The Night Sky July 2018
I have to admit that I am not a big fan of the moon! Particularly the weeks either side of a full moon. It blazes out dazzling light and can drown out even the brightest of stars. A better time is when the Moon is New (no glare at all, this month 13th July). However, I am aware that without it we all may never have evolved and the tides it creates may have been instrumental in life emerging from the sea to the land. So fan or not, I’m glad it’s there! It is also a good target to view for those of you without telescopes, especially during the summer when dark nights are short. So this article is devoted to our closet celestial body.
The Moon.
The moon is thought to have been formed not long after the Earth about 4.5 billion years ago. No-one knows for sure how it was formed but the general view is that it was formed from the debris of a collision between the Earth and another large planet-sized body.
The Moon has retained the scars of being Earth’s shield and its own geological history for billions of years. There is no water to erode the surface or significant atmosphere to weather the landscape. Many processes that change the surface here on Earth are not present on the Moon. Had the Earth been exposed to the same bombardment from space, without our gravity, atmosphere and weather systems it would perhaps look like the moon today. The evidence of some craters are still present on Earth but not as obviously defined as they are on the moon.
The Moon’s rotation is locked as it rotates around the Earth, always showing the same ‘face’ towards us, called the ‘near side’. So we always have the same view and which can help us become familiar with its surface and features.
Looking at the moon you will see grey patches. These are ‘Seas’ (Mares) - large areas filled with solid lava rather than water. The most famous being the Sea of Tranquillity, where man first set foot on the Moon. Even with the naked eye you can see craters on the Moon. This is astounding as it’s a quarter of a million miles away. One of the easiest to spot, Tycho is a 53 mile wide crater, in the southern part of the moon. (roughly the distance of Embsay to York, see what this would be like in my diagram.) It has one of the brightest craters and is therefore one of the youngest. It is at the centre of an extensive ‘ray’ system stretching across the surface of the moon. Rays are streaks of debris that seem to come from some of the larger craters. Inside the Tycho crater is a high peak over a mile high that can be spotted with a modest telescope.
In the early years of medicine it was thought because the human brain was made up mostly of water that the full moon’s gravity befuddled your sanity (like the Moon affects the tides) and hence the word ‘lunatic’ was born. So beware the Full Moon of 27th July! You may think you are going mad as you see a very large reddened moon rising as the moon is eclipsed at 8.47pm for an hour and half (10.13pm). The red colour is the effect of the sun’s rays passing through our atmosphere and filtering out particular wavelengths as it hits the moon’s surface.
The Moon illusion.
The moon appears bigger when near the horizon because of an optical illusion. When the moon is high up in the sky there are no reference points to judge its size and humans are notoriously bad at judging vertical distance. Nearer the horizon, our brain perceives vertical distance differently as familiar objects such as trees or buildings are helpful points of reference. Also perspective can play tricks with your mind! (See diagram.) To this day no one can really agree on why this illusion takes place. Some people argue it is an illusion similar to the one in the diagram. What do you think?
On July 27th Mars is in opposition (see last month’s issue regarding ‘opposition’). I would not normally suggest viewing during a Full Moon but it should be a special evening. You should see Mars low in the sky with a full Moon being eclipsed very close by and to the right in the south beautiful Saturn. What a view!
Kommentare