Re: Number of Observable Satellites

From: Bjorn Gimle \(TietoEnator\) (
Date: Thu May 23 2002 - 08:36:58 EDT

  • Next message: Frits Westra: "Re: Number of Observable Satellites"

    > I get this question from time to time:  "how many satellites are there in
    > space"  I know that number is huge and how many one sees is dependant on
    > how sharp ones eyes are, the darkness of the sky, etc., etc.
    The darkness also affects which satellites are sunlit, and unless you live
    in the tropical zone, the length of the twilight period varies considerably
    with latitude, and with seasons.
    Latitude also affects which satellites you can see - which is one objection
    to using fixed sets of "bright" satellites (some are hardly visible outside
    lat 30-40 N/S). Some sun-synchronous objects (98 deg.inclination) that pass
    near noon/midnight are never seen in the tropical zone! Molnyia-type objects
    can be visible at 50-70 degrees S; many rockets from geosynchronous launches
    are only visible in a small band near the equator; others anywhere between
    +-30 degrees (all of those providing the perigee happens to be in the
    twilight zone).
    If you are interested in the number of visible passes, as opposed to number
    of unique objects, I recommend running a prediction program with a magnitude
    file, like SkyMap or QuickSat, or querying HeavensAbove with varying
    magnitude option. At higher latitudes the separation between passes in the
    E-W direction is smaller(also the N-S separation for orbits with visibility
    near their apex), and increases the number of passes of a single object in
    one night.
    The coming week, HA gives me (at +3.5 mag.) 4-8 passes in the evening, 2-5
    in the morning, 10 average/night.
    At +4.5 mag. I get 48 passes/night.
    I can get to +5.0 by changing the HA URL (not on the menu), and get 98
    Moving to lat.+39, the last number increases to 144 at mag +5. (My nights
    are short!)
    For the week ending March 15, they get 78 passes, while I get 206 ! (Easy to
    count - and print condensed - with copy/paste of table into Excel)
    -- (office)                         --
    -- (home) --
    -- COSPAR 5919, MALMA,    59.2576 N, 18.6172 E, 23 m         --
    -- COSPAR 5918, HAMMARBY, 59.2985 N, 18.1045 E, 44 m         --
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