Comet Neowise is here – and it won’t be back for another 6,800 years.
Fantastic photos have shown the comet shooting over various places in the UK and around the world, including Stonehenge in Wiltshire.
The ancient stone circle was just a few hundred years old the last time the celestial body appeared in the sky above Earth.
Ancient peoples – the Neolithic farmers who built the megalithic monument – would have gazed at the comet in wonder and perhaps even fear.
We can only guess at what those prehistoric tribes thought it meant. But in most ancient cultures we know about, comets have usually been regarded as a warning of impending disaster.
The Greeks and Romans saw comets as a sign that something good or bad was going to happen.
A bright comet seen in July, 44BC, was interpreted as the soul of assassinated emperor Julius Caesar being immortalised in the heavens as a divine star.
The Saxons mostly saw comets as bad omens. Halley’s Comet is depicted on the Bayeux Tapestry because it had appeared in 1066, the year of the Norman Conquest.
Months before the invasion, William of Normandy perceived the comet as “a wonderful sign from Heaven” and went on to become the new king of England.
We have no idea what ancient peoples thought of Neowise in its previous appearance when there were no written records, but it’s definitely worth a look as it won’t be back here for many millennia.
Significantly, the comet’s recent journey past the sun – it was at its closest to the sun when 43 million km or 27 million miles away on July 3 – has changed its orbit.
Its orbital period – the time it takes to go around the sun – has increased from 4,500 years to about 6,800 years.
That means it will not come back into our skies for another 6,800 years.
When Neowise returns to earth more time will have passed than the entire history of Stonehenge to date.
What will human civilisation on Earth be like at that point? Will there still be a human race? Will we have left the Earth and be living on space stations or on colonies established on the moon or Mars?
If you haven’t yet seen Neowise streaking overhead, there’s still plenty of chance.
The comet should be visible for most of July and possibly until mid-August.
It’s coming closest to the Earth on July 23, meaning it will look biggest and brightest – though it will still be about 64 million miles (103 million km) away so no need to worry about a collision.
By early July, after its close approach to the sun, the comet appeared to have developed a second tail.
The upper tail is made of ions – these are charged particles of gas caused by the comet getting relatively close to the sun’s intense heat.
The lower, broader tail is made of dust flying off the surface of the comet and trailing behind.
Comets are often referred to as ‘dirty snowballs’ and the nucleus of this particular comet – its solid part made of a lump of rock, dust and frozen gas – is estimated to be 5km (3 miles) across.