I arrived in Hawai’i late last night, fresh – if that’s the right word – from leaving home almost exactly 24 hours earlier. I always find stepping off the plane in Honolulu airport completely disorientating. The accumulated jet lag of a day that never seems to end – an 11.5 hour flight to LA, a ‘stopover’ that as usual consisted of just enough to time to make it through customs and immigration, and then a further 6 hour flight – is enough to make my head spin. Then you have the smell of the place; it smells tropical, and warm, and rich in a way that you notice when the plane doors open even if you can’t see them. Getting to baggage claim involves (at least for those of us who shun the Wiki-Wiki shuttle, Wikipedia’s namesake) a walk outside under a clear sky.
It’s this last detail that stops me dead in my tracks each time. Somewhere along the line I’ve acquired the quintessential amateur astronomer’s habit of looking immediately upwards when walking outside after dark. It’s a quick flick of the head toward the zenith, designed to check if the sky is clear, but it’s become a way of checking that all is right with the world. Even in a city, spotting the bright stars where they should be, night after night, and keeping track of time by following the Moon’s phases is somehow reassuring.
That’s why Honolulu airport gets me every time. I look up, and spot the most familiar of the winter constellations, Orion. The belt points the way to Taurus’ brightest star Aldebaran, and its near neighbour at the minute, Mars. Except that something is different; these familiar friends aren’t at eye level any more, but overhead. Hours spent in the identikit, boring world of international travel boil down to this; I’ve travelled far enough around the world that the view of the Universe is different.
There are other astronomical consequences of being in the tropics, too. Anyone from the UK who finds themselves on a Hawaiian beach watching sunset (or on a Hawaiian mountain top watching sunrise) will be surprised by how fast the action happens. To see why, we need to think about the path of the Sun in the sky.
This path is called the ecliptic, and it lies at the centre of the band known as the zodiac, passing through the 12 traditional zodiacal constellations and a 13th constellation, Ophiuchus. It crosses the celestial equator (the projection of the Earth’s equator onto the sky) at an angle of 23.5 degrees, a consequence of the Earth’s tilted axis.
Now imagine viewing the ecliptic from the North pole. The celestial equator now forms your horizon, and the stars turn around you once every 24 hours, neither rising nor setting. Half the ecliptic is visible, and the angle between it and the horizon is just that 24 degrees. The Sun thus creeps up upon you, moving slowly along the ecliptic to rise just once a year. Away from the pole it’s the rotation of the Earth that matters, not the Sun’s motion, but the principle is the same. The small angle between the horizon and the ecliptic means the Sun just slides out of view.
Head South to the equator. Polaris, the bright star that marks the celestial pole, is now on the horizon, and the whole of the sky will rotate above you once every 24 hours (this is why building astronomical observatories near the equator is a good idea – more of the sky is visible). The ecliptic now makes a much larger angle with the horizon. As the sky rotates, therefore, the Sun is carried straight beneath the horizon in a rapid tropical sunset, an effect clearly visible as I watched sunrise this morning while waiting for my flight to the Big Island.
Both of these effects are a consequence of my chance in latitude; from 50ish degrees north to 20ish. Of course, most of my journey time was spent in travelling in longitude, and working out what longitude you’re at solely from the stars is a much, much more difficult task. But that’s another story.
