Why 22 December is actually the longest day of the year

Don’t believe me?  Then watch this brilliant short account of the vagaries of solar time 


Only effective electronic backup for GPS on point of collapse

First the good news.

In October 2014 the General Lighthouse Authorities of the UK and Ireland announced the successful launch of a prototype maritime navigation system called eLORAN. Descended from the old LORAN-C, this ‘enhanced’, digital version can provide positional fixes within a radius of 10 meters and can meet the exacting pilotage needs of ships using UK ports. Best of all it’s completely independent of GPS – and far more robust. According to Professor David Last, one of the leading experts on electronic navigation, the new system is ‘absolutely world-leading’.
Now the bad news. The eLORAN network will be closing down on 31 December because the French and Norwegian governments claim they can’t afford to go on operating the powerful radio transmitters in their territories on which it depends. And unless someone steps in to save it soon, the single UK transmitter may also be shut down, even though it could by itself provide a highly accurate time signal to back up those now derived from GPS.
The vulnerabilities of all global satellite navigation systems (‪#‎GNSS‬) – there are now five of them – have been well known for years. The root problem is that the radio signals from the satellites are extremely weak and have a very long way to travel. It’s bit like trying to spot a car headlight 14,000 miles away – roughly the distance from London to New Zealand. To make matters worse all the 140-odd GNSS satellites soon to be in orbit operate in the same narrow frequency ranges.
Jamming GNSS transmissions is therefore disturbingly easy. Small, cheap jammers readily available on the Internet can block the signal over a few hundred meters. A powerful but still portable device installed at the top of London’s ‘Shard’ could wipe out GNSS coverage from Reading to Southend.
Another big problem is spoofing: transmitting a fake GNSS signal that can make your receiver tell lies about where you are or what time it is – or even shut it down permanently. The North Korean regime has used these techniques to interfere with GNSS reception in South Korea, and there’s plenty of evidence of local jamming either caused intentionally by criminals, or just by accident.

Nature is a threat too. Down at sea level the electronics on board your boat may well go up in smoke if you get struck by lightning, while out in space solar storms can and do disrupt GNSS signals. Human error can’t be ignored either. A fault in the Russian ‪#‎GLONASS‬ system that threw up positional errors of 50 kilometers or more in the North Sea seems to have been caused by someone loading the wrong data.
Of course we now have GNSS chips with everything. Almost every piece of electronic equipment on board a modern ship or boat – radar, electronic chart displays, ‪#AIS‬, radio – is linked to a GNSS receiver. If the GNSS goes down all these systems are likely to go down with it. Not very funny if you’re passing through the Dover Straits in fog. And this isn’t just a problem for mariners. Many other critically important things – like mobile phones, stock markets, banking and broadcasting – rely on the GNSS time signature. The opportunities for criminals and terrorists, not to mention hostile nations, to cause chaos and destruction are all too obvious.
The US military are taking steps to protect their operations against these threats. They haven’t abandoned GNSS, of course, but they employ many other systems to generate the position, navigation and timing data they need. These include tiny inertial sensors, and chip-sized atomic clocks. Just how effective these are is uncertain, but in any case such technology is not yet generally available.
So where does that leave us sailors? The answer is that a black hole will open up on 1 January. There will be no effective electronic backup for GNSS after that date. Offshore navigators will have to dust off their sextants and start talking sights again, because – like LORAN-C – the other radio-based navigation aids have mostly been closed down.
There is however one bit of light on the horizon. The US government is expected soon to announce that it’s going to develop a resilient, publicly available back-up system for GPS, based on the British eLORAN prototype. In these days of budgetary stringency they will probably enter some kind of commercial partnership to deliver the new system.
We can only hope that European governments will take their lead from Washington, rather than continuing to pretend that ‪#‎Galileo‬, Europe’s own fledgling GNSS, will be invulnerable.

In the meantime I suggest you follow the recent example of the US Naval Academy, and start brushing up your celestial navigation!