astronomy

El Terror del Marte

It is hard to imagine what kind of cataclysm could cause Mars to appear as large in the sky as the full Moon, but it would probably mean the destruction of the Solar System as we know it and thus the end of all humankind.

That does not seem to stop the annoying e-mail circulating which says that Mars will be making its closest approach to Earth for 5,000 years (true, but this happened three years ago) and that Mars will look as large as the full Moon.

How could this possibly be true? Mars is about twice the size of the Moon, so a little elementary arithmetic reveals that if it looked the same size, it would be twice as far away; in other words, the Moon would be about half way between Earth and Mars. That’s wrong by a factor of about two hundred. This is the kind of order of magnitude error that you would be making if you thought I was 1200 feet tall, or that England and France are 4,000 miles apart. It’s not even vaguely plausible.

I think this is telling us that we have a worrying lack of basic astronomical literacy. Consider a circulated email which warned that the average temperature in England this summer would be 3,000 degrees Centigrade. This is wrong by approximately the same amount as the Mars meme, yet we wouldn’t give it a moment’s credence. It’s so obviously, hugely divergent from reality that we would assume immediately that it was a joke, or a typo.

It looks as if this is what happened with the Mars alert, as if you read the text carefully you can see that the confusion is caused by a rogue paragraph break:

The encounter will culminate on August 27th when Mars comes to within 34,649,589 miles of Earth and will be (next to the moon) the brightest object in the night sky. It will attain a magnitude of -2.9 and will appear 25.11 arc seconds wide. At a modest 75-power magnification

Mars will look as large as the full moon to the naked eye.

The important bit is easy to miss: at a modest 75-power magnification. In other words, through a fairly decent telescope, Mars will look a similar size to that of the full Moon seen with the naked eye.

But this is stupid! Through a telescope, anything could look as big as anything else! You could say that at a modest 1,000-power magnification, an ant will look as large as a human being to the naked eye. That’s what a telescope is for. It magnifies things.

The circulation of this rubbish has become an annual event and wastes an awful lot of people’s time and inbox space, and the reason I mention it is that I see it has now been translated into Spanish - omitting, of course, the crucial qualifier.

Desmienten rumores sobre acercamiento de Marte a la Tierra (El Universal)

Rumors denied about Mars’ approach to Earth

(quoting from the e-mail)

El encuentro terminará el 27 de agosto, cuando Marte este a 55.439.342 Km de la Tierra. Entonces, junto con la Luna será el objeto más brillante en el cielo nocturno.

The encounter will end on 27th August, when Mars will be 55,439,342km from Earth [true]. At that time it will be, together with the Moon, the brightest object in the night sky.

A simple vista Marte parecerá tan grande como la Luna llena y será fácil de ver.

To the naked eye Mars will appear as large as the full Moon and will be easy to see. [no kidding]

The Bay of Rainbows

I was watching an exciting movie about space (Event Horizon) but I kept noticing actual space out of the window behind the screen; the great shining pregnant Moon riding clouds in a dark sky. I think I would have been all right in the days before telly as I can sit and look at the Moon and stars for hours, as everyone who knows me can testify with some annoyance.

I do not know why I never thought of it before but the little binoculars that Steve the Sheep gave me for bird noticing also come in handy for Moon noticing! Looking at our nearest neighbour with the naked eye is a bit disappointing as you can see a vaguely familiar pattern of dark smudges, or a face, depending how many and what grade of drugs you’ve smoked. But a zoom lens or even the smallest binoculars teleport you into a breathtaking landscape of craters and dark seas, hard-edged and glowing in brilliant sunlight against the pure blackness of space.

It is even more amazing through a decent telescope: the image that swims into focus in front of you is so clear and sharp that it is like looking at really high-quality satellite photographs. You feel that if there were people down there you’d be able to make out their license plates and newspaper headlines. It brings it home to you with a gut immediacy that you are looking down on an alien world, and it’s real.

The photo (by Eric Roel) shows a detail of the Mare Imbrium, the Sea of Rains.

To find it, look for the three roughly similar sized-blobs at the top right of the Moon’s face (if you’re in the Northern Hemisphere, otherwise, the bottom left) and go left to the large dark area above the bright pinpoint crater Copernicus. This is the Mare Imbrium. Now look at the patch of lighter highlands to the north - the ‘shoreline’. There is an almost perfect semicircular notch out of it. This is Sinus Iridium: the Bay of Rainbows. What an amazing name!

You can’t help looking at the Moon differently when you know there’s a Bay of Rainbows up there.

Orion

Orion is probably the most obvious and striking constellation, and it is a great starting point for learning your way around the stars.

You can see that he is raising a club or a spear above his head, and holds a bow - Orion is the great hunter, centrepiece of the winter sky. He is perpetually locked in combat with Taurus, the Bull. Below his belt hangs what we politely refer to as his ‘sword’, though other cultures have identified it with a different item of gentleman’s equipment.

The sword hides a secret. Its middle star is not a star at all, but a vast glowing cloud of gas and dust, the Great Nebula in Orion. This cloud is about 30 light years across, big enough to encompass our Sun and its nearest twenty or thirty neighbours. Inside, new stars are forming with what seem to be the precursors of planets. The Nebula appears unremarkable in visible light, but if we could see in the infrared, it would be a great blazing splash across the sky, four times the size of the full Moon:

(Image from seds.org. This is on approximately the same scale as the picture above.)

Sirius

If you take a line through the stars of Orion’s belt and follow it down and to the left you will come to Sirius, the brightest star of all. Sirius is called the Dog Star because it is in the constellation of Canis Major, the larger of Orion’s two hunting dogs. Sirius is a southerly star, so for northern hemisphere observers it generally appears low on the horizon, like here:

Sirius over Mill Hill village

Procyon

If you look up from Sirius you will see another bright star at the left of Orion, sort of on its own. This is Procyon in Canis Minor, the lesser dog. We’re always hearing a lot about Sirius, but you don’t often see press releases about what Procyon’s up to. It must get a bit frustrating sometimes always being the Number Two. I like Procyon the best.

If you follow a line up from Sirius through Procyon and a bit to the left, hovering over Orion’s shoulder you will see Gemini, the Twins, which we covered in a previous lesson (pay attention at the back).

Aldebaran and the Pleiades

Now go back to Orion and extend the line between Orion and Sirius in the opposite direction. You will come to a bright red star, Aldebaran, the glowing eye of the Bull which always faces Orion. If you keep going you will see a fuzzy patch of middling bright stars, the Pleiades.

Aldebaran and the Pleiades

Happily, Mars wanted to be in this picture too, so it sidled in at the last minute.

Looking more closely at the Pleiades in this 100% crop we can see the Seven Sisters (Alcyone, Merope, Maia, Electra, Taygeta, Celaeno and Asterope) and their parents Atlas and Plione. Alcyone is the eldest sister so she is always in charge if Atlas and Plione go out, which sometimes leads to friction with little Asterope wanting to stay up late and watch TV.

In fact although you can see six or seven stars with the naked eye, there are about 3,000 stars in the Pleiades cluster. That might seem a lot until you realise there about four hundred billion stars in the Galaxy. The Galaxy is so vast that it beggars comprehension. It is about 100,000 light years across, which means absolutely nothing to us humans, but if the whole Solar System were shrunk to the size of a golf ball, the Galaxy would be about the size of North America.

For a minute the Galaxy almost seems impressively large, but it is just one of hundreds of billions of galaxies. There are probably as many galaxies in the Universe as there are stars in our Galaxy. If you start thinking about this type of thing it tends to make your head go a bit woozy and you have to have a sit down. The numbers involved are so much bigger than anything our brains evolved to cope with, we can’t even get a vague sense of the size of the Universe. Whenever you think about it there is a feeling of standing dizzily at the edge of some appalling abyss. Every time you look up into the night sky you are literally staring into infinity.

And we are journeying through that infinite cold, dark void, in a tiny blue spaceship. Unfortunately we are not carrying any spares in the boot so if anything goes wrong with the spaceship, we are pretty much screwed. It is enough to make you drive a bit more carefully.