Skywatch Line for Friday, February 19, through Sunday, February 21, 2016

This is Dudley Observatory’s Skywatch Line for Friday, February 19, through Sunday, February 21, 2016, written by Alan French.

A bright waxing gibbous Moon rises in the afternoon and sets before sunrise. Moonrise is at 2:46 pm Friday. It rises at 3:46 pm Saturday and 5:46 on Sunday. The Moon sets at 5:18 am Saturday, 5:56 am Sunday, and 6:30 am on Monday.

It may strike you as odd that the Moon rises an hour later each day, yet the set time changes by less than an hour. This is because the Moon’s path across the sky changes from night to night, and this weekend it travels highest in the sky Friday night and a bit lower each following night.

This area will be treated to a nice pass of the International Space Station (ISS) on Saturday. During the hours just after sunset and before dawn, we are in the Earth’s shadow while satellites, orbiting high above us, are still in sunlight. It is this reflected sunlight that makes them conspicuous. The space station is a very large orbiting lab, so it reflects a lot of sunlight and appears brighter than any other satellite. (To be precise, we’ll talk about a short and brighter exception later in this Skywatch Line.)

The ISS looks like a bright star gliding through the stars. It brightens as it moves higher. I generally find I spot it a little after its “first appearance” time when it has moved higher into the sky. To me, it also seems higher than the maximum altitude implies. Times will be given in hours, minutes, and seconds.

The ISS will first appear in the west northwest at 5:58:24 pm. It will be highest at 6:01:37 pm when it will be 54 degrees above the southwestern horizon. The station drops below the southeastern horizon at 6:04:47 pm.

Its path takes it through the Great Square of Pegasus, below tiny Aries, and it passes below Orion and past bright Sirius as it moves toward the horizon.

There is one type of satellite that can briefly outshine the ISS. More than sixty Iridium satellites, used for satellite phones, orbit the Earth. They orbit from pole to pole, insuring satellite phone reception. Each has three highly polished door sized antennas. At times, an antenna reflects sunlight toward Earth. This brilliant “flare” is visible from a narrow north-south path on the Earth. Fortunately, the orientation of these satellites is carefully controlled, so it is possible to accurately predict where these flares are visible. They can appear brighter than the planet Venus, and so are quite impressive.

The easiest way to see if a flare is visible from where you live or visit is by visiting the Heavens Above Website. When you first visit, click on “Change your observing location.” It is easy to do from the world map. Once you’ve zoomed in and are close to your location, change it to the satellite view. Then click on your house to place a pin and hit the “Submit” button on the bottom of the page. Save the resulting link to your Bookmarks and you won’t have to select your location again.

Once you’ve set your location click on “Iridium Flares” under “Satellites.” You’ll get a list of upcoming flares. If you are close to the center of visibility, they can be as bright as magnitude -8 or even -9. (The larger negative numbers mean brighter. By comparison, Venus is -4.4 at its brightest.)

If you click on the date and time, you’ll get a star chart showing the Iridium’s path across the sky. Over most of the path it may be too faint to see, but as it approaches maximum brightness, marked by the “star,” it brightens and becomes more visible, until it briefly “flares” and becomes extremely bright. Check on a regular basis if you’d like to catch the impressive magnitude -6 to -9 flares.

Below the star chart is a map showing the ground path. By zooming in you can see it in great detail, and it allows you to travel to the center of the path, where the flare will be brightest.

Checking it for Schenectady, from City Hall, I see a -8.3 flare on Monday night. The path along the Earth’s surface runs south to north, so anyone directly north or south of city hall has a chance to see this flare. If the skies will be clear around 6:00 pm Sunday, set up your location at and see if you can see this flare – or another. They’re lots of fun and great to share with friends!

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