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michael8554

Observing stars during the day ?

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Could you find a particular Mag 1 star during the day using an 18th Century telescope on the heaving dock of a sailing ship?

I've been reading the book that goes with the recent "Longitude" exhibition at Greenwich.
I hadn't realised that by the 1760's, as well as the Harrison H4 watch, several other practical methods of determining Longitude were being tested by the Longitude Board.
One involved measuring the angle or distance between the moon and a known star at certain times.
The Astronomer Royal Nevil Maskelyne was very enthusiastic and regularly published Almanacs containing the necessary information including 10 stars that "could be seen during the day". 
These "clock stars" are:
Alpha Arietis (Hamal) Mag 2
Aldebaran Mag 1
Pollux Mag 1.2
Regulus Mag 1
Spica Mag 1
Antares Mag 1
Alpha Aquilae (Altair) Mag 1
Beta Capricorni (Dabih) Mag 3 
Formalhaut Mag 1
Alpha Pegasi (Markab) Mag 2
Now on dry land with a goto telescope I might have a chance, but what do you think?
Michael

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I think there's a pretty good chance of seeing our star, then nothing else.

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Have seen the Pleiades through a 16" SCT in daytime.   Focused and 'parked' from the previous night.

Seems a bit of a stretch from a ship back then.  Maybe in twilight etc...

Cheers

Paul

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It's surely the moving deck that's the biggest problem. I watched a shadow transit of Callisto earlier in the year with a stunning view of the shadow and the Jovian cloud belts - in the mid afternoon of a stunningly sunny day. But not from a ship. This was with a 0.8 metre Ritchey Chrétien.

Dava Sobel does rather exaggerate the success of Harrison above all other methods, perhaps, and in a nautical history I read that early Harrison watches were not all that reliable.

Olly

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Also the reasons why Harrison was denied the prize for so long.

The Board wanted a solution that could be rolled out to naval and merchant shipping.

Harrison wanted to keep the designs and watches to himself, so the rules were changed.

Once persuaded to divulge the designs they were disseminated fairly widely.

As a result the costs came down and improvements rolled in.

The Moon Distance solution met the Board's criteria and was used to make adjustments to the ship's watch.

Possibly only used at landfalls.

There was another even more accurate astronomical solution.

This involved observing the position of Jupiter's moons.

Definitely only on land.

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I've seen Saturn in the daytime through my 250px tracking on an EQ6. At the time, it would have been below the visual brightness of a number of stars such as Arcturus, Vega, Capella and Rigel. However, all of these are brighter than mag 1. It's something I quite fancy testing. I suppose Spica would be the best candidate as a close to mag 1 star.  hmmm...

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There was an article in I think Sky & Telescope a while back about daytime viewing of stars and planets.

The question was could you find those objects during the day without goto?

Michael

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I'm sure you can see those stars during the daytime. I have friends who go daytime planet watching as a fun lunchtime pursuit. Venus, Jupiter, and Saturn are their targets. Here's an image of M57 in daytime: http://www.astronomy.com/sitefiles/resources/image.aspx?item={695A71D2-A1ED-4831-820A-18212C059E5F}

I'm having massive problems believing this. I've seen Venus naked eye at midday, but it took some very careful planning. I've seen Jupiter during the day through a telescope. But a 9th mag planetary nebula in daylight. Sorry, no.  No way, not ever, not nohow.

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It's been well established that people have seen stars during broad daylight - when viewing from the bottom of a deep shaft, such as a mine or well. This would lead one to conclude that the surrounding ambient light is the major hindrance to such observations. But an interesting experiment could be conducted: Lock an accurate mount/scope on a bright star close to the East, at sunrise, so it will be near the zenith at mid-day. Then return and check that the star is still in the FOV of the scope. Now try to spot the star with just your eyes. From there you could try various other tricks such as using just a hollow-tube to shield from ambient light. Etc.

Clear Skies,

Dave

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I'm having massive problems believing this. I've seen Venus naked eye at midday, but it took some very careful planning. I've seen Jupiter during the day through a telescope. But a 9th mag planetary nebula in daylight. Sorry, no.  No way, not ever, not nohow.

Nobody said you'd see it by eye. It was photographed during the day. Different ballgame, that.

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It's been well established that people have seen stars during broad daylight - when viewing from the bottom of a deep shaft, such as a mine or well. This would lead one to conclude that the surrounding ambient light is the major hindrance to such observations. But an interesting experiment could be conducted: Lock an accurate mount/scope on a bright star close to the East, at sunrise, so it will be near the zenith at mid-day. Then return and check that the star is still in the FOV of the scope. Now try to spot the star with just your eyes. From there you could try various other tricks such as using just a hollow-tube to shield from ambient light. Etc.

Clear Skies,

Dave

Sadly, this is a myth. One of those which won't lie down and die. There was a comprehensive debunking in the Journal of the Royal Astronomical Society about 30 years ago, and again about 5 years later in the Journal of the BAA. The investigator and author of the original article, if I remember correctly, was Dr David Hughes (now Professor of Astronomy at the University of Sheffield).

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Nobody said you'd see it by eye. It was photographed during the day. Different ballgame, that.

Not THAT different! If this was possible, I'm sure our intrepid imagers would have produced more images of deep sky objects taken during the day.

I would challenge our superb imagers on this forum to produce something similar under similar conditions. The caption states that the image was taken from Ottawa shortly before 7pm in June. Ottawa is at 45 degrees north, and at 1900 on 15/6, the Sun is 8 degrees above the horizon there. M57 would at that time be 18 degrees above the horizon.

If any of our imagers can produce a convincing image of a ninth magnitude deep sky object at a similar altitude with the Sun at a similar altitude then I will (very happily!) admit that I'm wrong, and what's more, I'll owe them a pint!   :grin:

I genuinely hope that I lose this bet!  :laugh:

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There are some images here of M42 taken during the day using an Ha filter, not long after sunrise. Magnitude isn't relevant for DSOs, surface brightness is. M57 has a higher average surface brightness than M42, so it would certainly be possible to get something. Atmospheric transparency would be especially important with the Sun shining on it, if conditions were excellent and the Sun was low down I can believe the M27 image could be genuine.

Edited by Knight of Clear Skies
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M57 is probably the ideal candidate for this. It's compact and bright (yes, and it has a high surface brightness).  Go for it, guys!

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I too would be curious to see independent verification of the Ring image. What I find surprising about that image is the hint of colour. I would expect you'd need some pretty heavy averaging and low noise gear to get a daytime shot of the RIng during the day. This is only going to be harder if you start doing the imaging in colour. The lack of any stars in the image I find less surprising, since there are no bright ones in the immediate vicinity.

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