Jump to content

Banner.jpg.b89429c566825f6ab32bcafbada449c9.jpg

Calculating the position of the galaxy center on night sky.


Recommended Posts

Hello,

I want to repeat Mr. Shapley's computation of the galaxy center position and distance from Earth. I gathered right ascentions and declination of almost all known global clusters in Milky Way and their distances from the Earth, as Shapley did one hundred years ago (1918). But what should I do now? I can not find any information how did he proceed it. Could you give me an advice or share a source in which it is described?

Peace

Quantum

Link to comment
Share on other sites

With RA/Dec coordinates and distances, a simple, flawed approach would be to convert to Cartesian coordinates and average.

Take for example, a cube:

blob.png.34759fc6553882f01f70de54516ca875.png

I propose that there are globular clusters at each vertex, A-H. The observer is at A.

 

https://en.wikipedia.org/wiki/Spherical_coordinate_system#Cartesian_coordinates

The RA/Dec and distance I have inferred in the following table, using the symbols for azimuth and elevation from the link above:

blob.png.6733a32a90a173070581943dc499fe76.png

Note:

  • RA of B from A is 0 deg and C from A is 90 deg.
  • Dec of B from A is 0 deg and E from A is 90 deg.
  • θ measures elevation not inclination, so refer to the "switch" mentioned in the link above.

 

I perform a coordinate transformation and average:

blob.png.7048760e1fb78a76639948ec2fe94bd9.png

The average is the proposed "center" and it's cartesian coordinates can be converted back to RA/Dec and distance.

 

A different approach here:

http://adsabs.harvard.edu/full/1962AJ.....67..769F

 

Link to comment
Share on other sites

19 hours ago, Quantum said:

 

 But what should I do now? I can not find any information how did he proceed it. Could you give me an advice or share a source in which it is described?

Peace

Quantum

I have no idea what Shapley actually did. Do you know which underlying assumptions he made about the likely distribution of globular clusters?

Link to comment
Share on other sites

In "Man Discovers the Galaxies", by Berendzen, Hart & Seeley, there's a couple of sections (p26, p42) which go into detail of Shapley's work on globulars.

Basically the distribution was based on the recorded Galactic coordinates of the known clusters (about 120) and the distances by using Cepheid and RR Lyrae variable stars. He also "approximated" the distance of the more distant globulars based on their angular dimensions (p89). 

Hope this helps.

 

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.