Jupiter - Great Red Spot - an observation
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William Bottaci
May 30, 2018, 8:59:30 PM5/30/18
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We've just come in from looking at Jupiter. We used an Orion 8-inch
f/6 Dobson (F = 1200 mm) with a Skywatcher 6 mm eyepiece, which puts
the magnification at x200. This is about as high as I'd usually go,
and then only if the atmosphere allows it. Jupiter is low this year
and rises no higher than about 23°, and this is low, but the
atmosphere looked unusually steady. The image held out.
Plenty of cloud bands/belts and variations within each. There is a
particularly thin one at the same level as the great red spot, which
is causing a dent in the south equatorial belt.
The great red spot was just coming in and over the course of an hour
easily moved towards the centre/meridian. Despite news reports that
this weather phenomenon is diminishing (over the last 20-30 years) it
was easy to see and looked a deep orange/brown colour. One could
easily say red. Although it has been recorded since early telescope
times there's no reason to assume that it's a permanent feature, and
we've been taking it for granted. A shame if/when it goes completely
and not replaced with anything similar but it could just as easily not
have existed at all. What can we say? If you've never seen it, don't
delay.
At f/6 the secondary is not too large and at 8-inches the aperture is
only beginning to be affected by atmospheric turbulence, so not too
bad a combination. Contrast is what we need with Jupiter; it's plenty
big enough to otherwise see detail. Secondary obstructions count
against contrast, which is why refractors have value here, and see
more inch for inch.
Comparing with 120 mm binoculars using the same eyepieces (x110) the
view is similar, and there are pros and cons so not straightforward.
The definition would be the same, the contrast better, two eyes even
better, but the lower magnification counts against.
Within a few seconds of ten minutes passed midnight a satellite passed
from south to north. Very faint, much fainter than the 4 moons, it
actually crossed the disk. Something you have to see for yourself to
immediately believe it. Its speed was not too fast even for x200 so it
must have been very high up, and the Earth's shadow is longest low in
the south only an hour from true midnight.
About a month ago with the same binoculars I managed (quite by chance)
11 satellite sightings. Three around Messier 3, Two around Messier 51,
and two others were seen to have crossed the paths of ones I was
following. This is not that unusual.
Last year using a magnification of x27 to find Saturn I noticed what I
first thought to be an aircraft but there were not the distinct
features of coloured or flashing lights. Guessing it was the
International Space Station I was able to acquire and follow it
(4-inch alt-az mounted refractor) and then there was no doubt; the
structure of the solar panels was easy to see. Right place and time by
sheer luck, and I'd never have managed it with a higher magnification.
The Skywatcher 6 mm eyepiece, despite 5 elements, is a budget item.
Good enough and purposely for the public during outreach. I have to
say that the quality near the centre of the field is remarkable for
such a price, but it's by no means flat and so better suited for
longer telescopes. The money has gone into eye relief rather than
field of view; in my opinion a good judgement as that extra view would
be wasted, and it would have taken away from the centre.
An eyepiece giving a flat field at f/5.5 would be regarded as good
quality, but is this just a case of matching the objective? Would a
long focus objective therefore show a reverse curvature? Does the
eyepiece have to match the focal length/ratio? Anyone?
Sorry, no photos; just an old fashioned observation report.
William
f/6 Dobson (F = 1200 mm) with a Skywatcher 6 mm eyepiece, which puts
the magnification at x200. This is about as high as I'd usually go,
and then only if the atmosphere allows it. Jupiter is low this year
and rises no higher than about 23°, and this is low, but the
atmosphere looked unusually steady. The image held out.
Plenty of cloud bands/belts and variations within each. There is a
particularly thin one at the same level as the great red spot, which
is causing a dent in the south equatorial belt.
The great red spot was just coming in and over the course of an hour
easily moved towards the centre/meridian. Despite news reports that
this weather phenomenon is diminishing (over the last 20-30 years) it
was easy to see and looked a deep orange/brown colour. One could
easily say red. Although it has been recorded since early telescope
times there's no reason to assume that it's a permanent feature, and
we've been taking it for granted. A shame if/when it goes completely
and not replaced with anything similar but it could just as easily not
have existed at all. What can we say? If you've never seen it, don't
delay.
At f/6 the secondary is not too large and at 8-inches the aperture is
only beginning to be affected by atmospheric turbulence, so not too
bad a combination. Contrast is what we need with Jupiter; it's plenty
big enough to otherwise see detail. Secondary obstructions count
against contrast, which is why refractors have value here, and see
more inch for inch.
Comparing with 120 mm binoculars using the same eyepieces (x110) the
view is similar, and there are pros and cons so not straightforward.
The definition would be the same, the contrast better, two eyes even
better, but the lower magnification counts against.
Within a few seconds of ten minutes passed midnight a satellite passed
from south to north. Very faint, much fainter than the 4 moons, it
actually crossed the disk. Something you have to see for yourself to
immediately believe it. Its speed was not too fast even for x200 so it
must have been very high up, and the Earth's shadow is longest low in
the south only an hour from true midnight.
About a month ago with the same binoculars I managed (quite by chance)
11 satellite sightings. Three around Messier 3, Two around Messier 51,
and two others were seen to have crossed the paths of ones I was
following. This is not that unusual.
Last year using a magnification of x27 to find Saturn I noticed what I
first thought to be an aircraft but there were not the distinct
features of coloured or flashing lights. Guessing it was the
International Space Station I was able to acquire and follow it
(4-inch alt-az mounted refractor) and then there was no doubt; the
structure of the solar panels was easy to see. Right place and time by
sheer luck, and I'd never have managed it with a higher magnification.
The Skywatcher 6 mm eyepiece, despite 5 elements, is a budget item.
Good enough and purposely for the public during outreach. I have to
say that the quality near the centre of the field is remarkable for
such a price, but it's by no means flat and so better suited for
longer telescopes. The money has gone into eye relief rather than
field of view; in my opinion a good judgement as that extra view would
be wasted, and it would have taken away from the centre.
An eyepiece giving a flat field at f/5.5 would be regarded as good
quality, but is this just a case of matching the objective? Would a
long focus objective therefore show a reverse curvature? Does the
eyepiece have to match the focal length/ratio? Anyone?
Sorry, no photos; just an old fashioned observation report.
William
Tony Roberts
May 31, 2018, 5:33:26 AM5/31/18
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William, does the Orion have the higher specification optics?
Tiny
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Tiny
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William Bottaci
May 31, 2018, 9:23:30 AM5/31/18
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Hello Tony, I don't believe so. A little complicated because there are
two Orions, UK and US, and I think this is a US product, rather their
company because since bought by Synta and in any case made in China.
The UK Orion I think is still UK based and they are in Newcastle Under
Lyme. They're the ones that make the expensive products.
Our telescope is a Skyquest XT8 classic dobsonian:
https://uk.telescope.com/Orion-SkyQuest-XT8-Classic-Dobsonian-Telescope/p/109907.uts
and at £290 it's very reasonable; much reduced from the review price.
The review:
http://www.skyatnightmagazine.com/review/telescopes/orion-skyquest-xt8-plus-dobsonian-telescope
said it suffered from reflections from the internal tubing but
fortunately the previous owner coated the insides with black flock
paper. A previous speaker John Timmins said that this should be done
with all Newtonians.
I believe the company at one time suffered from poor assembling; I've
heard problems with the flats from two knowledgeable people.
I could tell it could benefit from slightly better collimation, so all
the more remarkable. The adjustment screws are large finger screws and
close to hand when viewing but I don't know if these were installed by
the previous owner. I didn't bother with collimating last night but
I'll have a go soon. There's no real trick to this; turn one screw,
see what it does then remember and apply to all three; and make only
small adjustments thereafter.
I don't think an 8-inch SCT can beat what we saw last night on
Jupiter; the one particular disadvantage of them is the large
secondary.
With a full Moon and this time of year there wasn't much else to see
in the time I had.
It fits in the car and we've had it at Kenley a couple of times. It
has a red-dot finder. I think a good outreach telescope; you can
almost or just about 'let them get on with it' if it comes to it. Will
bring one night to Kenley but may have to sacrifice the binoculars; I
think only room for one or the other :(.
William
On 31 May 2018 at 10:33, 'Tony Roberts' via croydonastro
Tony
On 31 May 2018 at 10:33, 'Tony Roberts' via croydonastro
Tiny2018-05-31
two Orions, UK and US, and I think this is a US product, rather their
company because since bought by Synta and in any case made in China.
The UK Orion I think is still UK based and they are in Newcastle Under
Lyme. They're the ones that make the expensive products.
Our telescope is a Skyquest XT8 classic dobsonian:
https://uk.telescope.com/Orion-SkyQuest-XT8-Classic-Dobsonian-Telescope/p/109907.uts
and at £290 it's very reasonable; much reduced from the review price.
The review:
http://www.skyatnightmagazine.com/review/telescopes/orion-skyquest-xt8-plus-dobsonian-telescope
said it suffered from reflections from the internal tubing but
fortunately the previous owner coated the insides with black flock
paper. A previous speaker John Timmins said that this should be done
with all Newtonians.
I believe the company at one time suffered from poor assembling; I've
heard problems with the flats from two knowledgeable people.
I could tell it could benefit from slightly better collimation, so all
the more remarkable. The adjustment screws are large finger screws and
close to hand when viewing but I don't know if these were installed by
the previous owner. I didn't bother with collimating last night but
I'll have a go soon. There's no real trick to this; turn one screw,
see what it does then remember and apply to all three; and make only
small adjustments thereafter.
I don't think an 8-inch SCT can beat what we saw last night on
Jupiter; the one particular disadvantage of them is the large
secondary.
With a full Moon and this time of year there wasn't much else to see
in the time I had.
It fits in the car and we've had it at Kenley a couple of times. It
has a red-dot finder. I think a good outreach telescope; you can
almost or just about 'let them get on with it' if it comes to it. Will
bring one night to Kenley but may have to sacrifice the binoculars; I
think only room for one or the other :(.
William
On 31 May 2018 at 10:33, 'Tony Roberts' via croydonastro
Tony
On 31 May 2018 at 10:33, 'Tony Roberts' via croydonastro
Tiny2018-05-31
Tony Roberts
May 31, 2018, 12:34:56 PM5/31/18
to croydo...@googlegroups.com
Hello William,
Thanks for the information. The optics are obviously good from what you were seeing yesterday.
Reference collimating, I have just returned from telescope house with a laser collimator. If you would care to try it out?
On the other hand ultimate collimation requires looking at star images as you know so if yours is close then the laser may not help at all.
Also bought 2nd hand right angle finder for Dob’. Straight through finder it came with finally exceeded my patience last weekend, I seem to be missing the necessary neck joints when above 60 degrees altitude. I might sell it on to an Owl.
Agreed on the image quality. Although I have not pushed the magnification as hard with my Dob’ as you have the image is much crisper and contrasty than same size SC and I am sure for the reason you have given.
Tiny
Sent from my iPhone
Thanks for the information. The optics are obviously good from what you were seeing yesterday.
Reference collimating, I have just returned from telescope house with a laser collimator. If you would care to try it out?
On the other hand ultimate collimation requires looking at star images as you know so if yours is close then the laser may not help at all.
Also bought 2nd hand right angle finder for Dob’. Straight through finder it came with finally exceeded my patience last weekend, I seem to be missing the necessary neck joints when above 60 degrees altitude. I might sell it on to an Owl.
Agreed on the image quality. Although I have not pushed the magnification as hard with my Dob’ as you have the image is much crisper and contrasty than same size SC and I am sure for the reason you have given.
Tiny
Sent from my iPhone
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