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Old 18-09-2017, 01:00 PM
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Tinderboxsky (Steve)
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Daylight lunar occultation of Venus

I did not think I had a chance of viewing this event today. There was fast forming and moving medium level cloud with a lot of high level haze and close to gale force winds. I set up in our rear courtyard for some wind protection.

A large cloud bank at least did it’s job by hovering firmly in front of the Sun for the duration. The edge of this cloud bank retreated sufficiently to expose the Moon and Venus for the final the 15 minutes of approach. Venus was bright and jewel like and the faint and very fine crescent Moon only just visible in the high level haze. The disappearance was to occur near the end of the fine crescent and that part of the crescent was almost invisible making it appear like a disappearance on the dark side. Venus took about 10 seconds (I was not counting) to fade progressively as the Moon’s limb slowly slid across Venus.

Whilst waiting for the re-appearance, I thought I should try for Mercury, Mars, Jupiter and Saturn as they are all in the day time sky at the moment. 
I slewed to Mercury (closer to Sun) - it was fainter than Venus but still jewel like. Mars was only 1 degree further east but was not visible through the haze. A pity as the pair would have been a nice catch in the same 2 degree FOV. I tried Jupiter on the east side of the Sun but it was hidden by too much high haze. There was too much cloud low in the east, so I did not even try for Saturn.

The Venus re-appearance was tantalisingly hidden behind the fringes of the hovering large cloud bank. So I missed the re-apperance. A very small break gave me a glimpse of Venus and the crescent Moon 90 sec after the re-appearance.

Scope: Vixen ED103S with Panoptic 24 giving 33X. Perhaps a photo tells a better story!
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Old 19-09-2017, 04:43 PM
Tropo-Bob (Bob)
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Thanks for the update Steve, it was a good read, as always.

Clouds here yesterday, rain here most of last night and today.
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Old 20-09-2017, 10:00 PM
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DeepSkyBagger (Patrick)
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Nice one, Steve. That's a good catch. In my 40 years+ of observing, I've never seen a daylight occultation.
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Old 21-09-2017, 06:09 AM
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Interesting.

How did you look up those planets ?

I use the EQ mount and setting circles assisted by Stellarium or Skysafari on my cellphone to look up daylight objects using an ED 110. Very easy, although Mars (+2.0) should be tedious in daylight these days.
But last summer (end Feb) I found Mars easliy around noon rather close to Venus.
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Old 21-09-2017, 11:38 AM
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Tinderboxsky (Steve)
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Thanks Bob.

Quote:
Originally Posted by Tropo-Bob View Post
Thanks for the update Steve, it was a good read, as always.

Clouds here yesterday, rain here most of last night and today.
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Old 21-09-2017, 11:44 AM
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Tinderboxsky (Steve)
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I enjoy chasing these events as they provide a completely different visual experience. The background sky is a bright blue and Venus (or a bright star) are bright and jewel like. This contrasts with the Moon that is quite faint, lacking in contrast and quite ethereal looking.
This is my second daylight Venus occultation. I have observed a Spica occultation in broad daylight, but my more memorable observation was an occultation of Regulus at sunrise. The disappearance (bright side occurred 17 minutes before sunrise and some fine high cloud provided a some striking pinks in the sky background. The re-appearance (dark side) occurred 20 mins after sunrise, providing a very different experience.
I have attached two photos I took at the time that give a feel for this. Sorry, they are low resolution copies but they give a sense of the change between disappearance and re-appearance. The scope is my larger NA140SS on a Trex mount.

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Originally Posted by DeepSkyBagger View Post
Nice one, Steve. That's a good catch. In my 40 years+ of observing, I've never seen a daylight occultation.
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Old 21-09-2017, 11:52 AM
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The scope is mounted on an Ioptron MiniTower Pro goto mount. It is almost completely obscured behind the scope. You can see that I have made a wooden pier extension to ensure the scope does not hit the tripod legs when slewing.
The initial alignment was done as a "one star alignment” using the Sun, with the right filters in place of course. These mounts are extraordinarily accurate on a one star alignment if care is taken to get the mount level.


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Originally Posted by skysurfer View Post
Interesting.

How did you look up those planets ?

I use the EQ mount and setting circles assisted by Stellarium or Skysafari on my cellphone to look up daylight objects using an ED 110. Very easy, although Mars (+2.0) should be tedious in daylight these days.
But last summer (end Feb) I found Mars easliy around noon rather close to Venus.
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Old 22-09-2017, 02:55 AM
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Quote:
Originally Posted by Tinderboxsky View Post
The scope is mounted on an Ioptron MiniTower Pro goto mount. It is almost completely obscured behind the scope. You can see that I have made a wooden pier extension to ensure the scope does not hit the tripod legs when slewing.
The initial alignment was done as a "one star alignment” using the Sun, with the right filters in place of course. These mounts are extraordinarily accurate on a one star alignment if care is taken to get the mount level.
I do almost the same, I use a two star alignment: the Sun and a virtual star: the zenith. The tripod should not be level, but the inclination of the polar axis should equal the latitude, set with an inclinometer or a DIY latitude wedge and then I set the telescope exactly vertical with a bubble level and reset the RA circle (0h) and the decl circle to the latitude.
Then I point to the Sun using its declination and hour angle and rotate the mount until the Sun is in view (obviously not with my eyes behind the eyepiece).
When the Moon or Venus is available, I use one of these which can be done without safety precautions.
Then it is ready to look up objects by declination and hour angle found in sky mapping apps.
With an altazimuth scope (my 80mm or my 400mm Dob) I have a DIY azimuth circle on both scopes and use an inclinometer to the altitude, which works fine, but in that case both axes have to be adjusted repeatedly. In that case the tripod / rockerbox should be level, and alignment on correct azimuth takes place with bright objects as well (although the Sun in a 400mm Dob is a real fire hazard....).

Here my page on this: https://www.skysurfer.eu/daystars.php
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Old 22-09-2017, 11:09 AM
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Tinderboxsky (Steve)
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Quote:
Originally Posted by skysurfer View Post
Thanks for your link. I enjoyed the read and your helpful instructions and observations.

I had not thought of chasing the brighter double stars - I’ll try the brighter southern ones and let you know how I go.

I see you listed your observation on 20th August 2016 for the Venus-Jupiter-Mars conjunction. I was also following this conjunction and was fortunate to get clear skies on the morning of closest approach of Venus and Jupiter on the 28th. My observation was at 10.25am. Venus was a bright jewel with Jupiter a faint, but distinct disc hovering 6 arc minutes away. Mercury was out of the field of view of course - 5 degrees away. I missed the earlier closest approach point of 4’ at about 8.30am due to cloud.
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Old 23-09-2017, 08:52 PM
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I just (it is around noon here) saw Mercury, Venus, Mars and Regulus with the ED110. The air was somewhat turbulent, and Mars was very tedious and lost him easily.
Eyepiece: Nagler 13T6 (59x).

Quote:
Originally Posted by Tinderboxsky View Post
I had not thought of chasing the brighter double stars - I’ll try the brighter southern ones and let you know how I go.
Well, Alpha Centauri and Alpha Crucis are easy ones, for you they are 24/7 available, recently I saw both easily with the ED110 in full daylight, incl companion.

Last edited by skysurfer; 23-09-2017 at 09:06 PM.
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