[Closed] Any astronomy experts in?

Take a screen grab of something like stellarium?

As a potential idea, could you take a photo of the night sky at a location meaningful to you (Ireland) and get it printed to the same size as your desired lamp shade. Lay the photo over the shade and poke holes in the shade, through the photo to recreate the stars?

I need the numbers. Its going into a CNC router.

This claims to be Cartesian but not in a format I can grasp http://www.astronexus.com/hyg can anyone explain the x,y,z bit in terms of a 2D view looking up?

have you thought about using a planisphere?
[img] [/img]

large ones are around £10

EDIT but then I found this which has the map section of a DIY planisphere although getting the section of night sky that you want may be tricky unless you complete it

can anyone explain the x,y,z

can you post a couple of examples?

can you post a couple of examples?

This is what it says:

[i]X,Y,Z: The Cartesian coordinates of the star, in a system based on the equatorial coordinates as seen from Earth. +X is in the direction of the vernal equinox (at epoch 2000), +Z towards the north celestial pole, and +Y in the direction of R.A. 6 hours, declination 0 degrees.[/i]

A few examples (Name, X, Y, Z)
Betelgeuse 3.189296 151.364387 19.682142
Vega 0.960565 -5.908009 4.809731
Babcock's star 53443.38342 -18369.41072 82500.72435

Hour circle
[img] [/img]

Right ascension is the angular distance measured eastward along the celestial equator from the vernal equinox to the hour circle of the point in question
declination is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. Declination's angle is measured north or south of the celestial equator, along the hour circle passing through the point in question

Convert Right Ascension to degrees
A = (hours * 15) + (minutes * 0.25) + (seconds * 0.004166)
As declination is already measured in degrees, but can range from -90 to +90 so the absolute value is taken
B = ( ABS(Dec_degrees) + (Dec_minutes / 60) + (Dec_seconds / 3600)) * SIGN(Dec_Degrees)
C is the distance to the star in light years
Now

X = (C * cos(B)) * cos(A)
Y = (C * cos(B)) * sin(A)
Z = C * sin(B)

Have fun

nickjb - Member
I need the numbers. Its going into a CNC router.

Usually you can convert an image into a toolpath.

Bigbutslimmerblokee- thanks for that clear explanation. My head has just exploded!

Was out looking at the stars last night. I'd just like to know the names of a few of them.

Usually you can convert an image into a toolpath.

Yeah, but I want to normalise the hole sizes and make them perfectly round so it doesn't quite work this time.

Looks like I might just be tracing the jpg in cad. Shouldn't take too long. Just seems a shame as the jpg I have was generated by a list of numbers which is the list I want. Just can't seem to get it in that format.

I'd just like to know the names of a few of them.

The easy answers are
- Collins Guide To Stars And Planets - has diagrams of the constellations, names and descriptions of the stars and (what I really like) the mythological background to the constellations (Algol in Perseus is binary star which varies in brightness over about 5 days, it represents the Medusa's eye glaring at the seated figure of Cassiopea on the other side of the sky - think near the end of Clash of the Titans)
- a Planisphere, sometimes included with Collins Guide. A couple of bits of plastic stuck together to give you the nght sky at any time on any date
- Google SkyMap, just point your phone at the sky and it'll tell you what you're looking at, includes planets which the other can't.

With the book or the planishere, invest another £5 or so for a torch which has a red filter as you can read with it but not affect your dark adapted eye

You might also want to have a look at the Heavens Above app which has satellite info as well, including ISS

EDIT Collins Guide appears to be out of print but is available used from Amazon for >£3 including postage. I would grab one if you're in any way interested

Nick, given that the z coordinate is a function of the distance from here so can be ignored, can't you work with the x,y coordinates you have?

Nick, given that the z coordinate is a function of the distance from here so can be ignored, can't you work with the x,y coordinates you have?

Can't see how. If I'm at a specific point on earth then looking straight up I'm looking at a 2D projection onto an oblique plane slicing through those X,y,z coordinates

Any astronomy experts in?

What does it matter, this place is full of "experts" who will gladly offer their advice 😆

Or, according to flat earthers, you're looking at a dome with points of light painted onto a 2D surface, so if you take a jpg of a star chart or planisphere, overlay it with a grid, you'll create a 2D map which, while maybe not accurate enough to pilot the Enterprise, should do for your needs. I'd have thought that would be do-able by using your own coordinate system, say Polaris as the Origin, x axis spreading EW and y axis NS. Or maybe move Polaris to be further up the y axis as it isn't directly overhead

Your problem is converting a part of a sphere to a 2D plane if I understand correctly. So you just need to use a bit of trigonometry to convert from the XYZ to an XY plane.

That's already been done on 2D star charts, so as far as I can see it's a matter of taking an existing chart, resizing it as appropriate and copying it. It only gets complicated if he wants to display a part of the sky for which there isn't a chart. A planisphere might be on the small size to map, but Collins and Phillips Guides have month by month maps for around 50 deg N which would provide the detail, I'd have thought

Your problem is converting a part of a sphere to a 2D plane if I understand correctly. So you just need to use a bit of trigonometry to convert from the XYZ to an XY plane.

Yep, that's the gist of it. The issue is that the existing X, Y, Z data is in a not with respect a fixed plane and my new XY plane is at an oblique angle to that data, so yes it "just" trigonometry, but rather complicated.

I was hoping as its pretty trivial to get a 2D star chart from many apps and websites I could get hold of that raw 2D coordinate data from somewhere but I can't seem to find it. Or to use the algorithm that the apps use to generate my own chart, but again that is proving tricky.

I'm currently tracing a jpg of a start chart I generated. Slow and dull but getting there. Not an elegant solution but a working one 🙂

Thanks BBSB.

We are often looking out for satellites and ISS, so will have a look at your suggestions.

Sky at Night magazine has a two page centre fold map of the night sky every month. Pretty much covers everything you'll be able to see in the sky if it wasn't for the clouds and my neighbours with their 'Heathrow runway' security lights. 👿

Yep, that's the gist of it. The issue is that the existing X, Y, Z data is in a not with respect a fixed plane and my new XY plane is at an oblique angle to that data, so yes it "just" trigonometry, but rather complicated.

This is true.

Do it one axis at a time in an excel sheet, and you'll get somewhere. Check your calcs, then check everything comes out looking OK.

Do it when you're not tired.

Was out looking at the stars last night. I'd just like to know the names of a few of them.

There’s an app for that...
https://en.m.wikipedia.org/wiki/Star_Walk
The classic and most easily identified constellations are really all you need, Gemini and Cancer are basically two shared stars, the rest aren’t that well defined, whereas Ursa Major, Ursa Minor, Cassiopeia, Cygnus, Auriga, Orion, Canis Major and Taurus are all instantly recognisable and visible in the northern night sky during most of the year, although Orion is really a winter constellation. Some of their brighter stars are fairly well known; Sirius, Betelgeuse, Capella, Aldebaran, Mintaka, others less so, but it’s the shapes that are important, we do have two Northern Cross constellations, but neither are known by that name, one is Cygnus, the Swan, the other Auriga, The Charioteer, but both are pretty much perfect cross formations.