Strange moons and raging storms in clouds of blue: The twin planets Neptune and Uranus make a close appearance this month. Heather Couper and Nigel Henbest explain their characteristics

IF YOU are a dedicated planet-spotter, you may want to try searching this month for two worlds close to the very edge of our solar system - Uranus and Neptune. With binoculars or a small telescope, you can spot them in the constellation of Sagittarius. They appear a couple of moon's widths apart - this is one of their closest approaches in centuries - as they drift slowly westwards together during the course of the month. Both planets are newcomers to the solar system - at least as far as our knowledge about them is concerned. Like Earth, they have been around for nearly 5 billion years, but because they are so remote they came to light only relatively recently.

Uranus was discovered accidentally in 1781 by an amateur astronomer called William Herschel. King George III was so impressed that he instantly made Herschel his personal astronomer. Neptune came along in 1846, and owes its discovery to the power of mathematics. Astronomers realised that a mystery object was pulling Uranus off course in its orbit, and calculated where the culprit should lie. Neptune turned up bang on target, leading to an argument as to over who had actually had discovered it.

Until recently, very little was known about these remote worlds. Both turned out to be smaller versions of the gas giant Jupiter (but four times bigger than Earth, none the less), with small families of moons - Uranus with five, Neptune with two. They were often regarded as 'twin planets'. The only unusual feature of these worlds was Uranus's tilt - it circles the Sun on its side, tipped at 98 degrees from the vertical.

The two planets might have languished at the edge of the solar system for years had not the controllers of Nasa's Voyager 2 space probe pulled off a brilliant bit of 'interplanetary snooker'. By using the gravity of Jupiter and Saturn to catapult the probe towards a target, Voyager 2 was able to fly past Uranus in 1986, and Neptune in 1989.

Uranus was boring. It is a blue-green gas giant so featureless it took considerable computer-power to reveal one insignificant white cloud. However, Voyager 2 was able to confirm the existence of thin rings around the planet and imaged a handful more. But it was Uranus's moon system, now known to number 15, that stole the show. In particular, Miranda, at 500km (300 miles) across the smallest of the previously known moons, has a geology that defies description. It has chasms 10 times deeper than the Grand Canyon, and features that look like cosmic racetracks. Some scientists think Miranda was blasted apart by a huge impact, after which it reassembled itself in space.

As Voyager 2 drew closer to Neptune in the summer of 1989, it quickly became obvious that Neptune was far from being Uranus's twin. True, the planets are the same size; but Neptune turned out to be anything but boring. It is a beautiful turquoise world, its cloud-tops flecked with fleecy white 'cirrus' and midnight-blue spots. The biggest spot of all - the Great Dark Spot - is a raging storm the size of the Earth. Around it blow winds with speeds of up to 2,000kph (1,250mph), the fastest winds in the solar system.

The planet is surrounded by four rings, and circled by eight moons. One, Triton, is the coldest place in the solar system. Scientists were astonished to discover that it has volcanoes that spout nitrogen and black dust high into its thin atmosphere.

Why are Uranus and Neptune so different? It may be due to internal activity: Neptune actually radiates more heat than it receives from the Sun. But it may also be that Uranus was hiding its light under a bushel when Voyager 2 paid its visit.

Three months ago, the American astronomer Walter Wild used a technique that cancels the blurring effect of Earth's atmosphere to make images of Uranus with a multiple-mirror telescope in Arizona. He found a dark spot on Uranus at almost exactly the same latitude as the Great Dark Spot on Neptune, along with a bright region and a faint band near the pole. 'It probably just had a few bad weeks when Voyager passed by,' Mr Wild says.

THE PLANETS

It is not the best month for planets. Those with an extremely good western horizon might spot Jupiter and Mars (just two moon's widths apart 4-6 September) setting about half an hour after the Sun.

But the planet that holds centre stage at night is Saturn, shining brightly in the rather barren constellation of Capricornus. The angle the rings present to us is closing up, so take a look now (with a small telescope) because things won't get much better until 1998.

Early-risers will get gorgeous views of Venus, which rises two to three hours before the Sun. If you can catch it on 2 September, look at it through binoculars - it makes a very pretty sight.

If you think the chart looks strange, with two full moons - there isn't a mistake. Every two years or so we get two full moons in the same calendar month.

THE STARS

Lying just below the 'Summer Triangle' of Deneb, Vega and Altair is one of the smallest and most charming constellations in the sky - Delphinus, which looks like a tiny dolphin.

There is nothing terribly special about the stars of Delphinus. There is, however, a fascinating tale associated with its two brightest stars. Generally, the brighter stars have Arabic names, but these two hail by the decidedly un-Arabic Sualocin and Rotanev. If you read the names backwards, all becomes clear. They spell Nicolaus Venator - the Latinised form of the name Niccolo Cacciatore, who was assistant to the 18th- century Italian astronomer Giuseppe Piazzi.

SEPTEMBER DIARY

(all times BST)

1 3.33am Full moon

9 7.27am Moon at last quarter

16 4.10am New moon

22 8.32pm Moon at first quarter

23 1.22pm Autumn Equinox

30 7.54pm Full moon

(Graphic omitted)

Suggested Topics
News
peopleHowards' Way actress, and former mistress of Jeffrey Archer, was 60
Sport
Romelu Lukaku puts pen to paper
sport
News
Robyn Lawley
people
Arts and Entertainment
Unhappy days: Resistance spy turned Nobel prize winner Samuel Beckett
books
PROMOTED VIDEO
News
people
Life and Style
Troy Baker and Ashley Johnson voice the show’s heroes
gamingOnce stilted and melodramatic, Hollywood is giving acting in video games a makeover
News
i100
Life and Style
Phones will be able to monitor your health, from blood pressure to heart rate, and even book a doctor’s appointment for you
techCould our smartphones soon be diagnosing diseases via Health Kit and Google Fit?
Travel
Ryan taming: the Celtic Tiger carrier has been trying to improve its image
travelRyanair has turned on the 'charm offensive' but can we learn to love the cut-price carrier again?
News
people
Extras
indybest
News
ebookA unique anthology of reporting and analysis of a crucial period of history
Sport
Usain Bolt confirms he will run in both the heats and the finals of the men's relay at the Commonwealth Games
commonwealth games
Life and Style
Slim pickings: Spanx premium denim collection
fashionBillionaire founder of Spanx launches range of jeans that offers 'thigh-trimming construction'
News
Sabina Altynbekova has said she wants to be famous for playing volleyball, not her looks
people
News
i100
Life and Style
tech'World's first man-made leaves' could use photosynthesis to help astronauts breathe
Independent
Travel Shop
the manor
Up to 70% off luxury travel
on city breaks Find out more
santorini
Up to 70% off luxury travel
on chic beach resorts Find out more
sardina foodie
Up to 70% off luxury travel
on country retreats Find out more
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

SAP Project Manager

competitive: Progressive Recruitment: SAP PROJECT MANAGER - 3 MONTHS - BERKSHI...

SAP Project Manager

competitive: Progressive Recruitment: SAP PROJECT MANAGER - 3 MONTHS - BERKSHI...

Senior Investment Accounting Change Manager

£600 - £700 per day + competitive: Orgtel: Senior Investment Accounting Change...

Microsoft Dynamics AX Functional Consultant

£65000 - £75000 per annum + benefits: Progressive Recruitment: A rare opportun...

Day In a Page

Save the tiger: The day America’s love of backyard tigers led to a horrific bloodbath

The day America’s love of backyard tigers led to a horrific bloodbath

With only six per cent of the US population of these amazing big cats held in zoos, the Zanesville incident in 2011 was inevitable
Samuel Beckett's biographer reveals secrets of the writer's time as a French Resistance spy

How Samuel Beckett became a French Resistance spy

As this year's Samuel Beckett festival opens in Enniskillen, James Knowlson, recalls how the Irish writer risked his life for liberty and narrowly escaped capture by the Gestapo
Star Wars Episode VII is being shot on film - and now Kodak is launching a last-ditch bid to keep celluloid alive

Kodak's last-ditch bid to keep celluloid alive

Director J J Abrams and a few digital refuseniks shoot movies on film. Simon Usborne wonders what the fuss is about
Once stilted and melodramatic, Hollywood is giving acting in video games a makeover

Acting in video games gets a makeover

David Crookes meets two of the genre's most popular voices
Could our smartphones soon be diagnosing diseases via Health Kit and Google Fit?

Could smartphones soon be diagnosing diseases?

Health Kit and Google Fit have been described as "the beginning of a health revolution"
Ryanair has turned on the 'charm offensive' but can we learn to love the cut-price carrier again?

Can we learn to love Ryanair again?

Four recent travellers give their verdicts on the carrier's improved customer service
Billionaire founder of Spanx launches range of jeans that offers

Spanx launches range of jeans

The jeans come in two styles, multiple cuts and three washes and will go on sale in the UK in October
10 best over-ear headphones

Aural pleasure: 10 best over-ear headphones

Listen to your favourite tracks with this selection, offering everything from lambskin earmuffs to stainless steel
Commonwealth Games 2014: David Millar ready to serve up gold for his beloved Scotland in the end

Commonwealth Games

David Millar ready to serve up gold for his beloved Scotland in the end
UCI Mountain Bike World Cup 2014: Downhill all the way to the top for the Atherton siblings

UCI Mountain Bike World Cup

Downhill all the way to the top for the Atherton siblings
Save the tiger: The animals bred for bones on China’s tiger farms

The animals bred for bones on China’s tiger farms

The big cats kept in captivity to perform for paying audiences and then, when dead, their bodies used to fortify wine
A former custard factory, a Midlands bog and a Leeds cemetery all included in top 50 hidden spots in the UK

A former custard factory, a Midlands bog and a Leeds cemetery

Introducing the top 50 hidden spots in Britain
Ebola epidemic: Plagued by fear

Ebola epidemic: Plagued by fear

How a disease that has claimed fewer than 2,000 victims in its history has earned a place in the darkest corner of the public's imagination
Chris Pratt: From 'Parks and Recreation' to 'Guardians of the Galaxy'

From 'Parks and Recreation' to 'Guardians of the Galaxy'

He was homeless in Hawaii when he got his big break. Now the comic actor Chris Pratt is Hollywood's new favourite action star
How live cinema screenings can boost arts audiences

How live cinema screenings can boost arts audiences

Broadcasting plays and exhibitions to cinemas is a sure-fire box office smash