'Up there' is like 'down here'

The picture shows Galileo showing a cardinal one of his drawings of the Moon, obtained using his telescope.

Another cardinal is looking through the telescope. He looks interested in what he is seeing, but the one looking at the drawing does not look at all receptive. To be fair though, Galileo was not exactly skilled at the art of introducing people to new ideas. The drawing can be seen here. https://education.nationalgeographic.org/resource/galileo-discovers-jupiters-moons.

In the 17th century, the picture of the universe generally held, and supported strongly by the Catholic Church, was that humans are the peak of creation and have dominion over the Earth, which is, of course, the only world.

Everything in the sky is very different, perfect compared with the imperfect Earth and of course everything revolves around us. Every day we see it all rise in the east and set in the west.

Being an object in the heavens, the Moon of course had to be perfect, not something smothered in mountains, craters, and, as people thought back then, seas.

Over the following centuries better telescopes, more diplomatic scientists and changing ideas came to show that our Earth is just another planet. The Sun is just another star. Most other planets have moons, in some cases lots of them. However, when it came down to it, we could not see the other planets well enough to compare them in detail with ours.

Mercury, the closest planet to the Sun, lurks in the dawn and sunset twilight and is hard to observe. Telescopes show it as a little disc.

Venus, the next planet out from the Sun was even more frustrating. It is almost the size of the Earth, which makes it more interesting, but its surface is always hidden under a thick layer of cloud.

Mars was, in some ways, even more frustrating than that. Through the best telescopes available it is a small, reddish disc, with white polar caps and irregular dark markings. If you concentrate and stare hard for a long time, as Percival Lowell did, you might start believing you are seeing canals.

The giant planets Jupiter and Saturn are covered with fascinating clouds and Uranus and Neptune are visible only as greenish-blue discs.

Nobody knew about Pluto until 1930, when it revealed itself as a moving dot.

Our ground-based optical and radio telescopes have told us a lot, but our knowledge of the geology, meteorology and biology of other planets was so rudimentary that we had to use our planet as a template to describe other worlds; we just tweaked details until they seemed to fit. Then came the era of space missions, orbiters, landers and rovers, and orbiting telescopes. We could look almost as closely at other worlds as we can look at ours.

Externally, Mercury looks like the Moon but it has a big iron core and a surprisingly strong magnetic field. Venus is a hot world of volcanoes, lava flows and a runaway greenhouse effect. There are no signs of plate tectonics on that planet. Mars is a cold, dry, almost airless desert. However, there are polar ice caps and buried ice. The planet is covered with evidence that billions of years ago it was a watery world with rivers, lakes and seas.

We have learned a lot about Jupiter, Saturn, Uranus and Neptune, but we have yet to fully understand what is going on there. Pluto turned out to be one of the biggest surprises. Although being very cold, it has an atmosphere, is a geologically dynamic world, with its surface is changing over time. As yet we have not found any biology on other worlds, but we are learning how better to search for it.

For me the biggest indicator of how much we have managed to connect what we see around us "down here" with what is "up there" is we can buy comprehensive books on the geology of Mars, the Moon and other worlds.

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• Mercury lurks low in the dawn glow, with Venus to its right. Then, further to the right lie Mars, Jupiter, and then Saturn.

• The Moon will reach its first quarter on June 6.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.