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Why Venus does not look crisp while observing?

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#1 saptharishi

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Posted 14 September 2013 - 12:27 PM

Encouraged by the beautiful views of Jupiter and Saturn, I thought I will get a great experience of observing Venus. I was using TOA 130 and ethos 10mm. The view was good and the image was sharp. However, when I changed to 6mm ethos, Venus was not at all sharp/crisp. To ensure my set up is fine, I slewed the scope to view Saturn and it was magnificent and vey crisp. Slewed back to Venus, it was hazy again. Any thoughts? Thanks.

#2 brianb11213

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Posted 14 September 2013 - 12:56 PM

Encouraged by the beautiful views of Jupiter and Saturn, I thought I will get a great experience of observing Venus. I was using TOA 130 and ethos 10mm. The view was good and the image was sharp. However, when I changed to 6mm ethos, Venus was not at all sharp/crisp. To ensure my set up is fine, I slewed the scope to view Saturn and it was magnificent and vey crisp. Slewed back to Venus, it was hazy again. Any thoughts? Thanks.

Probably the 6mm is giving too much magnification for the seeing state you had. Dim objects never seem to be as much affected by seeing as brighter ones, and Venus is about the brightest thing there is (apart from the Sun) in terms of surface brightness.

Not sure what scope you're using but there is little point in going above about 1x per mm (25x per inch) of aperture when observing Venus. What markings there are are very subtle and are harder to see when too much magnification is used because of the reduced contrast gradient.

#3 Alfonso

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Posted 14 September 2013 - 04:03 PM

When I view Venus I usually add an ordinary moon filter to the eyepiece. While the original brightness and CA do not bother me I find that when viewed with an eyepiece and the brightness reduced the view I have is sharper than without one. I can see the entire disk, if using an eyepiece of appropriate magnification, both illuminated and dark and I love this view. It's just like looking at the moon ( which I view without a moon filter). Venus to me is a golfball flying through space and as stated above when viewed my way I almost always get a crisp and clear focus and I am fascinated and thrilled by the phases this planet goes through. My scopes are: stellarvue 80mm f9, celestron 102GT f9.8 and orion XT8 f6. There is I'm sure the effect of the heat of the atmosphere having some effect on seeing but nonetheless a 'subdued' view with a moon filter is my preferred method for viewing Venus.

Alfonso

#4 Asbytec

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Posted 14 September 2013 - 10:36 PM

The responses above seem to be speaking to irradiance. Venus is very bright. It's much like looking at Sirius and trying to see diffraction rings or the "pup." The irradiance of Sirius, it's brightness on the retina, make such observations difficult. It would appear Venus has the same affect. Seeing doesn't help.

#5 brianb11213

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Posted 15 September 2013 - 04:06 AM

The responses above seem to be speaking to irradiance. Venus is very bright. It's much like looking at Sirius and trying to see diffraction rings or the "pup." The irradiance of Sirius, it's brightness on the retina, make such observations difficult. It would appear Venus has the same affect. Seeing doesn't help.

Yeah ... I've practically given up looking at Venus against a darkish sky. Full daylight or very bright twilight works for me. A valuable side effect is that the planet is higher in the sky, so the seeing is better than it is close to the horizon. When I do look at Venus in a darkish sky (usually at an outreach event) I use a very thick neutral density filter, ND 1.8, to cut the glare down.

#6 saptharishi

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Posted 15 September 2013 - 06:18 AM

Thanks so much for the responses. I will try with the Baader Moon and Skyglow filter.

#7 Rick Woods

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Posted 15 September 2013 - 09:36 AM

Is Venus low in the sky when you're looking at it? That won't help any!

#8 E_Look

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Posted 15 September 2013 - 05:58 PM

For me, it's position in the lower atmosphere makes it shake, shimmer, flare, and flare in different colors most often.

#9 Rick Woods

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Posted 16 September 2013 - 10:05 AM

For me, it's position in the lower atmosphere makes it shake, shimmer, flare, and flare in different colors most often.


(Digression:) A few years ago I got a "Risley prism" accessory, which corrects for the atmospheric dispersion (color flaring). I tried it one morning on Venus, just after it rose in the east. Without it, the image was split into three distinct colors (red, white, blue), all brilliant. With the corrector, I was able to merge them into one white image, perfectly sharp except for some wavering. A remarkable device - I expect it to come in very handy during the upcoming Martian apparitions when Mars is low in the south.

They are still available from one vendor (not the one I used), but I can't remember the name. There are some old threads in this forum about them, if anyone is interested. Mine was called the "PADC", so searching on that might help.

#10 Qwickdraw

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Posted 16 September 2013 - 11:44 AM

I am also going to guess that Venus was lower in the horizon than both Jupiter and Saturn?

#11 SporQ

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Posted 16 September 2013 - 02:24 PM

Hello,

Right now, Venus is right below Saturn, and both are much lower than Jupiter.

#12 Special Ed

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Posted 16 September 2013 - 05:06 PM

Yeah ... I've practically given up looking at Venus against a darkish sky. Full daylight or very bright twilight works for me. A valuable side effect is that the planet is higher in the sky, so the seeing is better than it is close to the horizon. When I do look at Venus in a darkish sky (usually at an outreach event) I use a very thick neutral density filter, ND 1.8, to cut the glare down.


Brian has the ticket here. And Venus is easily visible in your finder scope at the start of twilight.

#13 azure1961p

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Posted 16 September 2013 - 07:25 PM

I've read about the Risley . Surprised it isn't more popular. I'd like to get one.

Pete

#14 star drop

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Posted 16 September 2013 - 07:49 PM

Seeing, aerosols and differential atmospheric refraction all contribute to the lack of crispness. It was mentioned above of an adjustable prism assembly that can compensate for the refraction. The only source that I found online was Astro System Holland's Atmospheric Dispersion Corrector.

#15 saptharishi

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Posted 17 September 2013 - 12:18 AM

Hi Rick and Ed, you are right. Venus was low on the sky






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