October 31th, 2007 Dual Iridium Flare

10/31/2007 Dual Iridium Flare Minnesota River Valley Wildlife Preserve, Wilkie Unit, NFS

October 31th, 2007 19:43:23/19:43:45 CDT(UTC-5) Iridium 30/95

Daniel Crawford who does flare predictions up to a month ahead of time sent me an e-mail on 10/6 alerting me to another opportunity for dual flares on Halloween. I have always wanted to take a shot below a bridge of the flares between the bridge, plotting a centerline between the two flares I came up with a centerline along Hwy 169 thru the Metro Twin Cities. Selecting the Minnesota River Crossing on Hwy 169, plugging in the numbers I came up with the following use updated elements.

Flare Details

Iridium flares / Orbitron 3.71 / www.stoff.pl
Location : Minnesota River Valley National Wildlife Preserve(NFS) Hwy 169 Bridge(93.4035° W, 44.7921° N)
Time zone : UTC -5:00
Search period : 2007-10-31 19:43:00
2007-10-31 19:44:00
Conditions : Maximum sun elevation = -5 deg
Minimum sat elevation = 10 deg
Illumination required
Minimum magnitude = 3.0

Time Sat Azm Elv Range A D Mag S.Azm S.Elv
—————————————————————-
2007-10-31 19:43:23 30 22.1 43.7 1074 L A -6.2 267.7 -18.1
2007-10-31 19:43:45 95 ? 22.7 44.4 925 L A -6.1 267.8 -18.2
Astronomical Twilight begins at 19:42 – it will be dark
Moon Rise is at 11:02PM 58% illuminated.

Targeting

As I have said I wanted to always capture a flare between the openings in a bridge, in this case the North and Southbound lanes of Hwy 169 over the Minnesota River Valley. Given the centerline this was a good choice about spot on the centerline.

Planning

I was familier with the site (Wilkie Valley Unit – Minnesota River Valley National Wildlife Preserve (NFS)) having been thier several times checking out the largest Blue Heron population in the State with over 600 nests. I calculated the centerline several times, eachtime it ran near Hwy 169 thru the Metro. I wanted to light the underside of the bridge with high intesity lighting (green, red, blue) but, alas I have no high powered strobes/lighting and colored filters. The side of the bridge is illuminated by the street lights. I checked earlier and the street lights are positioned on the outside of the Northbound and Southbound lanes of the highway which means I would take my shot between the North and Southbound lanes with the sides of the bridge lit by the street lights along with some decent light pollution overhead. I checked the rules, while most parks community/county/regional/federal, etc close at sunset, this particular area has a Minnesota River Boat Launch which is available 24×7 (just to 365 days a year). I took the shots from the boat landing gravel parking lot, otherwise the rest of the refuge is off-limits after dark.

Execution

The Search

I had previously had the location in mind once the centerline overlaid it. I reconed the area and spoke to the MN Vly NWR regarding availabillity of the boat launch area prior to the event.

Composition

The bridge on the South side is curved on the South Side it runs NW to SE rather than North to South. Given the fact that the flare would be 22 degrees North as well as 44 degrees above horizon this would create a challenge. I had vowed just two days prior that I would never do a wide angle Iridium Flare shot again. Due to the angle of the bridges I composed the shot with both the bridge in mind and the flare in mind. In hindsite I should not have shot so wide and just focused on one side of the bridge as a forground object. I was not concerned with any other objects, stars, constallations, comets, etc.

Observations

The flares were closer than predicted, at maximum brightness the flares did not have enough speration given the focal length (I used too wide of angle so it looks like one flare, if you look at the full size crop you can see both satellites).

The Photos

Click on photos to see large versions

Setting up the shot I had to get an image of the comet 17P/Holmes, the fuzzball in the upper left.

The composition was a portrait. It’s difficult to find targets tall enough, far away enough, to be in focus given the height of the flares when they occur and depth of field (focus). Due to the wide angle the flare is the white slant in the middle of the shot. (click on link for larger image)

Slightly Cropped

Crop of Flare

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