Artificial Flares

What is an Iridium Flare?

An Iridium Flare occurs when sunlight is reflected off an Iridium communications satellite in low orbit around the Earth. The satellite has three door-sized reflective antennae which, if they catch the Sun’s light correctly, reflect it back so that it can be seen at certain locations on the Earth's surface.

What’s so special about an Iridium Flare?

The reason why Iridium Flares are so popular is because the flare they reflect back to Earth can appear very bright as long as you happen to be in the right place at the right time. There’s also an increased likelihood of seeing one because Iridium describes a constellation (that’s the collective noun of a group of satellites) of satellites – in other words there’s more than one.

The name Iridium was initially chosen because 77 satellites were planned. This being the atomic number of the element Iridium, that's where the name came from. The fact that there are so many Iridium satellites in low Earth orbit also increases the chances of being able to see a flare.

What do you need to see one? Nothing apart from clear skies and your own eyes. Iridium Flares vary in brightness from that of bright stars up to appearing much brighter than the planet Venus. If you see a really bright Iridium Flare, trust me, it’s something you won’t forget in a hurry!

How can you tell when one is about to appear?

Iridium Flares from specific Iridium satellites are visible in a defined location. The flare will appear brightest at the centre point of this location dimming the further you are from that point.

The best way to get a prediction is to visit the www.heavens-above.com website, specify your location and generate a list of predictions. To help you, I’ve put together some simple step-by-step instructions below.

How to get and interpret Iridium Flare predictions...

Step 1: Access the www.heavens-above.com website.

Step 2: Under the “Configuration” section click on “from database

Step 3: Click on the letter your country name begins with. I’m in the UK so I would click on “U

Step 4Click on your country name. Again, as I'm in the UK I would click on “United Kingdom”.

Step 5: Enter the name of the place where you live. The database is quite extensive so if you live in a small village, try entering it's name first. If that’s not found, then try the next largest place. The town where I live is called Selsey in West Sussex. If I enter Selsey into the search box, the database comes back with the matching entry. To select it, I simply click on the name "Selsey".

Note: If you visit the site a lot, you can register with it to prevent having to select your location each time.

Step 6: Under “Satellites” look for "Iridium Flares" and click on “next 24 hrs

Step 7: If there are any flares visible from your location they will be shown in a table. The result I got for the date I wrote this blog post gives the following results…





Step 8Don’t panic – the table’s really easy to interpret!

The “Date” column gives the date the event will occur on.

Local Time” gives the time of the event. If daylight savings are in force (e.g. the clocks are currently using British Summer Time or BST) then the time is given in BST. If daylight savings is not in force then the times are given in GMT. Basically, the time of the event shown is the same as that currently measured by your watch so you don’t have to worry about adding or subtracting an hour. The flare times are generally very accurate so if you intend to try to see one, make sure your watch is set to the correct time down to the second.

The “Intensity (Mag)” column shows how bright the flare will be from your location. The values are normally 0, -1, -2, -3, -4, -5, -6, -7 and -8. Basically the more negative the number, the brighter the flare will be. A 0 flare will be as bright as a typical bright star. A -1 flare is about as bright as Sirius, the brightest star in the sky. A -2 flare is about the same brightness as the planet Jupiter (and that’s quite bright). A -4 is about the same brightness as the brightest planet in the sky – Venus (and that’s very bright!). A -8 flare is extremely bright and can illuminate thin clouds that lie between you and it! A -8 flare is the one not to miss.

Alt.” stands for “Altitude” and refers to the height of the flare above the horizon measured in degrees. The horizon has an altitude of 0 degrees while the point immediately above your head has an altitude of 90 degrees. So 30 degrees altitude would be one-third of the way up the sky measured from the horizon. 45 degrees would be half way up and so on. Your outstretched hand at arms length is about 25 degrees from thumb tip to little finger tip.

Azimuth” is the direction around the horizon measured eastwards from north. If you face north, that’s azimuth 0 degrees. Turn to your right by 90 degrees and you’ll be facing east which has an azimuth of 90 degrees. Turn right by another 90 degrees and you’ll be facing south which has an azimuth of 180 degrees. Finally another 90 degree turn to the right will have you facing west with an azimuth of 270 degrees. Just to help you, the figures in the table have the compass direction in brackets after them. If you're not sure which way is north, a compass will then help you point in the right direction. Failing that and you're in the Northern Hemisphere, use the two stars further from the handle in the famous "Saucepan" pattern in the sky to point at Polaris (imagine the pan on a flat surface and extend them upwards with respect to it). The rather average looking star you eventually come to, sitting more-or-less on its own is Polaris, the North Star. Drop a vertical from Polaris to the horizon and that's north.

Distance to flare centre” gives the distance and direction you’d have to travel in order to see the flare at its maximum brightness. Don't worry about this unless you intend to travel to where the flare will appear at its brightest. 

Intensity to flare centre (Mag.)” gives the brightness of the flare you’d see if you followed the directions in Step 14 and travelled so that you were under the flare centre.

Satellite” is the name, or rather number, of the satellite which is causing the flare.

Step 9: Go out a minute or two before the predicted appearance of the flare and stare at the area of sky where it should appear. The movement of the satellite will be obvious after a few seconds even if you're not looking directly in the right place. 

A flare starts off as a relatively dim dot which progressively gets brighter and brighter before giving the peak glint at the predicted time. After this the reverse occurs with the satellite gradually dimming back to obscurity. The whole thing normally takes around 20-30s to complete.

A flare from a specific satellite is a relatively local event typically only noticeably visible for approximately 50km from the central location point. Consequently, if you have a really bright one predicted for your location there’s little point in phoning a friend who lives at the other end of the country to tell them to look out for it, because they won’t see the same satellite flare. They may however, be able to see a flare caused by another satellite so send them these instructions to them to help them find their own events.

Good flare hunting!

 

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