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Angle of crab pulsar to the ecliptic

  1. Dec 22, 2011 #1
    Hi there

    Can any1 tell me, what is the angle that the crab pulsar makes to the ecliptic? - (I am trying to make calculations that require knowledge of the radial velocity between the Earth and Crab)

  2. jcsd
  3. Dec 22, 2011 #2
    It should be easy to discover online:
    The celestial coordinates of the Crab Nebula (right ascension, declination)
    How to change celestial coordinates from equatorial to ecliptic

    I don't feel like posting Celestial Coordinates 101 at this time -- it should be easy to discover in places like Wikipedia.
  4. Dec 22, 2011 #3
    just a related question.... can any1 tell me where I might find a very precise value for the period/frequency of the Crab pulsar? I have looked at the Wikipedia page which is clearly not kosher and his given a period of 33.08471603 miliseconds... the source that is referenced with this value is linked below :


    only problem is this source only gives a value of 0.033085 seconds ..... so it is not clear to me how the wikipedia page is justified in giving the value to so many more significant figures.....

    To clarify, my query is - where might I find a reliable and accurate value for the period of the crab?
  5. Dec 23, 2011 #4
    Sorry if I seemed snotty earlier about posting Celestial Coordinates 101.

    But I found what you were asking about. Start at the SIMBAD Astronomical Database and go to "basic search". Searching for "crab pulsar" reveals one entry: SIMBAD's Crab-pulsar page

    It has that pulsar's coordinates, though not its period. I had to search through the "External archives" links, and the one that gave its period was PSR B0531+21, in the third row and fourth column.
  6. Dec 28, 2011 #5
    another follow up question if I may... !

    I have been given data recorded from the Canary islands and from this data a certain frequency for the crab can be calculated - call this the observed frequency.. this will be different from the intrinsic frequency of the crab because of the radial velocity between the observer (at the Canary islands) and the crab...

    so from the difference of the observed frequency and intrinsic frequency, I was then able to calculate this radial velocity by using the electromagnetic doppler equation and I found this equal to about 20.4km/s...

    now, making the approximation that the crab pulsar lies on the ecliptic (in fact it lies about 1.5 degrees off the ecliptic) and also making the approximation that the only radial velocity contribution is from the orbital motion of the Earth about the sun (ie neglect the Earth's rotational motion), we can say that the maximum radial velocity will be approximately 30km/s - that is the Earth's tangential velocity will be equal to its angular velocity omega multiplies by the radius of the circle of its orbit - so omega=(2*pi)/(365*24*60*60)rads/second and radius=1AU=1.5*10^11meters and so omega*radius is approximately 30km/s....

    What I am having trouble doing (and using the approximations I calculated) is figuring out what time of year it must have been such that the radial velocity was equal to about 20.4km/s..
    I think that it must be down to the right ascension coordinate.. for the crab RA=05h 34min...
    how can I figure out from this RA value and the radial velocity value, what time of year it must have been... ?
  7. Dec 28, 2011 #6
    to add to my last post...

    What I don't know is how to figure what time of year will create a given radial velocity to the crab,
    I think what would help figure this out is if I knew what would be the RA of an object such that the radial velocity (only due to Earth's orbit) would be zero at both the summer and winter solstice..

    And in a similar vain, what be the RA of an object such that the radial velocity would be zero at the spring and autumn equinox...?
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