2007 Autumnal Geosat Flare Season

From: Jeff Umbarger (jumbarger2000@yahoo.com)
Date: Wed Sep 26 2007 - 00:17:30 EDT

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    Hey Everyone,
         The 2007 Autumnal Geosat Flare season has already
    started (actually, it is more than half over!) and now
    it is a purely Northern Hemisphere event. Over the
    next few nights you will have a chance to see
    spectacular flaring of geostationary satellites
    (geosats) at certain points of the night. These flares
    will rival the brighter stars in the sky and last for
    several minutes (not seconds like Iridium flares),
    lighting up and then dimming down from the east to the
    west along a thin line near the celestial equator –
    like a string of diamonds slowly lit by flashlight.
    And occasionally, you may catch a stunning set of 2 or
    more very compact geosats flaring all at once (like
    the XM satellites for my location). And at nearly 6
    earth radii away you will know that you are viewing
    the most distant manmade objects possible without the
    need for binoculars or a telescope (although these
    instruments will help you see the dimmer geosats of
    which there are many more).
         The last couple of years I provided star charts;
    this year it is tables! These tables will tell an
    observer, based on their latitude and date where and
    when to look in the night sky to maximize their chance
    of seeing a flaring geosat. In particular, the table
    will, for each latitude and date, define two times in
    the night – one when geosat flaring ends in the
    evening hours because of the earth’s shadow covering
    up the observing point and the other time in the early
    morning when the earth’s shadow uncovers the observing
    point. This makes the middle of the night the worse
    time to look for flaring geosats and the time after
    sunset and before sunrise the best time. As the dates
    progress from late-September to mid-October, these two
    times in the table, for each latitude and date,
    converge towards each other on local midnight and
    afford the viewer a much greater (higher elevation)
    opportunity to see flaring geosats. This makes this
    process more and more exciting with each passing
    night. (And the full moon will not be problem for the
    mid-to-high latitude observers this Fall!) 
         Kevin Fetter has helped me greatly by hosting the
    necessary tables on his website at:
         At the website there is a very in-depth
    explanation and example of how to use the tables.
    However, I'll give a "quick" explanation as to how
    they work for those more familiar with this hobby.
         In the webpage above, find the table that applies
    to your latitude and the date you want to observe. The
    PD Dec. column (by your latitude) and the PDRA row (by
    the date) define the point (PD means Purple Dot) where
    you want to always be looking, throughout the night.
    You will start observing at the PD Rise Time (PDRT) in
    your east (shortly after sunset) and stop when the
    first of two times in the body of the table is reached
    for your latitude and date. This is when flaring at
    the PD stops and the PD is eclipsed. It re-starts at
    the second time in the table (as the PD becomes
    uneclipsed) and continues until the PD sets in your
    west (shortly before sunrise). You will always look
    along your PD Dec. line from the eastern to the
    western horizon since this is the only place you will
    see geosats.
         The times given for PDRT and the two times in the
    body of the table are assuming "Local Midnight" is at
    12:00AM each night. You will have to adjust the PDRT
    and the two times in the table for each date by
    determining your *actual* local midnight time. This is
    the time that is halfway between sunset and sunrise,
    based on your local timezone. If this time is after
    12:00am, you will have to add it to the PDRT and the
    two eclipse times for that date.
         Here's an example of how to use the tables for me
    at latitude +33.06946N and on October 5. On that date
    for my location the halfway point between sunset and
    sunrise is 1:16am Central Daylight Time (CDT). I got
    this information from my Heavens-Above webpage under
    the "Sun" link, at the bottom called "Minimum
    Altitude". (BTW, this time changes almost every night
    so it must be looked up for each observing night for
    me.) I find the table (there are 12 of them) that
    applies for latitude 33 and date Oct 5 (4th table
    down). The point I need to watch (the PD) is at RA:
    0:45:28 (the PDRA under the date) and at Dec.:
    -5.39deg (the PD Dec. next to the latitude 33). This
    point rises at 6:12pm Local Midnight Time (PDRT next
    to latitude 33), is eclipsed at 6:33pm Local Midnight
    Time, and is uneclipsed at 5:26am Local Midnight Time.
    I then *add* 1hr16min to those 3 times and get a
    corrected time of PDRT=7:28pm CDT, PD Eclipse
    Time=7:49pm CDT, and a PD Uneclipse Time=6:42am CDT.
    This means, as I watch the PD rise from 7:28pm CDT to
    7:49pm CDT, the PD is uneclipsed and I stand the
    greatest chance of seeing a geosat flare. Then from
    7:49pm CDT until 6:42am CDT the PD is eclipsed and
    there shouldn't be any geosats flaring *at* the PD.
    Then after 6:42am CDT I should be able to start seeing
    flaring at the PD until it sets in the west. This, at
    least intially, is not a lot of time to watch for
    geosats. But if you look right across increasing
    dates, you will see the eclipse (evening) and
    uneclipse (early morning) times begin to converge on
    local midnight, affording more time to see flaring
    geosats. On October 16 the earths shadow pulls off the
    geosat orbit and the RD uneclipsed *all* night!
         Additional information:
    1.) The Date at the top of each table is based on 0
    (zero) UT. As the day progresses, the sun moves lower
    in declination so that for those around +/-180
    East/West longitude, the information may be more
    2.) In the evening, even after you PD is eclipsed
    *continue* to look west of the PD along the PD Dec.
    line. You will see *most* of the geosats begin flaring
    out here.
    3.) In the table, the term "NVAN" means Not Visible
    All Night, meaning the PD stays under the earth's
    shadow all night (not good for geosat flaring!).
    4.) In the table, the term "VAN" means Visible All
    Night, meaning the PD is not eclipsed all night by the
    earth's shadow. This will start on October 16 and
    continue until next February!.
    5.) If you want to continue looking for geosats after
    the season officially ends (on October 16), just keep
    looking at your PD Dec. and a PDRA that is exactly
    opposite the sun's RA.
         Please let me know if you have any questions and
    please tell me about any observations or lack there of
    you've made. I would like to thank Kevin Fetter for
    hosting my files, Greg Roberts for throwing out my
    earlier equations with incredible observations last
    April, ushering this new data, and Rod Austin for
    confirming that Greg was correct! M
         The first thing you must know is where to look.
    For a given latitude, you always look along the same
    *declination* (Dec.) each night from the eastern
    horizon to the western horizon. The right ascension
    (RA) you will look at will be at the RA that is
    exactly opposite the sun's RA (add or subtract 12
    hours from the sun's RA). So each night for a given
    observer, the declination doesn't change but the RA
    does. I call the this point the "Purple Dot" or PD and
    in the tables below you will see the terms "PD Dec."
    for Purple Dot Declination and "PDRA" for Purple Dot
    Right Ascension. When a geosat is at this point in
    your sky *and* this area is *not* eclipsed by the
    earth's shadow, there is the maximum chance of the
    geosat flaring.
         The second thing you must know is when, each
    night, to look at the Purple Dot (PD). These times are
    driven by when the earth's shadow eclipses the PD in
    the evening ("Eclipse Starts") and when the earth's
    shadow uneclipses the PD in the early morning
    ("Eclipse Ends"). Even though the PD rises, crosses
    the local meridian, and then sets at the same time
    each night (relative to "Local Midnight" - more about
    this later) the eclipse times change greatly each
    night. How do these times change? On September 23rd
    almost everyone (except those on the equator) had no
    chance to see their PD uneclipsed in their night sky.
    In other words, the PD was "Not Visible All Night" -
    NVAN - a term I use in the tables. Then at some date
    later than September 23 (for the Northern Hemisphere)
    the PD will rise in the east in the evening uneclipsed
    and move some distance west before being eclipsed by
    the earth's shadow, which catches it from the east. It
    will stay eclipsed throughout the middle of the night
    until some time in the early morning, before it sets,
    when it will become uneclipsed by the shadow racing
    off faster to the west. During very middle of the
    night you should not see any flaring geosats *at* the
    PD. Throughout the following nights, the eclipse and
    un-eclipse times converge on Local Midnight - giving
    the observer greater and greater opportunities to see
    flaring geosats at their PD. Then on October 16, the
    PD will be "Visible All Night" - VAN - for everyone.
        If you go to this webpage, you will see 12 tables,
    each 72 columns in width. There are 6 tables for
    Latitudes 0 - +39N and 6 tables for Latitude +40N -
    +80N. Choose your 6 tables based on your latitude.
    Each latitude has 6 tables for 6 different sets of
    dates - 4 days in length each. Across the top of each
    table is the date *at 0.0UT*, the sun's declination
    for each date at 0 UT, and the Purple Dot's Right
    Ascension (PDRA) for each date. Down the left column
    is the observer's latitude, the Purple Dot Rise Time
    (PDRT), and the Purple Dot Declination (PD Dec.). The
    body of the table is made up of, for each latitude and
    date, the eclipse start and end times *based on
    Standard Local Midnight* which is always 12:00am. Your
    actual Local Midnight time is the point halfway
    through the night between sunset and sunrise and is
    based on your timezone and longitudinal offset. You
    can get this from your Heavens-Above site by clicking
    on the "Sun" link in your main page and reading the
    "Minimum Altitude" time at the bottom of the page. THE
    5 my actual local midnight time will be 1:16am Central
    Daylight Time. I will then *add* 1 hour 16 minutes to
    PDRT for my latitude and the two times in the table
    for my latitude on October 5. On Oct 7, the my actual
    local midnight time changes to 1:15am CDT, so I will
    add 1 hour and 15 minutes to my PDRT and the two times
    under 7-Oct.
         So here is an example on how to use the tables
    for myself on October 5. First I would go to the
    webpage above and find the table has my latitude down
    the left side and the date October 5 across the top.
    In this case it's the 4th table down from the top of
    the page. I would next find my latitude (I live at
    +33.06946N) at 33. The next number over is the PDRT or
    the time at which my PD rises. It's 6:12pm Standard
    Local Midnight time. It will *always* be 6:12pm *every
    day of the year*. Then I will apply my offset,
    describe above, by adding 1hr 16min, to get 7:28pm
    Central Daylight Time. This is the actual time, on my
    watch, that PD will rise uneclipsed. The next number
    over is the PD Dec., so I will always track this
    declination (-5.39 deg.) all the way from the eastern
    to the western horizon. The PD will move right down
    this declination each night for me. Then I track over
    to the 5-Oct column and the two numbers there, 6:33PM
    and 5:26AM are the times on Oct 5 that I see my PD
    first get eclipsed and then later uneclipsed. I
    convert these two times to my actual time by adding
    1hr 16min to each of them to get 7:49pm CDT and 6:42am
    CDT. At the top of the column by the Oct 5 data is the
    PDRA which is 0HR 45MIN 28SEC. So what this all means
    is that on Oct 5, on a star chart I will mark the
    location (with a purple marker!) RA: 0:45:28 and Dec.:
    -5.39deg. I will then face my eastern horizon and at
    7:28pm CDT this point in the starfield will rise
    *un-eclipsed* with opportunity as each geosat drifts
    left in front of that point to have that geosat flare.
    At 7:49pm CDT, the PD will be eclipsed from the east,
    so I will no longer see flaring at the PD until 6:42am
    CDT the next morning when geosats, to my west, begin
    flaring at the PD. As the days after Oct 5 go by, the
    7:49pm time moves toward local midnight and so does
    the 6:42am time - giving more and more dark night time
    to see optimally flaring geosats.
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