Iridium is a global network of communications satellites. The system was originally a product of Motorola. Iridium’s 66 satellites provide wireless mobile communications as they move in polar orbits at altitude of 485 mi (781 km). They are able to provide global coverage from pole to pole.
This brief video illustrates the ability of the constellation of satellites to receive a ground signal, pass it to other satellites, then deliver it to the ground in another part of the world.
The original Iridium satellites carry three highly reflective antennae as shown in the image below. Because of their mirror-like surfaces being positioned much of the time in intense bright sunlight, they sometimes reflect a bright spot of light to the ground. The ground track of the reflections is known precisely. If you happen to see it in the sky above, it grows in brightness over a few seconds and can be many times more intense that Venus and then it fades away. They are most easily seen just after sunset and before sunrise. They can also be seen in bright daylight if you know where to look.
Wikimedia | Cliff
I received an email earlier in the week telling me such a reflection, or Iridium flare, was to pass right over my house going south. In fact, another Iridium satellite in nearly the same orbit was to also flare me only 24 seconds after the first. The sky was clear the night of 13 May as I set up for a time exposure photograph.
About 45 seconds before 9:22:14 pm, I started the exposure using NightCap Pro on my iPad 2. The flare maximum occurred as predicted right on time. Coming right behind it was the next one. It passed and peaked at 9:22:38 pm. After 90 seconds I ended the time exposure.
Taken with NightCap Pro | ISS mode | 89.05 sec
How does one know when and where to look? I subscribe to a service called CalSky. It emails me when significant events like this are to occur. It offers many options and services but is not the easiest to use. There are others which are simpler. The best in my opinion for the general user is Heavens Above. In these services, you need to input your location. Heavens Above makes it easy to do by clicking on a map for your location.
Using the CalSky interface, I produced the sky chart of where the Iridium flares were going to pass. It gave this chart making it easy to know where to point my camera.
Launched 15 October 1997, the Cassini Mission is in its 20th year. It reached Saturn and entered orbit on 1 July 2004. Details of the mission can be read at this Wikipedia summary. This post is mostly about the maneuvers by Cassini to change its orbit and make 22 close encounters with Saturn in what is called the Grand Finale. End of mission is scheduled for 15 Sep 2017 when the spacecraft plunges into the atmosphere of Saturn ending a long and brilliant exploration of the famous ringed planet, its rings, and 62 moons.
Clean Room Workers Ready Spacecraft | NASA | 1996
Show me more…
Viewed from Earth, the crescent of Venus narrows each day as it orbits the Sun. On 25 March 2017, it will be aligned almost directly between Earth and the Sun. In the weeks following, Venus will appear as a morning object and a thin crescent. Go here to see a 3D tool showing the orbital positions of the inner planets today. Notice the Date and Date Slider controls where you can change the date and see the planets move.
Venus 15 February 2017
Date Time Digitized: Feb 15, 2017, 6:05:33 PM CST
Exposure Time: 1/500 s
Photographic Sensitivity (ISO): 100
Astronaut twins Mark and Scott Kelly participated in a study conducted by ten researchers on the effects of long duration space flight. Scott was aboard the International Space Station for 340 days while Mark remained on Earth. Scott returned to Earth 1 March 2016. For details about his return, read this previous post.
Ten researchers reported preliminary results on 23 Jan 2017 in Galveston TX of their comparative studies of the twins. The NASA issued statement is here. I’ll attempt to summarize eight of their findings below.
Show me more…
How will the Moon look today, on your birthday, or any date in 2017? Find out at NASA Dial-a-Moon. Enter any month, day, and universal time (UT) hour to see a high definition image. The composite images of Dial-a-Moon are made from those of the Lunar Reconnaissance Orbiter (LRO) in low altitude orbit around the Moon since 2009. Here is the link for southern hemisphere readers.
You may leave the universal time (UT) at the default 1 value. If you are a curious type, Universal time conversion can be done at this link. Enter UTC in the lower right box if it isn’t already set. You can switch from 12 hr to 24 hr at the bottom of the entry boxes. You may also enter any other local time in the upper left box. Go back to Dial-a-Moon to enter the UT.
The collection of accurate images of the Moon for each hour have been made into a movie lasting 5 minutes. Try watching full screen and increase the speed by 2x. Speed can be changed using the gear icon ⚙ after the movie starts. Two versions of the movie are available for readers in northern and southern hemisphere.
I explain the peculiar wobble and tipping motions at this blog post.
Mercury has been visible in the early morning twilight recently. Jupiter is on the opposite side of the Sun from our location. But, Earth is coming around in our orbit catching up to Jupiter. As a result, Jupiter is also a morning twilight object in the same vicinity as Mercury. They were to be very close to each other low in the eastern sky on 11 Oct 2016. Guess what. It was cloudy. But, I did go out on 10 Oct at 6:45 am when it was very clear to capture the view.
The first image is how it looked to my unaided eyes. The second image is zoomed into the center part of the first just above the tallest trees in the vicinity of a faint jet trail.
They are in there somewhere in the middle.
The evening on 9 Oct was also clear. An email notice told me about a bright reflection off of a communication satellite that was to pass right over my location. The satellites are part of the Iridium system consisting of 72 satellites in polar orbits that provide worldwide coverage for satellite phones. Their 3 antennae shown in the image below are flat and highly reflective of sunlight. The positions and angles of each antenna are known allowing predictions of those reflections across the surface of the Earth.
The email notice said the location in the sky was toward 148˚ in the southeast and 50˚elevation. It would last about 10 sec due to the 17,000 mph speed of the satellite.
The sky was dark. I set the camera using a protractor for elevation and Google Earth for direction over my neighbor’s house. I started recording a minute before the due time of 7:52 pm. Success. Here is the video trimmed for time to the actual event.
We were fortunate to have clear sky last evening. The nearly full Moon rose above the southeast. Here it is about 6 hours before full. Full phase was at 4:27 am CDT on 18 August.
According to the Old Farmer’s Almanac, this is known as the Sturgeon Moon.
Some Native American tribes called the August Moon the “Sturgeon Moon” because they knew that the sturgeon of the Great Lakes and Lake Champlain were most readily caught during this Full Moon. They also called August’s Moon the “Full Green Corn Moon.”
Different tribes had different Moon name preferences. Other examples for August are: “Wheat Cut Moon” (San Ildefonso, and San Juan), or “Moon When All Things Ripen” (Dakotah Sioux) or “Blueberry Moon” (Ojibway).