I spy with my (unaided) Eye...

For the amateur astronomer to explore and enjoy the wonders of the night-sky it’s essential to have sort of equipment for viewing. Telescopes are best, of course, but even a good pair of binoculars can be very useful (See elsewhere on this site for information on suitable equipment).

But there’s a whole treasure trove of extraordinary and beautiful phenomena to be seen in the night-sky for which no viewing equipment is needed. These are the naked-eye events and objects that anyone can see and enjoy provided they know when and where to look for them.

Below is a list of natural wonders which can be seen without any optical aid.

Aurora Borealis

Also called the ‘Northern Lights’ or ‘Polar Lights’, the aurora is one of the most beautiful light-shows that the human eye can see.

Above the northern horizon the sky begins to lighten before a distinct glow blooms into an arc of light. That arc rises into the sky sending up streamers before spreading itself into an ‘upside-down’ curtain of shimmering, multi-coloured ripples and folds. Waves of light then shoot up towards the zenith before slowly fading away.

These displays can last from a few minutes to several hours and are caused by the sun emitting electrified particles – solar wind - which race across the 93 million miles to the Earth. Because these particles are magnetised they head for the earth’s magnetic poles and it is for this reason that aurora displays are best seen from higher northern latitudes.

During the long winter nights in Northern Scandinavia, for instance, aurora displays can be almost continuous; residents in Northern Scotland are pretty well assured of several decent displays each year while for the people of Southern England and the West Country, the Polar Lights are rare events.

However, one never knows: there was a truly spectacular display seen from the Sussex Coast in 1938 and another which was widely seen across Southern and Central England in 1961.

That’s part of the fun and excitement that comes with astronomy; one never knows whether today will be the day!

Aurora Australis

Also known at the Southern Lights, the Aurora Australis is pretty much identical to the Aurora Borealis – just substitute the word ‘south’ for ‘north’ and you have it. Can displays of aurorae be predicted? Not really: there is evidence that good displays are linked to magnetic storms - themselves most likely during the peak of the 11-year sunspot cycle. However, there are never any guarantees and the best advice is to keep watching the skies...

Meteor Showers

Another natural phenomenon visible – indeed, best seen – with the naked eye. There’s a fairly good chance of seeing a meteor shower due to the fact that there are several displays each calendar year – and they are highly regular events.

Meteors are tiny pieces of cosmic rubble ranging in size from a grain of sand to a grape. These ‘shooting stars’ are believed to be the remnants of disintegrated comets which continue to orbit the sun. When our planet intersects their own orbital path, these tiny particles are pulled towards us whereupon they are heated to destruction by friction as they encounter the upper atmosphere.

Because these remains are orbiting the sun in parallel paths the meteors in a shower will all appear to emanate from the same point in the sky – called the radiant. It’s this radiant which gives the shower its name: for example, the meteor shower we see in the middle of August each year seems to emanate from a point within the constellation of Perseus. For this reason, the shower is known as the Perseids.

The best of the showers are:

Quadrantids - Early January – actually in the constellation of Bootes
Lyrids – Mid-April – in the constellation of Lyra
Aquariids – Early May – in the constellation of Aquarius
Perseids – Late July – in the constellation of Perseus
Orionids – Mid-October – in the constellation of Orion
Taurids – Late October – in the constellation of Leo
Leonids – Mid-November – in the constellation of Leo
Geminids – Early December – in the constellation of Gemini

Comets

For centuries, comets were hailed with dread and dismay on earth and were believed to be the harbingers of doom and destruction. A representation of the famous Halley’s Comet can actually be seen in the Bayeux Tapestry which was made to commemorate the Norman Conquest of 1066.

Like meteor showers, comets belong to our solar system and make their own orbits – usually highly elliptical ones – round the sun. For most of the time they are just big lumps of rock, rubble, dust and ice which hurtle through space; it is only when they approach the sun and start to heat up that their distinctive tails develop as some of the ice starts to melt and that dust is released.

Comets can be very hit or miss. Halley’s Comet, for instance, passes the earth regularly every 76 years. Its appearance in 1910 was, apparently, spectacular and dominated the night sky for several weeks; but its eagerly anticipated reappearance in 1986 was a huge disappointment. Unfortunately, the comet and the Earth were on opposite sides of the sun and many people never saw it at all.

In recent years, the 1997 appearance of Hale-Bopp was the best for many years. However, when you bear in mind that Comet Hale-Bopp was only discovered in 1995, you can see that comets are highly unpredictable things. It may well be that there is an even bigger and more spectacular ‘space snowball’ which is, at this moment, hurtling towards us from the depths of space and of which we know absolutely nothing.

Solar Eclipse

A total solar eclipse is probably the most spectacular light-show that nature provides. Briefly, day is turned to night and the Sun’s corona becomes visible. One of the reasons that a total eclipse is so spectacular is that the discs of the Sun and the Moon respectively are exactly the same size - as seen from the Earth – so one can fit almost perfectly over the other. So precise is the match that a total eclipse creates what’s called the ‘diamond ring effect’ when the rugged terrain on the limb of the Moon, allows beads of light to pass through the Lunar mountainous valleys to the observer on Earth: a remarkably beautiful optical effect. Unfortunately, total eclipses are extremely rare things for any one, specific location on our planet and the next one visible from the UK won’t be until September 2090 – although other parts of the world will be more fortunate.

WARNING: Under no circumstances should you ever attempt to view the Sun directly through binoculars or a telescope. Severe retinal damage and even blindness can result – even when the Sun is cloud-covered and seemingly comfortable to view with the naked eye.

Green Flash

The Green Flash is another optical phenomenon seen shortly after sunset or before sunrise when a bright green spot is visible just above the sun. Sometimes the Green Flash appears as a ray of green light shooting upwards from the sun’s edge. On occasions, it’s so strong that everything to the observer turns briefly green. They are best seen on an unobstructed horizon – such as over the sea - and are more likely when the intervening air is clean and clear.

The Green Flash is a fleeting thing and only lasts for a second or two. For this reason, few people have seen one and, even when conditions are perfect, there are no guarantees.

The flash is actually caused by refraction when the higher frequency green/blue light from the sun remains visible to the observer after the lower frequency red light is blocked by the curvature of the earth.

Lunar Eclipse

More frequent if less spectacular than a total solar eclipse, the lunar eclipse is still a fascinating thing to see and can be quite beautiful with the Moon taking on a variety of colours – from violet to blood red – as it passes through the Earth’s shadow.

A total eclipse occurs when the Sun, the Earth and the Moon are all aligned with the Earth in the middle. For that reason, a total lunar eclipse will always occur when the Moon is at the full and, because the Earth is so much bigger than the Moon, the whole lunar surface is covered by our planetary shadow.

Unlike a solar eclipse, a lunar eclipse can be viewed from anywhere on the Earth where it is night although it won’t be total everywhere; also unlike a solar eclipse, a lunar eclipse can last for several hours.

The last total eclipse was well seen from the UK in December 2010. Unfortunately, we have now entered a rather barren period and the next guaranteed total lunar eclipse will not be seen until September 28, 2015.

Zodiacal Light

This is another of nature’s light-shows to be seen in the night sky like the aurora but is much less spectacular and much more elusive. It takes the form of a triangular or cone-shaped radiance seen after dusk in the west or before dawn in the east.

The Zodiacal Light extends upwards along the path of the sun through the sky – called the plane of the ecliptic – and is best seen in the late evenings of March or the early mornings of September as those are the times when the ecliptic is at its steepest angle to the horizon.

The Zodiacal Light is actually caused by sunlight reflecting off a mass of dust particles which lie in a lens-shaped disc centred on the Sun and spreading out well beyond the Earth’s orbit. This fine debris is known as the Interplanetary Dust Cloud or Cosmic Dust.

At its brightest, it is comparable with the Milky Way.

Gegenschein

Gegenschein is a German word meaning ‘counter-glow’ and was the term coined for another light phenomenon that can be observed in the night sky.

Like the Zodiacal Light, the Gegenschein is caused by sunlight reflecting off interplanetary dust. Unlike the Zodiacal Light, the Gegenschein will always be seen in a point of the sky which is directly opposite to the position of the sun. It appears as an oval-shaped patch some 30-50 times the width of a full moon. Both the Zodiacal Light and the Gegenschein are delicate and elusive phenomena and both are easily overcome by light pollution. Indeed, many professional astronomers will admit to having seen neither. Your best chance is in a location where there is clear, clean air and where artificial lighting is as far away as possible – not easy in this modern, congested world.

The Milky Way

Sadly, there are many people who have yet to see the Milky Way, that broad sweep of pale light that crosses the night sky.

Why? Light pollution again; but, find yourself a dark spot well away from the sodium city glow in the sky and it’s a wonderful sight. It can stretch from horizon to horizon.

What are we seeing? Well, to look up at the Milky Way is to look sideways through our own galaxy and, if you focus towards the constellation of Sagittarius, you are actually looking towards the very centre of our own Milky Way Galaxy.

The Andromeda Galaxy

To many people, there is one small, fuzzy patch of light visible on a dark, clear night which represents one of the most amazing sights in the night sky.

It is the Andromeda Galaxy – so called because it can be seen within the constellation of Andromeda. In fact, the Andromeda Galaxy has nothing to do with Andromeda at all because it is, in effect, a galactic next-door neighbour and a staggering 2.5 million light years from Earth. Some estimates have suggested it could contain a trillion stars.

For many years, it was thought to be the nearest galaxy to our own Milky Way although that honour has now passed to the Canis Major Dwarf Galaxy. However, Andromeda is still seen as our nearest neighbour of any consequence in terms of a large, spiral-arm galaxy, similar to our own. Indeed, an observer situated on a planet somewhere within the Andromeda Galaxy who looked towards our own Milky Way Galaxy might well see pretty much what we see when we look in the other direction!