Sunday October 25 2020




Village Sky At Night with Brian Watkiss

The moon illusion

Posted on May 22 2013 at 11:24:19 0 comments


Amateur astronomer Brian Watkiss peers into the Village night sky.

June, the month when it never gets dark and the nights get warmer (remember warmer?). The Sun may not go down till after all good boys and girls have gone to bed, but we do have some planets on view.

Venus is with us all month, although very low in the sunset. As it gets higher, the sunset gets later, so you will need to start looking as soon as the Sun dips over the horizon.

Mercury keeps Venus company for the first half of the month but then quickly vanishes after about the 17th. There is a very thin crescent Moon nearby on the 11th.
It is reckoned that only about one per cent of the population has ever seen Mercury, so get your binoculars out (after the Sun has completely gone, of course), find a good view of the northwest horizon, and let’s all become one-percenters.

Looking due south, Saturn appears as soon as the sky starts to darken. Even without any viewing aids, Saturn looks magnificent with its silvery yellow glow – you can see why the Romans thought of it as their god of agriculture.

Through binoculars, you can just about see its largest moon, Titan, although I find I need to steady my arms by resting my elbows on a table. Saturn is with us all month, drifting slowly westwards as the Earth trundles round the Sun. Look for the Moon close by on the 19th.

Full Moon is on the 23rd and, so close to the Solstice on the 21st, it will be very low indeed. This gives rise to the great Moon Illusion, whereby the Moon looks larger than when it is higher in the sky.

That it is the same size there can be no doubt, as it is always roughly the same distance from us – the slight variation in distance is imperceptible to the eye.

That it looks bigger is also true: have a look yourself, as soon as it appears over the horizon just after 9pm on the 23rd. Why this happens is the subject of great scientific debate, but I’m happy just to observe the effect.

Away from the full Moon, perhaps around new Moon on the 8th, this is the time of year to catch a glimpse of Scorpius, the most elusive of the zodiacal constellations. Looking at Saturn, to its right is the star Spica – easy to spot as it is nearly as bright.

Above Saturn and also of similar brightness is Arcturus, the three making a right-angled triangle.Now, you may need to concentrate; at the same height as Spica but at the same distance as Arcturus, to the left of Saturn is the brightest star in Scorpius, Antares.

To the right of Antares are three little stars, forming a vertical line, just discernible in sky glow. And that’s it! That’s all you will ever get to see of Scorpius here in Alvechurch because most of it is below the horizon.

If that has all been too much for you, try going for a little lie down, preferably on the lawn after dark, and look for satellites.

You will be amazed at the number you will see and you can even try competitive satellite spotting. My family have pretended to enjoy this particular sport for years.

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