know from where the 5" comes, but it's not magnitude, it's contrast.

An 8'' SCT with a 30% central obstruction has the same surface catching area, and thus the same image brightness, as a 7.5 or 7.6" refractor, as Warthog has noted.

An 8'' SCT with a 30% central obstruction has the same image contrast as a 5 or 6'' refractor. (The central obstruction causes a change in the Airy diffraction pattern; the relative difference between the brightness of the disk and the first ring decreases as obstruction size increases.)

An 8'' SCT with a 30% central obstruction has the same image resolution as an 8" refractor. (Since the obstruction is central, the maximum separation of useful light is stll 8".)

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George Jones

George Jones

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Thanks, glad i was able to share this. :D We're used to seeing Jupiter with those familiar little fireflies buzzing around it... looked really weird without them.

I first read (a couple of weeks ago) the 5" figure for contrast in The Backyard Astronomer's Guide by Dickenson and Dyer, but without any details. Last night, I decided to Google aorund a bit, which led me to Thierry Legault's very informative pages,

Astrophotography - Thierry Legault.

Click on "The obstrusction" in the menu at the bottom left. "Collimation" in the same menu is also very interesting, and somewhat surprising, at least for me.

I have Legault's beautiful New Atlas of the Moon.

Yes, beautiful report!

I had hoped to view this through a new, small scope, but it seems that I'm getting jerked around by the shop from which I ordered the scope. If I get time, I'll start a thread on this.

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