(meteorobs) A real Earth-grazer

[stange]

Esko,

Other than by calculation from altitude triangulation Esko, do you know any 
way in which an earth grazer (might) be identified from a single photograph 
from one site?

 YCSentinel


----- Original Message ----- 
From: "Esko Lyytinen" <esko.lyytinen at jippii.fi>
To: <meteorobs at meteorobs.org>
Sent: 2008/09/24 13:32
Subject: (meteorobs) A real Earth-grazer


>
> Hi,
>
> An Earth grazing meteor(oid) was captured here in Finland by two
> fireball cameras in 2008 Sept. 22 at 01.14 UT.
> This was not especially bright, only near the fireball-limit, as seen
> almost below in the Jari's images and video, see below.
>
> It was captured by Jari Tuukkanen with an all sky camera and
> UFOC-program ( V2.21 )and by Timo Kantola with a wide field camera and
> SkyPatrol4 program. We received only one eyewitneess report to Ursa.
> This was observable in either of the cameras for about 15 seconds.
>
> This was already bright at the start of Jari's capture and was prbably
> prevented from earlier capturing because of a too slow angular velocity
> earlier, for the UFO.program definitions. Also the end of capturing was
> probably from this reason. Timo had the start of capturing earlier, but
> in this the still earlier capturing was probably prevented by clouds low
> in the sky. In Timos image it went outside the field after about ten
> seconds of visibility.
>
> The data of these two cameras allowed a very accurate trajectory
> derivation (with also the Earth gravity effect applied during the
> flight. It appears that the trajectory had its most low point when
> visible in Timo's image and close to the start of Jari's video at the
> height of 87.3 km, from sea level. The derived velocity then was 17.89 
> km/s
> The trajectory fitting ws done into about 130 half-frame (automatic)
> UFO-position measurement points, these treated as mutually timed
> observations. The SkyPatrol image was measured for 12 (non timed points)
> along the track.
>
> At that height the atmospheric density is very slow. An attempt was made
> to derive the deceleration, with the assumtion of it being constant
> during this.
> A value of (as small as) 1 m/s^2 was achieved, but this is probably too
> small a value to trust as distinct from zero, (or from any other
> smallish value).
> In any case it appears quite sure that the meteoroid went back into the
> interplanetary space, with almost unaltered velocity relative to the 
> Earth.
> If that deceleration value were correct the meteoroid would have been as
> big as about 200 kilograms ( if chondritic density). This is not
> reliable however. So it is very difficult to get any reliable mass value
> for this. This height may be aroud the typical beginning height of this
> slow meteors, so the brightness probably does not give anything to tell
> this.
> This was also well visible in my forward scatter radio data, which may
> not be very typical for this low meteors/fireballs, according to my
> experience.
> In this, first an overdense reflection appears, then the specular or
> head echo and it continues as an overdense for some time. The visible
> band is only 100Hz wide and the head echo would pass over this in about
> a second, so this deos not allow the measurement of  the frequncy drift
> value here. Probabaly a more wide visible channel would have given
> something on this.
>
> In the video, a weak trail is more or less visible.
> You can see the mp4 form video of Jari at:
> http://www.horseheadobservatory.com/grazer/
>
> Timo's image can bee seen at:
> http://img91.imageshack.us/img91/7792/200809220114utov3.png
> Here it goes from lowere left to upper right.
>
> The solar system orbit before the encounter (as derived with Marco
> Langbroek's Excel sheet) has
>
> a=2.67
> q=0.869
> e=0.674
> peri=48.10
> node=359.291
> i=8.31
> The geocentric radiant is
> 344.18 , -29.96 (angular values J2000.0)
> Vinf 17.9km/s and Vgeo 14.2 km/s
>
> Esko Lyytinen
> Jari Tuukkanen
> Timo Kantola
>
> _______________________________________________
> Mailing list meteorobs: meteorobs at meteorobs.org
> To UNSUBSCRIBE, email: owner-meteorobs at meteorobs.org
> http://lists.meteorobs.org/mailman/listinfo/meteorobs