At Last !

This topic contains 8 replies, has 3 voices, and was last updated by  David Galvin 5 years, 7 months ago.

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  • #2783

    john Crockatt
    Registered user
    0p

    Week after week Gerrard tells us of the wonders we can see within the next day or two.  And time after time here on the Wirral we look out and all we see is the usual heavy overcast.

    He told us to look out for Mars and Regulus yesterday morning (11th)  The sky clouded over solid some time before 0300.

    But, at last, this morning at 0525 we saw them, and a very nice sight it was, though the contrast in colours was nothing like so marked as in the example Gerrard gave us,  Is it possible that our Irish friend was using some fancy filters ?

    John Crockatt

    #3314

    Brendan Martin
    Administrator
    1p

    Hi John, glad you managed to catch sight of Mars and Regulus,the colour may have been affected by atmospherics, there is a lot of moisture and of course there is the Moon to contend with.
    cheers
    Brendan

    #3315

    john Crockatt
    Registered user
    0p

    Thanks, Brendan,

    I perhaps ought to have said that Sunday 6th.November was a perfect day.  Not a cloud in the sky from the early hours of that day for a full 24 hours.

    During the day we got some good views of the sun’s spots in both the Corenado PST, and in the 4″ Skywatcher, fitted with a home-made Baader film filter.

    In the evening a fine view of the moon, which was at waxing Gibbous.  The most impressive sight was the “bay” called Sinus Iridium, which was right on the terminator, and so the semi-circular “cliffs” of the bay were brilliantly lit, with the peaks of the Jura Montes showing behind.

    Then a look at Jupiter, with our first sight of her moons.  We saw three, Europa, Callisto and Io.

    Later study  of the diagram in Astronomy Now showed that we ought to have seen Ganymede,  which was right on the southwest limb of Jupiter.

    A really good day for a pair of beginners.

    John and Angela Crockatt

    #3316

    john Crockatt
    Registered user
    0p

    In my last post I reported a good view of Jupiter.  It was rather brief.

    This evening is very clear and a couple of hours ago I set up the same telescope again for another, longer look at Jupiter.

    I focussed on Jupiter, and what I saw was a white disc, covered with black blobs and some black streaks.  Nothing I could do would change this.

    Telescope is a Skywatcher Star Travel 102mm Refractor.  Focal length is 500mm and I was using a 20mm eyepiece giving x25 magnification.

    Has anyone had this experience and can anyone explain it ?

    John Crockatt

    #3317

    David Galvin
    Administrator
    2p

    Not sure about the black bobs and black streaks but sounds like eye lashes in the way. This really does happen, as for the white disc please read on.

    The problem with our  weather is that although it is a wonderfuly clear sky and the stars are shining, you may find that the actual seeing is unsteady. This will result in a washy image with little detail visible. Couple that with tube currents and you will struggle to see any detail.

    Try focusing a star such as Polaris or Arcturus until it is a pin point and then take the focus inwards so that star image becomes a blob with rings (it should look like my avatar). You can also take the focus outwards and get a similair result. What you should see, in ideal conditions, would be a steady bullseye type effect with concentric rings.
    What you will probaly get is the concentric rings with wavering eddies of air that pass across the light path of the tube. These are, simply, thermal air currents withen the tube and should, given an hour or so settle when the scope comes to equilibrium with the outside temp.
    In our out of focus image you may also see flashing bands that move across the field of view which are caused by the bad seeing condions of the atmosphere.
    When you try to observe a focused star it may appear to ‘dance’ across the field of view especially if under high magnification. Observing the planets under these conditions can be awful with detail almost invisible, in fact a sky that is slightly hazy can often result in a better image due to the air being staedy.

    Video link that show tube currents:
    http://www.youtube.com/watch?v=Ed3fYJmgOIo

    Bad seeing due to unsteady atmosphere:
    http://www.youtube.com/watch?NR=1&v=3SOQ-NUbyUo

    #3318

    john Crockatt
    Registered user
    0p

    Many thanks, David.  Most helpful.

    Two further points.  When I saw Jupiter the other day, using the same low magnification, I saw it as a small disc, too small for any surface detail, with its moons around it.  The whole group was in the centre of the field of view, with plenty of space around it.  Last night the white disc filled the whole of the field of view.

    Secondly, referring to heat currents.   Last night I was testing another telesceope, with unsatisfactory results.  I finally gave up, and, hoping to get some observing time I got out the Sktwatcher.  My telescopes live in the garage,  which is completely dry, and now I think of it, is probably warmer than the outside temperature, tho’ it has no heating.   What we saw last night was within less than five minutes after bringing the telescope out,  and it had had no time to cool.  Could this be the explanation?

    John

    #3319

    David Galvin
    Administrator
    2p

    Not sure without actually seeing the set up but if it was exactly the same configuration that can only leave the focusing, perhaps it was way out of focus! The moons of Jupiter should be (almost) pinpoints of light whilst Jupiter would show a smallish disc (as you described) . I cant think what else it would be. The Moon will be back in the evening sky next week and you could check your focus technique on that ie craters are sharp, then check for point like stars and Jupiter as described. I would not think that your mirror is lose and cause the focus to shift.
    On your second point I would suggest that the scope did not equalise with the outside temperture. I have my scope permently set  up outside in a a shed with a roll off  roof (luxury :-) ) and even that suffers from the temerture difference when the roof is drawn back to observe. Those pieces of glass do hold the heat and take time to cool. Try and give it 30 minutes at least before expecting to much and take into account what we said earlier about tube currents and seeing conditions.

    #3320

    john Crockatt
    Registered user
    0p

    Thanks, David.  I had already resolved that I will always in future give any ‘scope time to cool down.

    I wish I could have a shed like yours. I have seen them advertised, but we don’t have the room at the point where I have to site my ‘scope.

    Regards,

    John

    #3321

    David Galvin
    Administrator
    2p

    Mine is an old 10 ft by 8 ft gareden shed with the sloping roof cut off. I fitted a set of runners on it and it works okay. Saves having to set up evert time and is operational in five mins.

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