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chornedsnorkack
2013-Dec-17, 09:46 AM
Do planets not twinkle?

Mars shrinks to 3,5 seconds near conjunction. Mercury to 4,5 seconds near superior conjunction.

Is that big enough to not twinkle? Considering that planets near conjunction are near Sun, low in sky... is Mars low in twilight at the far side of orbit detectable as an extended object through lack of twinkle?

iquestor
2013-Dec-17, 11:27 AM
OH. I read the title as "Size Of a Twinkie" and got hungry. :(

NEOWatcher
2013-Dec-17, 12:51 PM
OH. I read the title as "Size Of a Twinkie" and got hungry. :(
Well; they did shrink on their return.

Wiki's always good for a clue (http://en.wikipedia.org/wiki/Astronomical_seeing#The_full_width_at_half_maximum _.28FWHM.29_of_the_seeing_disc).

A 1.0" seeing is a good one for average astronomical sites. The seeing of an urban environment is usually much worse [...] At the best high-altitude mountaintop observatories (http://cosmoquest.org/wiki/Observatory) the wind brings in stable air which has not previously been in contact with the ground, sometimes providing seeing as good as 0.4".

Hornblower
2013-Dec-17, 02:08 PM
I have seen Venus twinkle when near superior conjunction, though a good bit less than Sirius does under similar conditions.

grapes
2013-Dec-17, 02:50 PM
Do planets not twinkle?

Mars shrinks to 3,5 seconds near conjunction. Mercury to 4,5 seconds near superior conjunction.

Is that big enough to not twinkle? Considering that planets near conjunction are near Sun, low in sky... is Mars low in twilight at the far side of orbit detectable as an extended object through lack of twinkle?
Yes, planets can twinkle, even bright ones.

Yep. Venus rises three hours before the Sun, there, now.

The BA mentions in his book that the planets can twinkle--but if they do, it's a sure sign that the astronomical seeing will be poor. If the planets are bad, the stars will be worse. I'll see if I can recite his poem, from memory:

"Twinkle, twinkle, little planet,
Can't observe, so better can it."

glappkaeft
2013-Dec-20, 09:19 PM
It's really hard to say something that hold true generally. I have seen both Venus and Jupiter twinkle even when near opposition when the seeing has been unusually bad (like both Jupiter and Venus two weeks ago, the seeing was measured around 4 arc-seconds FWHM at zenith), especially if the planets where close to the horizon.

I have also encountered nights of almost perfect seeing where even stars around 10 degrees above the horizon (e.g. the night we first cleanly separated the e/f stars of the Trapezium and then split Sirius A/B - almost unheard of from 60N where they never rise very high) didn't twinkle at all.