April 7, 2020

AstroChallenge: Spotting NOSS pairs and Martian Moons.

A NOSS satellite pair plus aircraft… (Photos by Author).

By now, satellites drifting silently in the dawn or dusk skies are nothing new to you, the experienced sat-spotter. But every once in a while, you just might catch a glimpse of something truly weird… This week, we’ll take a look at what are known as NOSS pairs… & “stay tuned” for a teaser for the upcoming Mars opposition and a chance to hunt for its elusive moons.

NOSS stands for Naval Ocean Surveillance System. These satellites were launched in sets starting with the first generation of NOSS satellites in 1976 and continuing through to 2007. They generally appear either as a moving triangle “constellation” or more commonly as pairs. There is some thought that further NOSS sets may even comprise more than three sats; we once spotted a row of five evenly spaced satellites from the Chena Flood Channel in Alaska in the 90s’. NOSS satellites are classified and used to track ships at sea, most notably Soviet subs during the Cold War.

A NOSS pass to the north of Astroguyz HQ.

In our experience, spotting these pairings has been an entirely surreptitious affair; we’ve had four positive sightings in 10 years of serious satellite watching. Orbitron currently tracks 63 NOSS sets in Low Earth Orbit. Most have looping elliptical orbits that guarantee drastically different appearances from apparition to apparition. Generally below the naked eye threshold of +5th magnitude, these satellites can be surprisingly bright if you catch them just near perigee. In my experience, I’ve seen NOSS pairs from middle northern latitudes passing within 30 degrees on either side of the zenith. Both photos included were “lucky shots” when I had the camera at the ready to swing into action while photographing other targets. A concerted campaign to catch NOSS pairs would take into account a careful analysis of the perigee times versus the solar angle overhead; Orbitron, Celestrak and Heavens-Above are all good resources. Hey, I’m refining said technique myself! Another technical dissertation on “NOSS-hunting” can be found here. Drop us a line on thoughts, techniques, and any true tales of sat-spotting!

Orientation of the orbit of the Martian moons; (North is up) note the +12 magnitude background star depicted on February 15th! (Created by the Author in Starry Night).

Also this week, we wanted to issue our challenge on the run-up to the 2012 opposition of Mars on March 3rd to try and spot the tiny Martian moons of Deimos and Phobos. We wrote about this challenge as well as tips and tricks to Martian moon-spotting during the last opposition in 2010, and February-March of this year is a good time to try. The featured strip chart depicts greatest elongation for each respective moon in Universal Time in terms of Mars radii.

Ephemeris of the Martian Moons through mid-March; (Credit: Ed Kotapish).

The asute will notice that areas where the two paths cross, a “Martian moon conjunction” will occur, perhaps raising their cumulative brightness a notch. Yes, this opposition is a particularly unfavorable one, although that shouldn’t stop you from trying. This is because Mars reaches aphelion this week on February 15th at a distance of 154.9 million miles from the Sun, its farthest aphelion since 1995. Thus, Mars will grow from a visual diameter this of 13.1” arc seconds in size on February 15th to nearly 14” in early March. Phobos and Deimos are +12 and 13th magnitude respectively, over 63,000 times fainter than bright -1.2 magnitude Mars. So drag out that light bucket and plop in that occulting bar eyepiece for a chance to replicate the epochal 1877 discovery of these elusive moons by Asaph Hall… expect a full post on the 2012 opposition of Mars at the end of February!