JamesF

3 minutes ago, happy-kat said:

Could do the free open Moon course. It covered tides, and the earth itself bulges not just the water

Is that a Lancaster Uni course?  My son is hoping for an offer from them to study Natural Sciences, if Cambridge won't have him.

James

Ignoring the tidal bulge on the side of the Earth opposite the Moon and the effects of the Sun etc. for the moment, we all know it's mostly the Moon's gravity attracting the water in the oceans, right?

Well, hmmm.  I was lying in bed the other night contemplating life, the universe and everything when it struck me that I wasn't really sure that's a particularly good explanation.  (Look, just don't ask me to explain what goes on in my head, ok?  I'm not entirely sure it's all under my control in the first place.)  My thoughts followed thusly:

The Moon's gravity exerts a force on an ocean facing it, but it's nowhere near the force exerted on the water by the Earth, so the Moon can't actually move the water towards it.  It just means that the net force on the water in the direction of the Earth is reduced.  It won't be dragged "up" towards the Moon because of the Moon's gravitational pull therefore.  It will stay where it is.  So what actually causes the "bulge" of water that occurs?

Is it that due to the spinning of the Earth the water actually wants to obey Newton's first law and disappear off into space all the time, but is prevented from doing so by the Earth's gravity, though not prevented quite so much when the Moon counters some of the Earth's gravitational attraction thereby allowing it to move further from the centre of the Earth before Earth's gravity "overcomes" it?

Perhaps that's not a very good explanation either.  Assuming it's basically the correct idea perhaps a clearer explanation would be to show how all the forces involved are acting.  So it wouldn't be the Moon's gravity attracting the water, but that force changing the equilibrium of all of the others?

It leads me to another question as well: Does a given mass of water weigh the same at sea level at all points on the Earth, or does it vary depending on the position of the Moon?

Is there some other explanation?  Or should I just be taking more Valium?

James

What are peoples' feelings about the oldest version of MacOS likely to be in use these days?

I believe oacapture etc. should still run on 10.6, but maintaining a build environment for that is becoming increasingly challenging.  Moving forward a few years would probably make life simpler if people just aren't using the older versions any more because hardware has been "retired".  For instance my MacBook is seven years old and won't run anything earlier than 10.9 and not even all versions of that release.  I'm actually expecting it to "fall off" Apple's list of supported systems fairly soon.

James

On 23/09/2020 at 04:57, jager945 said:

For anyone interested, this is currently a very cheap solution (~40 GBP) to get your hands on some pretty decent compute performance, if you are currently making do with an iGPU or older (or budget) GPU.

That looks quite interesting as a way to try out some stuff I've been playing with.  At the moment I can't find a UK source at a delivered price that is close to £40 though

James

On 18/10/2020 at 05:04, Galen Gilmore said:

I just processed a picture I took a couple months ago because I only just got around to doing it. But I also just happened to stumble across an interesting YouTube video about a processing technique called the Arc Hyperbolic Sine Stretch.

I decided on giving it a go on M57, and all I have to say is WOW!

The technique did a great job of making the image feel very natural by preserving star color, and preventing them from becoming bloated.

If anyone else is interested in it, here is the video.

There are some comments in that video that bother me...

The first is one about the green histogram being further to the right because there are twice as many green photosites on his colour sensor than there are red or blue.  I'm not sure I follow the logic of that.  Surely the green histogram would shift to the right if the green photosites counted more photons, or if more than one green pixel value were added into the demosaic process without any scaling of the values used (which I don't believe will happen).  I'd guess that the reason is actually that the green photosites are just more sensitive and count more photons?

The second is the moving of the black point in the individual channels before the stretch is done.  If the point of this particular stretch is to preserve the colour balance, then surely moving the black points beforehand defeats that goal because in doing so the colour balance is changed?

James

15 minutes ago, Nigella Bryant said:

Na, Devon, where it rains eight days out of seven, lol.

My son goes kayaking with school every Tuesday, sometimes in the sea, but often on the rivers in Devon.  I think the Exe and the Dart are particular favourites.  He wasn't able to go this week because the rivers were too low due to lack of rain!

I think this morning may have corrected the situation however :D

James

Thanks for that.  I often wonder myself if I'm interpreting the output of lsusb correctly

James

Nicely recycled.  We hate most single-use plastics :)

The "Celebrations" lids certainly seem to have a bigger lip -- I have a few of these that I've recycled for storing parts for projects and so on.

James

With the camera plugged in, could you give me the results of running "lsusb", please?

Thanks,
James

3 minutes ago, Neil H said:

Hi i have a house at 90 degs to my garden with a flood light and that lites up my bedroom as light travels side ways as well so tell the council its lights up your bedroom which you may find its does then the council  will do some thing

Is there anyone whose bedroom they don't light up?!  Personally I'm more worried about airline pilots thinking there's a runway to land on.

James

6 minutes ago, johninderby said:

Found a pic of the Bresser 102 with the dew shield removed.

Well done.  I had a quick search but failed miserably.

James

I'm not sure that all dew shields are a simple push-fit, so it might be worth trying to verify exactly how it does fit before getting medieval on its donkey.

Once you're sure, if you can clamp the OTA in place then a pair of marigolds or a rubber strap wrench might allow you to apply a little more controlled force to the dew shield.  Always use the yellow marigolds, by the way.  They look so much more fetching when your other half posts a picture of you to their social media of choice.

James

Hmmm.  Not sure what might cause that at the moment.  I'll have to give it some thought.

James

7 hours ago, Dave Lloyd said:

Set up a couple of mirrors at the bottom of your garden adjusted to shine through all his windows. That way if he doesn't like it he has the means to stop it. 

I'd be quite tempted to do that in the OP's position.  I'm not sure I'd be able to fight the temptation.  I could get a nice shiny piece of parabolic steel and claim I was using it for radio astronomy or something

Not that I'm recommending it as a sensible course of action...

James

5 minutes ago, randomic said:

Amazing! Thanks so much! Is it built into the binary or is there a directory I can drop the new so to test it out locally?

oacapture should just pick the library up if it is installed (and it will use the INDI version if it is present), so you should be able to change it if you want.  Unfortunately I don't know where the version that comes with INDI is on an RPi as I don't have it installed on any of mine :(

What you might be able to do is to download the latest SDK and extract it and then set the LD_LIBRARY_PATH environment variable to the directory containing libASICamera2.so, then run oacapture:

$ export LD_LIBRARY_PATH=<path-to-directory>
$ oacapture

I'm not 100% sure that will work, but it's worth a try.

On 16/10/2020 at 20:04, randomic said:

It seems to be unsupported in most software at the moment, for example: FireCapture, oacapture

I'd guess that's because there's a new release of the ZWO SDK that I've not got built into oacapture.  I'll make sure that's done for the next release.

James

Come to think of it, once I get a bit more organised with stuff the possibility of offering one of our fields here as an observing location if people are interested.  On good nights I reckon NELM can be between 5.5 and 6 based on stars in UMi.  Driving onto the field probably wouldn't be clever if there'd been a lot of rain recently and there's no electricity or anything like that (maybe one day), but there would be the opportunity to chuck a tent up and get a few hours kip after a hard night at the eyepiece.  Just need to get our building work all finished off first...

James

17 minutes ago, M110 said:

Following giles' links above I came across a "Dark Skies Pocket Guide" (here) produced by the Exmoor National Park which actively encourages astronomy and gives specific examples of suitable sites - one of which is the Haddon Hill site @cheddar-man suggested.

I live under the "To Taunton and the M5" text on their map.  I've been to Wimbubble Lake a few times when my son has been canoeing/kayaking there and I'm not convinced about it as an observing site unless access from the car park to the area around the lake is possible (there's a gate between the two as far as I recall).  The car park itself faces east-ish and overlooks the lake, but is surrounded by mature trees so may not be a great location unless it fits in with the targets you have in mind.  There's a sloping grass area that runs down to the water's edge and if you can get onto that I reckon it would be much better.  Vehicles do go down that far (to get boats in the water, for example).  I just don't know if they lock the gates at night.

Haddon Hill seems like a fair bet, though some of the car park does have trees to the immediate south (but not all of it).  And it should be relatively painless to get to compared with some of the other locations.

I've not been to the other sites, but my inclination would be to avoid the more northerly ones as there can be a fair bit of sky glow from further up the Severn if the air isn't perfect.  Even here, when the atmosphere is a bit moist there can be very obvious glow to the north from the likes of Cardiff and Weston-super-Mare.

James

It's not widely known, but John has quite a large collection of handles, some of which he's attached telescopes to :)

James

They look very interesting scopes, but that's a "cricket ball to the gentlemen's area" level of eye-watering looking at the price difference between the solid tube 8" and the truss tube 10".  Not that I'm saying it isn't justified, but I looked along the models taking in the prices of the smaller ones thinking "If I bought one I could be tempted to go a bit larger perhaps" and then my eyes came out on stalks when I saw the price of the 10"

James

Not a piece of software I'm familiar with, but if he's just called it a day and doesn't want to do anything more with it, it's a shame not to at least release the source and stick it on Github or somewhere similar.

James

Welcome from just over the border in Somerset

James

16 minutes ago, Stuart1971 said:

Just get an raspberry PI stick it on the mount with Astroberry installed and let that control everything, and VNC to that from your PC indoors, no need for a fancy PC on the mount at all....👍😀

I think that was where Paul started...

James

Ah, it could be that I am confusing the two.  I just remember something someone posted recently about connecting to the desktop of their remote RPi and not seeing apps that were displayed on the RPi monitor.  It turned out that whatever system they were using to connect actually created a virtual desktop.  I thought that was VNC, but it could have been RDP.

James

Doesn't the VNC server create a virtual display when you start it?  For some reason I thought it did.  I'm sure there shouldn't be any need to have a display connected to get the system to boot (unless there's something in the BIOS that stops the system booting if it doesn't have certain peripherals connected).

James