The solar system and the Blitz

From planets to specks of dust in meteor showers, there are many kinds of solar-system bodies, and how do we classify them?

By size? Or by composition? – rock lumps like asteroids, vaporizable snowballs like comets. Or by orbit? – satellites go around primaries, Trojans hovering at positions in Jupiter’s orbit, Trans-Neptunians are beyond the planets, dwarf planets have not gravitationally “cleared” their own orbits, types of near-Earth asteroids are distinguished by whether their orbits cross Earth’s or almost touch it from outside or inside.

All of the above.

In other words, categories overlap, as the Euler diagram tries to summarize.

It has been a problem area in the new Astronomical Companion that we are preparing. I felt that we need a “Solar System” introductory chapter, and not only a list of definitions but a graphic of those near-Earth orbits.

The bar for each asteroid represents the range of its orbit, from perihelion out to aphelion, 1 AU (astronomical unit) being the average radius of Earth’s orbit.

This kind of diagram might usefully show a pattern with a far larger number than available to me and with the orbits sorted into types.

Here is something more fun. A top-down view of the orbits of the four type asteroids of the near-Earth kinds.

I’m showing only part of this picture because it is a large one. It’s a 3-D view, from a distance of 7.5 AU (about 1,122,000,000 kilometers) north of the Sun, as you can sense from the “stalks” connecting the bodies to the ecliptic plane at 1-month intervals.

Apollo, Amor, and Aten have long been famous as type asteroids. But the most recent, Atira, discovered in 2003, is perhaps even more interesting. It began a new class: those with orbits entirely inside Earth’s. And it is a rare instance of a binary asteroid: the primary and its satellite, 3 and 1 kilometer wide.

And its name? There is an evident tradition of A- names for these type asteroids. Apollo, Greek god of enlightenment and sunlight, Amor, a Roman personification-deity, Aten the beneficent Sun with whom Ra was temporarily replaced by the monotheistic pharaoh who renamed himself Akhenaten.

Minor planet 163693 was one of the many discoveries of LINEAR (Lincoln Near-Earth Asteroid Research) with its instrument near Socorro, New Mexico, and was given the name of the Earth goddess of the Pawnee, a Plains tribe who lived in Nebraska and Kansas.

Solar System as relief from the Bombs

There is at present an exhibition at St Paul’s cathedral about the struggle to protect it during the Blitz, the bombing of Britain and especially London by the German air force from 7 September 1940 to 11 May 1941.

From where we now live, we had only to go across the Millennium Bridge and up the walkway to the cathedral.

The exhibition is in the churchyard on the south side.

It has been ingeniously assembled on what you might call monoliths or stelae – square pillars – somewhat like the design used at the holocaust memorial in Amsterdam.

The story is clearly told.



The Watch volunteers were doctors, government employees, nurses, lawyers, teachers, ordinary people. They risked their lives as they carried precious items out of the building, and shifted rubble to rescue the wounded.

Here’s an unidentified member.

Each night they gathered in the maintenance workers’ mess room and listened to the radio news of the war.

Training was boring. So it was varied with lectures on a variety of subjects. “Women in Romantic Poetry”; “The Solar System.”..

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