Iridium Flares

Transient Events

There are 66 active Iridium satellites providing worldwide coverage for satellite phones. Each satellite has large flat surfaces that can reflect sunlight towards locations on Earth when everything is lined up properly. Some of these flat surfaces are antennas, and some are solar panels. The first picture below shows an Iridium satellite. The gold colored surfaces covered with squares are "door sized antennas" according to Wikipedia. You can also see one of the solar panels on the left.

When you are in the right observing location at the right time of day it's possible to see a temporary bright "flash", or flare, from one of these satellites when sunlight reflects from a flat surface towards you. Some of these flares are very bright. I've seen a particularly bright one appear in blue sky before sunset!

On the evening of November 19th I made the first attempt to capture an Iridium flare with my phone camera. Since flares usually last only a few seconds, and the maximum phone camera exposure time is 10 seconds, the shutter release needed careful timing. I tried to have the exposure begin 5 seconds before the predicted flare time. The timing was fairly good as you can see in the first image below which shows the flare as a short bright streak left of center.

This flare occurred against the background constellation Aquarius. Aquarius and Capricornus are most prominent in the image. Moonlight illuminated patchy clouds. The brightening appears asymmetrical. Either the exposure didn't include both the increase and decrease in brightness, or there was a particularly sudden increase of brightness. This flare was from Iridium satellite 64 and was predicted to be magnitude -7.4, brighter than everything normally in the sky except a full Moon and the Sun.

On December 10th another dimmer Iridium flare occurred near the same section of sky in the constellation Cetus. In this case it was Iridium satellite 47, and the flare magnitude was only 0.4. The next image shows the brightest part of the flare I was able to capture. You can see how dim it was compared to the Iridium 64 flare on November 19th.

This time I was able to get a sequence of three images over a span of 43 seconds showing the satellite's trail as it dimmed and moved from Cetus into Sculptor toward the southern horizon.

Iridium flares would look great in a continuous video. Unfortunately, as I mentioned in the last post, phone camera videos aren't sensitive enough to show stars. A phone video would show only a moving temporarily brightening and dimming light against a blank black background.  

Space Station

Orbital Motion

I continued to experiment with my phone camera on November 28th as the International Space Station traveled through the constellations Draco and Ursa Minor in early evening. The Moon was quite bright that night, so my 10-second exposures at ISO 800 did not reveal a dark background sky. The bright streak in the center of the first picture below is the trail made by the Space Station during one 10-second exposure. You can also notice the dim trail of either an airplane or another satellite moving diagonally through the upper right of the picture.

Next is a 6-frame animation of the Space Station's motion covering approximately 2.25 minutes of elapsed time. Since the phone camera has a maximum exposure time of 10 seconds, there are missing gaps in the continuous Space Station path. I repeatedly pressed the shutter as fast as I could, but I included an automatic 2-second delay between pressing the shutter button and exposure initiation to let vibrations die down. Notice how the Space Station gradually fades away in the last frame. An unknown satellite or airplane streaks diagonally through the upper right.

The Space Station's altitude is approximately 260 miles, and it moves at roughly 17,130 mph! At this speed it can travel 1,000 miles in about 3.5 minutes!

My next attempt to capture the Space Station happened on December 15th. This evening the Moon was below the horizon, and the sky was dark when the Space Station passed nearly overhead. The next image shows 10 seconds worth of orbital motion as the station passed near the constellation Lacerta heading toward the Great Square of Pegasus. Cepheus, Cassiopeia, and Perseus are seen from left to right along the bottom of the picture. The Andromeda Galaxy is the tiny fuzzy smudge slightly to the right of center.

I misjudged the location of the Space Station's path as it passed near the zenith, so the previous picture shows the track off center. As the orbit continued I was able to get three consecutive images while the Space Station descended toward the southeast. The following 3-frame animation captures 40 seconds of motion and shows the path dropping through the constellations Pisces and Cetus toward the murky light polluted horizon.

I tried using the phone's video recording mode to capture continuous motion of the Space Station through the constellations. If the Space Station is bright enough, the phone camera detects it as a moving point of light, but the background stars do not show up during the short time exposures of each video frame. Thus, choppy animations like the two shown above are the best I can do with the phone to show orbital motion among the stars. 

Nightscapes With a Phone Camera

Sky Scenes

I've been exploring the ability of my Samsung Galaxy 8 Plus phone to image constellations. The maximum exposure time in the "pro" setting is 10 seconds at ISO 800. Only limited faint detail can be captured, but I'm amazed at how well the tripod-mounted camera works at night.

For example, look at the next picture of Orion rising among moonlit clouds on November 27th. Auriga, Taurus, and the Pleiades are also visible.

The next night, November 28th, I captured the same scene when clouds were absent. Constellations are easier to see, but the Moon was one day closer to full. Consequently, the sky is bright.

On December 10th moonlight was absent in the evening. I walked away from neighborhood lights to take pictures in a nearby field. The next image shows a noticeably darker moonless sky as Orion, Taurus, and the Pleiades shine above bare trees.

Trees make a nice foreground in the previous picture, but the branches are very dark. It would be nicer if the branches were slightly illuminated. I next moved to a place where local lights were blocked by surrounding trees and got the following image of Auriga centered between the trees. Perseus, Taurus, and the Pleiades are also visible.

In the previous picture (and others) the image center is noticeably brighter than the upper edges. I wonder if the camera chip is more sensitive in the center, or if there is vignetting. This effect could be removed by flat fielding, but I didn't take a flat field image.

Finally, I walked further away from neighborhood lights to capture the following picture of Orion, Taurus, Auriga, and Gemini rising above pine trees in a nearby soybean field.

I've tried doing constellation photography with my Nikon DSLR, but have encountered several frustrating obstacles. The Nikon will not automatically focus on stars, so I need to manually focus. Unfortunately, the infinity setting for manual focus is not accurate. This means I need to rotate the focus ring back slightly away from infinity and then visually check to see if stars are focused. The visual checking requires several time exposures and subsequent magnifications of the viewing screen in order to see if stars appear as points. While this tedious exercise is going on my hands are getting numb and the camera lens is getting covered with dew. The Nikon DSLR can do long exposures on the "bulb" setting, and this reveals lots of dim stars and faint details. But these long exposures require a tracking mount to keep up with Earth's rotation. On many occasions I've spent the better part of a freezing, hand numbing hour setting up the tracking and focusing the camera only to find the lens covered with dew and useless.

In contrast, the phone camera quickly focuses automatically and does a good job showing the brighter constellation stars. The phone lens doesn't seem to get quickly covered with dew the way my DSLR lens does. Ten second exposures don't require guiding equipment to follow Earth's rotation. The phone/tripod combination is easy to carry from place to place and sets up quickly.

Images like the ones above can easily show satellite and meteor tracks among the constellations even if dim stars are missing. I hope to capture some of these events and display the results in the next few posts.

Nutcrackers Galore!

Christmas Decorations

There's a nice little restaurant here in Williamsburg called, Victoria's. Near Christmas it's decorated with an astounding collection of nutcrackers! Here's what you see when you enter.

The entrance display is only the beginning. A table near the entrance has this view.

Tables on the right see this side of the central display.

Tables on the left see the other side of the central display.

And there's even more!

Where in the world did they get so many nutcrackers? Victoria's is a lovely place to get breakfast, especially near Christmas!