M101 - The Pinwheel Galaxy

[Graeme]

Here's Messier 101, the Pinwheel Galaxy. A large spiral galaxy, 21M light years away, near the handle of the Plough asterism in Ursa Major.

Compiled from 20 x 5 minute exposures last Saturday night. It's a bit washed out by the light of the full Moon but it still came out quite well!

M101_Pinwheel_Galaxy-02-EL.jpg

Regards

Graeme

[HansV]

Wonderful, thanks!

[Graeme]

Cheers Hans.

The telescope front lens started to mist up on the final three frames due to high humidity so I might try processing it again without that data. I usually get the hair drier out when that happens! But the prime purpose of the night was to see if the sharpness improved with the infrared light on the security camera switched off. Probably not the best time to test that with a full Moon going on!

[ChrisGreaves]

Here's Messier 101, the Pinwheel Galaxy. A large spiral galaxy, ...

Graeme, if I have understood part of these processes, you have some sort of motorized mount that continually moves the lens so that the camera remains pointing directly at the object.
If this is so, is the motor controlled chronologically, or does it receive feedback from the camera so as to maintain a fixed position relative to some stellar object?
Thanks, Chris

[stuck]

...you have some sort of motorized mount that continually moves the lens so that the camera remains pointing directly at the object...

In a word, yes. Meanwhile, until Graeme responds with a proper answer, here's some background reading for you:
https://en.wikipedia.org/wiki/Equatorial_mount
https://en.wikipedia.org/wiki/Equatorial_platform

Ken
edited to add: toys like this are not cheap, e.g.:
https://www.skyatnightmagazine.com/advi ... otography/

[Graeme]

My telescope does indeed sit on top of an equatorial mount. It has two motors, one to control up and down (declination) and one to move the telescope to counteract the Earth's rotation. (Right ascension) If I use it for visual astronomy the RA motor would keep the target in view chronologically as it's set to a sidereal movement speed. As the target slowly drifts out of view, observer hand to eye feedback steps in with a tap on the hand controller slew buttons.

Astrophotography has to be more accurate to stay exactly on target all the time. The Mount has to be set up with very accurate polar alignment. The celestial pole is about 44' of arc from Polaris. I use a piece of software called NINA that controls the mount and the camera, it has a brilliant polar alignment routine which can get me to within a few seconds of the pole. But it's not possible to get it perfect, so in addition there's a guide scope that sits on top of the telescope with a second camera in the end of it. Another piece of software, PHD picks a star near the main telescope target and sends pulse signals to the mount to gently nudge it to keep that star on the cross hair to ensure the main telescope is always on target.

Good guiding is crucial for a good image.

[Graeme]

Ken
edited to add: toys like this are not cheap, e.g.:
https://www.skyatnightmagazine.com/advi ... otography/

Have you bought one yet Ken?

[stuck]

...Have you bought one yet Ken?

No, still dreaming though

[ChrisGreaves]

... one to control up and down (declination) and one to move the telescope to counteract the Earth's rotation.

So this scheme is what I labeled chronological, correct? That is, it works 24 hours a day, is not dependent on obtaining a position relative to a chosen star?

... The celestial pole is about 44' of arc from Polaris. ... picks a star near the main telescope target and sends pulse signals to the mount to gently nudge it to keep that star on the cross hair to ensure the main telescope is always on target.

Whereas this scheme depends on a stellar object. That is, only works at night time? Or more correctly when stars are visible (nighttime, no clouds, etc)

Thanks, Chris

[Graeme]

... one to control up and down (declination) and one to move the telescope to counteract the Earth's rotation.

So this scheme is what I labeled chronological, correct? That is, it works 24 hours a day, is not dependent on obtaining a position relative to a chosen star?

Kind of yes and no! A motorised mount will go all day but a computerised motorised mount needs to know where it's looking, even for visual. So they both need their RA axis pointing at the celestial pole but the computerised mount further needs to be told where at least 3 known stars are so that it can orientate itself and slew automatically to the objects in it's database.

The celestial pole is about 44' of arc from Polaris. ... picks a star near the main telescope target and sends pulse signals to the mount to gently nudge it to keep that star on the cross hair to ensure the main telescope is always on target.

Whereas this scheme depends on a stellar object. That is, only works at night time? Or more correctly when stars are visible (nighttime, no clouds, etc)

Yes.

Have you got a telescope that you're thinking of motorising?

[ChrisGreaves]

Have you got a telescope that you're thinking of motorising?

So both types of system require visible stars, that is, cloudless nights, correct?

I am not rich enough to own a telescope, and if I had one I couldn't use it in Bonavista to see the stars. Every house brags about the number of floodlights it can trigger automatically whenever a cat walks through the yard. Also sodium streetlights etc.

I was thinking that the next time Alfred Stead drives his car into my house, I would use the insurance money to fund an expedition to the Polar regions, instead of throwing it into house maintenance. I thought of sending some bright youngster to the North Pole to take a 24-hours panoramic of the midnight sun, but it seems that the technology woudn't be able to take a photo of the sun without the sun not being there.
Too bad; I would have sprung for a couple of cases of your favorite Ale, too.

In summary, then, your particular technology only works 100% with a starry night, and while the motorized doo-dad would be sufficiently accurate for my needs (just the motorized thing), the day-time technology is separate from and different from the night-time technology.
Cheers
Chris

[HansV]

So both types of system require visible stars, that is, cloudless nights, correct?

On a cloudy night, you wouldn't see the Pinwheel Galaxy...

[Graeme]

I thought of sending some bright youngster to the North Pole to take a 24-hours panoramic of the midnight sun, but it seems that the technology woudn't be able to take a photo of the sun without the sun not being there.

Not too sure about the triple negative! But the sun would be there all day and all night around the time of the summer solstice in the land of the midnight sun!

[ChrisGreaves]

Not too sure about the triple negative! But the sun would be there all day and all night around the time of the summer solstice in the land of the midnight sun!

June 21st at the North Pole, with the sun visible all day, overpowering the starlight, your system with two mechanisms would not be able to function, because both of your systems require stars to fix on.
I think that that is correct.
Cheers
Chris

[Graeme]

That's a very good point! If I took my equipment to the North Pole I would struggle to set it up. At home there are three dints drilled into the brick patio that I put the tripod legs into. The mount has micro switches that allow it to have a home position and know the direction of the celestial pole on the assumption that it points North and my latitude is set. I could set up at another location with a smart phone to tell me my latitude, the direction of magnetic north and the variance to true north. So I suppose it would be possible a few miles South of the North Pole!

As for Solar observing, I did capture an image of the transit of Mercury a couple of years ago but I can't remember how I set everything up! Roughly polar aligned would suffice for a short duration image of a bright object like the Sun and and Moon. Arc second precision wouldn't be required, a quality mount's sidereal tracking ability would suffice.

So your North Pole 24-hour panoramic of the midnight sun would be possible as long as; the set up was a bit south of the pole somewhere, you stayed awake to correct the periodic drift, you took along a heated rotating dome to stop everything from freezing up and you had a hard drive the size of a house.

:sun:

[ChrisGreaves]

So your North Pole 24-hour panoramic of the midnight sun would be possible as long as; the set up was a bit south of the pole somewhere,...

So AT the pole, one would need a device (laptop or smartphone) that kept track of the passing time and nudged a precision motor along every three or four seconds?
Or else a photocell-that-won't-burn that tracked the sun itself and nudged the camera every three seconds or so.
Of course, since one would not be interested in the sun itself as much as the panoramic view, with the camera facing away from the sun by 180º one could track the shadow of the tripod (as a gnomon) with full-on illumination of the scene, I suppose.
Cheers, Chris

[PJ_in_FL]

... and you had a hard drive the size of a house.

:sun:

How much data does your system gather per second?

I recently purchased a pair of 8TB external drives which were MUCH smaller than my house. In a 24 hour period, to fill one up would take a data rate of over 92.5 MEGABYTES per second. That's a lot of image data!

What's the estimate of how much data would really be gathered in a 24 hour continuous observation?

[Graeme]

How much data does your system gather per second?

Good observation PJ.

The M101 image comprises 90 frames all at about 23Mb each. So about 2Gb in 3 hours.

Lunar and Solar images are usually recorded in video using the SER format. The last Lunar shot I did was 500 frames (at about 15 frames per second from memory) which saved as a 5.5Gb file. So, about 180Mb/s.

Houses in Kent are quite small!