Hi Allen, > Secondary question: has anyone tried to see any except solar and lunar > Iridum flares/blinks? Venus, Jupiter, Sirus, I-flares for example? About six months ago I wrote a modified version of IRIDFLAR to search for glints from Venus, Jupiter, Mars, Sirius, Vega, and a few other bright stars, without really thinking through whether they would be visible. Later, after working out the math/optics it became clear that the glints would be of such short duration (and the pointing tolerances so high) that they probably would not be detectable. (Consider how dim a lunar flare is, even from a full moon.) While the planets have the next brightest visual magnitudes after the sun and moon, their ~radiances~ rather than their ~irradiances~ is what matters for this type of optical setup. While Venus can be magnitude -4.5, its angular size (solid angle) is hundreds to a thousand + times larger than that of an Iridium MMA. Thus, the MMA specular reflection only samples a small fraction of Venus as it sweeps the planet. Call it a factor of 1000, which is 7.5 visual magnitudes. If so, a Venus glint would be about magnitude +3. If the planet subtends ~15 arcseconds, then the MMA will sweep across the planet's disk in about 1/30th of a second. Therein lies the problem. Stars, while dimmer, have much higher radiances. Since their angular sizes are less than that of the MMA, you see a complete reflection of the star. Assuming the MMA has 100% reflectivity (it's a little less than that, but close enough), the star glint will be a mirror-image of the star -- i.e. the same magnitude. So a glint from Sirius would still be magnitude -1.4. But the duration of the event would be less than a millisecond due to the satellite's motion. --Rob ----------------------------------------------------------------- Unsubscribe from SeeSat-L by sending a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@lists.satellite.eu.org http://www2.satellite.eu.org/seesat/seesatindex.html
This archive was generated by hypermail 2b29 : Wed Oct 25 2000 - 12:06:34 PDT