See satellites in broad daylight!!
Iridium flares can be so bright that they are actually visible in daylight, even when the sun is well above the horizon. As keen astronomers know, the planet Venus (Mag. -4) can be seen during the daytime, provided it is not too close to the sun and one knows exactly where to look. A magnitude -8 Iridium flare, which is about 40 times brighter than Venus, is much easier to see, even though it only lasts for no more than a couple of seconds.

Only the very brightest flares can be seen in the daytime, and so they don't occur as frequently as nighttime flares. They are even more sensitive to your position, so it is extremely important to determine your position as accurately as possible. To avoid dissappointment, you should try to get your position to an accuracy of about 2 km, which corresponds to an accuracy in latitude/longitude of approximately 0.02° or 1 arc minute.

For more information, please see the Iridium flare help page or visit the Visual Satellite Observer's Homepage

Interpreting the Predictions
The following is an example of the daytime flare predictions table;

Date	Local Time	Intensity (Mag.)	Flare position		Flare centre		Sun			Satellite
			Elev.	Azimuth	Distance	Mag.	Elev.	Azimuth	From flare
05 Nov	16:03:38	-7.7	81°	118° (SE)	3.2 km (E)	-8.4	6°	238° (SW)	88°	Iridium 36
07 Nov	09:39:14	-7.5	66°	183° (S )	2.9 km (W)	-7.8	19°	145° (SE)	53°	Iridium 73
07 Nov	15:52:34	-8.3	80°	135° (SE)	1.3 km (E)	-8.4	7°	236° (SW)	85°	Iridium 35
08 Nov	09:33:59	-7.4	67°	184° (S )	3.1 km (W)	-7.8	18°	144° (SE)	56°	Iridium 63

We will now explain each of the table columns in turn.

Date

The date on which the flare occurs (in local time). Several flares can occur on the same day.

Time

The exact time when the flare reaches its maximum brightness (in local time).

Intensity

The estimated maximum intensity of the flare in the standard astronomical magnitude scale. This is a logarithmic scale and it is important to note that lower numbers represent brighter flares. The scale is defined such that a magnitude difference of 5 represents an intensity difference of factor 100. Thus a magnitude -7 flare is one hundred times more intense than a magnitude -2 flare. As a comparison, the brightest star in the sky (Sirius) has magnitude -1, the planet Venus (the brightest star-like object) can reach magnitude -5, and the full Moon shines at magnitude -12. Please remember that these magnitude estimates are only approximate, and are affected by errors in the Iridium satellite attitude and position errors of the observer's location. A 10km position error on the ground can easily result in an estimated magnitude error of several magnitudes.

Flare position - Elevation

This is the angle above the horizon, in degrees, at which the flare reaches its maximum intensity.

Flare position - Azimuth

This is the angle measured clockwise around the horizon from true north, at which the flare reaches its maximum intensity. Thus, an azimuth angle of 0° represents north, 90° is east, 180° is south and 270° is west. To make sure you are interpreting the angles correctly, start facing the northern horizon, then rotate clockwise through the azimuth angle about the local vertical axis. Finally, look up from the horizon through the elevation angle.

Flare centre - Distance

The flare centre corresponds to the point on the earth´s surface where the flare is brightest, and NOT the position of the satellite itself. The information is given for people who want to travel to the flare centre to get the best view. The distance columns gives the distance from the observers location, and the approximate direction. Since the satellites are in near-polar orbits, the track of the flare along the ground is nearly north-south or south-north, and so the direction to the centre is always eastwards or westwards.

Flare centre - Mag.

The magnitude of the flare as it would be seen at the centre.

Sun - Elev.

The elevation of the sun above the horizon at the time of the flare.

Sun - Azimuth

The azimuth of the sun at the time of the flare.

Sun - From flare

The angular separation of the sun from the flare. If the flare is too close to the sun, it will be more difficult or impossible to see.

Satellite

The final column gives the name of the satellite producing the flare. Clicking on the name will take you to that satellite's information page.

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