Stellarium

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Re: Stellarium

Postby Ian Pegler » Tue Mar 30, 2010 9:51 am

Version 0.10.4 is now available. I'm in the process of testing it. Seems pretty solid, but I can't find out what the new features are.

http://stellarium.org/

Ian
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Re: Stellarium

Postby Grahame Gardner » Wed Aug 25, 2010 3:01 pm

Well, it has been some months in the making, but my Stellarium landscape for Callanish is finally up and working well. I've been wanting to do this one ever since I saw the major southern lunar standstill there in 2006, and I managed to photograph a panorama on a visit there earlier this year. The view is from the end of the avenue, which is the best position for observing the standstill moon. The moon rises from the 'thighs' of the 'Sleeping Beauty' mountain, then rolls along the horizon until it appears to set behind the main circle before 're-gleaming' in the centre of the stones a bit later.

Image

Despite doing my best to align it using Ian's suggested method of extrapolating from GPS coordinates, I found that I still had to do a great deal of fiddling 'by eye' to get the standstill moon to do what it's supposed to do. I also had to paint out a car that had inconveniently pulled up in the road beside the circle as I was in the middle of taking the panorama!
This has definitely been the most difficult landscape I've done so far.

You can find it, as usual, on the Stellarium landscapes page.
Grahame
The trouble with having an open mind, of course, is that people will insist on coming along and trying to put things in it - Terry Pratchett.
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Re: Stellarium

Postby Ian Pegler » Wed Aug 25, 2010 7:40 pm

I just tried the trick with the 2006 lunar standstill - wow!!! Amazing stuff.

Well worth the extra effort, well done!

I had to halve the size of the image-file to get it to work on my poor old PC, alas but it works fine now.

Great bit of patching over the car, I can't see the join!

Ian
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Re: Stellarium

Postby Ian Pegler » Wed Sep 08, 2010 11:14 am

Hello Grahame

I noticed from your Stellarium landscape that one of the large stones at Calanais is at bearing 115 degrees.

This is pretty much identical to the bearing of the largest stone at Mitchell's Fold, give or take a degree
or so.

As I mentioned on the forum, this is the rising position of the Sun at Old Halloween (November. 11th).
In 2000 BC it was also the rising position of Orion, although which bit of Orion depends
(I think) on latitude etc. As I also mentioned somewhere, the same sunrise angle (115 degrees) is found on Corndon Hill,
marked by two cairns.

The change from the Julian calendar to the Gregorian corresponds with the change in the date of
Halloween from Nov. 11th to October 31st. This pretty much conserves the angle so that on October 31st this year,
the Sun will rise behind the stone(s) at all 3 sites.

However, due to precession the rising position of Orion has changed, so it no longer works in relation to the
background stars.

Worth a look.

Ian
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Re: Stellarium

Postby Ian Pegler » Mon Sep 27, 2010 1:59 pm

Ah, another fly in the ointment of life...

Cross Quarter days

I was looking at the value of Right Ascension (of date) for the Sun at the Solstices and Equinoxes. It all seems straight forward enough:

Vernal Equinox (March 21st): Right Ascension of the Sun = 00h00m00s
Summer Solstice (June 21st): RA = 6h00m00s
Autumnal Equinox (Sept 21st): RA = 12h00m00s
Winter Solstice (Dec 21st): RA = 18h00m00s

All well and good. The problem comes with the cross quarter days. In theory the values for Right Ascension of the Sun should be:

Samhain: RA = 15h00m00s
Imbolc: RA = 21h00m00s
Beltane: RA = 03h00m00s
Lughnasadh: RA = 09h00m00s

but going by the days on which the feasts are celebrated it doesn't quite work. Beltane is celebrated May 1st and the value of Right Ascension of the Sun is 2h30m or thereabouts. It seems that the feast-days always precede the theoretical cross-quarter days by at least a day, sometimes nine days.

It does make a noticeable difference under Stellarium as to the position of sunrise. Also, since Stellarium switches calendars automatically, you will need to rely on the Right Ascension of the Sun if you run simulations for further back in time, such as the Bronze Age.

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Re: Stellarium

Postby Grahame Gardner » Sat Oct 02, 2010 5:03 pm

Hey, that works pretty well, Ian. I wouldn't have expected it to be that good as the site is so much further south by comparison.

I've just uploaded my latest, a hi-res landscape of Machrie Moor 5 on the isle of Arran:

Image

A bit of a rush to get this one, as I was worried that I wouldn't have enough time to get back to Brodick for the last ferry, so I just took a compass bearing of East, took the panorama, and legged it back to the car.

More information on my blog, and the landscape can be found, as usual, on the Stellarium landscapes page. Be warned - it's an 8MB file, this one (but it looks great). A low-res version is also available, in case anyone's graphic card is groaning under the strain (like Ian's machine!)... PM or email me if you want the smaller file.
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Re: Stellarium

Postby Grahame Gardner » Sun Oct 03, 2010 1:30 pm

note by I.P. I deleted my post, to which this refers - because of a slight error

Pretty neat indeed, Ian. I'll have to try that with my Callanish landscape when I get a minute.
How did you do it as a matter of interest - did you mask the night landscapes apart from the moon in each shot, then overlay them on a daytime shot? Or is there a simpler way to do it?
Grahame
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Re: Stellarium

Postby Ian Pegler » Sun Oct 03, 2010 2:03 pm

Hi Grahame

It is a bit simpler than that.

First, with Stellarium you should simplify the display - i.e. get rid of anything you don't need, like Azimuth grids, labels etc. You can get rid of the stars by taking the Absolute Scale down to zero.

You freeze time at the appropriate moment and figure out suitable regular time-intervals at which to take your screen shots. Save the screenshots to a suitable folder. In my example the Moons are an hour apart.

You open the first screenshot in Gimp. Then open the second one in a new window, copy the contents to the clipboard and close it down. Then go back to the first image and do a Edit -> Paste as -> New Layer. Using this method you add all the other images as new layers on top of the previous one(s) so the last one will be on the top.

Starting with the most recent (top) layer you do Layer -> Transparency -> Color to Alpha and change the "from color to alpha" to BLACK (html notation = 000000) and hit OK. You should now be able to see two Moons (or whatever) in your image. You then want to go down a layer, so do Layer -> Stack -> Select Next layer and change the "from color to alpha" to black again. Repeat this, going down the layers until you can see all the Moons (or whatever).

When you're finished do Image -> Flatten Image and crop as appropriate.

Hope this helps.

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Re: Stellarium

Postby Ian Pegler » Sun Oct 03, 2010 8:40 pm

Also, File -> Open as Layers allows you to open all the screenshots as separate layers of the same image (select them all using CTRL + click or SHIFT + click). Saves a lot of Copying and pasting.

It doesn't work so well for the Sun - you need to get rid of the atmosphere within Stellarium.

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Re: Stellarium

Postby Ian Pegler » Tue Oct 05, 2010 10:12 am

As an example, here is another "multiple exposure". This is from Lan Fawr Hill, looking back towards Corndon Hill, Beltane sunrise (Right Ascension of the Sun = 3h00m00s), 2500 BCE.

CTRL + click to see the full-size image:

Image

For this shot I only used atmosphere for the bottom layer shot, which was taken before sunrise. For all the other layers I used screenshots taken with no atmosphere. I used the transparency trick for all layers except the bottom one. The shots were taken 20 mins apart because I zoomed in more.

The Sun would have appeared to climb the hiil because the glare makes the Sun appear bigger. To appreciate the effect you need to run the simulation with the atmosphere turned on.

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Re: Stellarium

Postby Ian Pegler » Sat Oct 09, 2010 7:31 am

Stellarium for iPhone !!!

I just came across the following on the Stellarium forum...

Stellarium for iPhone is available in AppStore! Take it at itms://itunes.apple.com/us/app/stellari ... 24365?mt=8


It's free and apparently it can show you what's in the sky wherever you point the iPhone, similar to some commercial apps.

Worth a look.

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Winter Solstice eclipse.

Postby Ian Pegler » Wed Oct 13, 2010 7:25 am

There will be a total lunar eclipse at the Winter Solstice this year (2010).

You should be able to use Stellarium to find out whether or not it will be visible where you are.

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Re: Winter Solstice eclipse.

Postby Grahame Gardner » Wed Oct 13, 2010 7:37 am

Ian Pegler wrote:You should be able to use Stellarium to find out whether or not it will be visible where you are.

Or alternatively, you could use the NASA lunar eclipse calculator.
Grahame
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Re: Winter Solstice eclipse.

Postby Ian Pegler » Wed Oct 13, 2010 9:46 am

Grahame Gardner wrote:
Ian Pegler wrote:You should be able to use Stellarium to find out whether or not it will be visible where you are.

Or alternatively, you could use the NASA lunar eclipse calculator.


Well judging by Stellarium we probably won't be seeing very much in the U.K. It happens around 7:48am just as the Sun is coming up.

Ian.
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Re: Stellarium

Postby Grahame Gardner » Fri May 06, 2011 10:30 am

Here's an interesting topic on Flickr discussing how to produce an equirectangular panorama using Hugin and a few other tools, that can then be used in Stellarium.
I've used one or two landscapes made with this technique and they are useful where it is important to show the ground texture (e.g. roads or tiled surfaces). Not too big an issue for stone circles with grass centres, but I think it's worth having a look.
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