Planet walk, and Palm Sunday equinox

It’s about 2 AM on Sunday morning, March 20.  We got back yesterday evening from our trip to London and the planet walk on Fortune Green.

Peter Abrahams was the planner, Mark Jacobs was the tour guide for four eager small children and their parents, and Damien Phillips conducted the rest of the equally attentive adults who had shown up on this cold gray afternoon.  (Mark had a clown’s knack with children; Damien told me he was “off form” because he’d had to be up at three in the morning, but if this was so his usual form must be pretty darn good.)  We paused at each planet, that is, at its tree, on which had been fixed an information board including a large picture.

Everyone handles this walk in a different style, and the Fortune Green variation, I would say, was to use light-time, rather than paces, to convey the enormous distances.  That is, the Sun’s rays at their inconceivable speed take 8 minutes to reach this planet (Earth), 4 hours to reach this one (Neptune).

Fortune Green is a triangle of parkland wedged into West Hampstead, and Jupiter came at a hedge that appeared to block the end of it; but a path pierces the hedge and leads on between woods and school playing fields and an extensive cemetery, to the end of the planetary system at another road.

An image occurred to me.  There is a vast galaxy called London.  Out toward its northwestern edge there is a section of spiral arm called Hampstead, and in part of that a starcloud called West Hampstead or West End or Fortune Green Road (there seem to be all those names for the village-like strip that leads to the beginning of the Green), and near an edge of that there is a star called Sun, represented by that Belisha beacon standing where the green begins; and out from that star are the pinheads, peanuts, and prunes that represent its planets.  (Mark and Damien used prunes for Jupiter, equivalent to the chestnut of my model and probably more easily available.)  And farther out are some gravestones and soccer-players who could be various bodies of the outer solar system such as centaurs, plutinos, or Scattered-Disk Objects.

So if, holding on the palm of your hand the peppercorn representing Earth, you were to walk right across London, you would earn a well-earned sense of the insignificant size of our home planet compared with the galaxy.  And yet even this is nowhere near true scale.  If the 2-millimeter peppercorn is the 8,000-mile-wide Earth, your London galaxy, instead of being about 10 miles across, should be about 100,000 miles across.  London is more like the four or five nearest stars.  Next project for the enterprising Hampstead Garden Astronomy Society.

Other impressive statistics are that this team, by the end of the somewhat extended British Science Week, will have done the walk a dozen times, conducting and educating about 300 people, and that’s not counting extra walks carried out by schools.  Peter Abrahams will correct me by a comment here (I hope) if I’ve got any of the facts wrong.

You’re tired, especially if you’ve walked across London, but there’s more that must be mentioned now, because it’s March 20.

It’s Palm Sunday, the end of Lent and the beginning of the week that climaxes with Easter.

It’s also the day of the March equinox; strictly, at 4:30 Universal Time.   – Hey, that’s this very moment!  The moment of the middle of spring in the northern hemisphere.  (Some call it the beginning of spring, but we’ve debated that before, and I have no more to say about it at 4:30 in the morning.)

And at the equinox the Sun enters the astrological sign Aries, though astronomically it’s still back among the stars of Pisces, but that, too, we’ve chewed over before.

Also on this busy Sunday, Venus is at aphelion, the point in its slightly non-circular orbit that is farthest out from the Sun, about 0.73 astronomical units (Sun-Earth distances).

And at almost exactly the same time, around 17 UT, this relatively distant Venus passes half a degree south of far more distant Neptune.  This conjunction is one of the kind to be contemplated rather than seen.  First, the planets are situated 20 degrees west of the Sun, therefore in the morning sky.  The very low morning sky, for our northern latitudes, because of the angle of the ecliptic: below the horizon, in fact, until too close before sunrise.

But for south-hemisphere countries such as Australia, the same cause puts Venus vertically above the rising Sun, and so it may be seen and Neptune imagined beside it.  Venus, though as distant from us as it can get, is still, at magnitude -3.9, far brighter than any star; Neptune, at magnitude 8, is far too faint for the naked eye.

And let’s see what more else can happen.  Well, on this same day and, again, almost at the same time, but over in the evening sky, the Moon passes south of Regulus, the king star in Leo.  But by a rather wide gap of 2.4 degrees.

And also on this same day.  I shouldn’t have time for anything, because what we were really doing in London was looking for a place to lay our heads.  More later.