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Diameter of star clusters

  1. Aug 5, 2010 #1
    Maybe this is stupid question, but I am not sure how to get the diameter of the star cluster, I assume from the RA and Dec. I googled it and tried to come with a realtion between the RA , Dec and Diameter from Andrea's proposal but couldn't figure the correct answer
    This is all I find (see below please)... but I don't know the distance or the angular size, just RA and Dec from SIMBAD data base
    diameter = 2p × (distance to the cluste) × (clsuter's angular size in degrees)/360°
  2. jcsd
  3. Sep 2, 2010 #2
    hey, i can't quite remember everything, but here goes:

    if u have the magnitude of the cluster u can work out the distance to the cluster. the absoulte magnitude of the cluster will (should) be on simbad.

    the equation for magnitude and distance is:

    u can work out the angular size using the distance u just calculated using:

    however, it should be poss to find out the cluster's angular size from a catalogue.
    If simdbad doesnt have it, use the search tool to search thro all the other cataloguesthat simbad has access too:

    enter the cluster's name or ra and dec and it will give u a list of catalogues which has data on which u can view by selecting them. it will take some time but u prob will be able to find the clusters angular size :) (no gauntees of course!) if u do have enough info to use the formula i would recommend doing it the formula way lol for time purposes

    the eqaution u wrote is based on triganometry, and assuming the cluster is spherical (just like working out the disameter of the moon, but further away) so i would reccommend looking up about working out the diamter of the moon, they have good diagrams to help u visualise the problem and understand it better

    hope this helps

    p.s apologys for the poor spelling!
    Last edited by a moderator: Apr 25, 2017
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