Hunting Uranus, the Solar System's Azure Ice Giant
This images shows a full, sunlit hemisphere of Uranus during NASA's Voyager 2 spacecraft flyby in 1986
The winter sky is by far the best time for astronomy. Long, dark nights with cool weather can present us with fabulously clear dark skies that last for hours. I've got some favorite winter astronomical targets coming up so hopefully they might inspire you to get out under the stars and hunt them down.
First up, Andromeda. Usually recognized as an autumn object, our most massive neighboring galaxy can still be seen in the west at around sunset. If you are in a dark location then you might be able to spot it with the naked eye. To find it, look out for the Great Square of the constellation Pegasus and locate the uppermost star which is generally regarded as the top left corner star and is known as Alpheratz.MORE: The Secret to Great Astronomical Photography
From here you should be able to see two fainter stars heading off away from the Square and from the second one, known as Mirach take a ‘right turn’ and hop up two more stars. In that general location you should scan with binoculars and look for a fuzzy blob, this is the Andromeda Galaxy. It is an object over 2 million light years away, which means the light you can see with your own eyes has been travelling for 2 million years -- in other words, you are looking back in time! A low magnification is the best way to observe the galaxy with a telescope and if you study it carefully you may be able to make out a hint of dark dust lanes.
Over to the east of the Square of Pegasus is the well-known constellation of Orion. If you can find this then you should be able to identify its famous three star belt (from east to west Alnitak, Alnilam and Mintaka) and from the central star, drop down an imaginary line to the horizon. You will see some fuzzy stars just below the belt and it is the central one which is of most interest.MORE: Getting to Grips With Your New Telescope
To the naked eye the Orion Nebula looks just like that, a faint fuzzy blob but turn a pair of binoculars onto the object and you will start to see some of the wispy filaments of nebulosity. The best views by far are seen through a low power telescope, the larger the aperture, the brighter the image you will see. Study the center of the nebulosity carefully and you will see the Trapezium cluster of stars, which are the hot young stars forming out of the vast cloud of gas and dust at a distance of just over 1,300 light years from us.
NASA, ESA and G. Bacon (STScI)
Sirius is a great star to observe, not only because it is nice and bright, but because it holds a real challenge for visual observers. Sirius, the "Dog Star," is a binary star with its fainter companion known as the "Pup" -- it is the difference in brightness that makes observing the Pup
challenging. You can find Sirius any time in the winter in the northern hemisphere by looking south. The brightest star you can see will be Sirius.10 Ways to Astronomically Astound Your Friends
You need good weather conditions and well-aligned telescope optics. To test your observing skills, try to split Rigel and its companion star, which is of comparable brightness making it easier to separate. Rigel is the white star at the bottom right of Orion so choose a high magnification and see if you can separate Rigel A and Rigel B, if you can, then you are in a good place to try to separate the Sirius binary. Wait for Sirius to be nice and high and give it a try.
This winter, Jupiter is nicely placed for observation in the night time sky on the border between the constellations Leo and Virgo. Lookout for a bright yellow/white star and that is the planet Jupiter.MORE: Bored With Astronomy? These 5 Projects Are For YOU
High powered binoculars might just be able to detect the four Galilean satellites, but a telescope will reveal them easily. Look at them over the period of one night to see how the moons move around the planet before turning your attention to the planet itself. Magnifications from 100x and above will reveal the many belts surrounding the planet and if the timing is right, the planet's Great Red Spot, which is a hurricane that has been raging for hundreds of years.
Rising behind Jupiter is the red planet Mars. Due to their orbital periods, Mars and Earth come particularly close every two years. This year's opposition (when Mars appears on the other side of the sky to the sun) is not the best but it will still be a better opposition than previous years. A telescope is needed to reveal any level of detail on the Martian disk, but the features can be greatly enhanced with careful use of red and orange filters. These filters will enhance the polar caps and darker surface features so while observing see if you can spot the caps or Syrtis Major, the large outcrop of dark rock.MORE: How to Communicate Our Sensational Universe
Amateur astronomers the world over enjoy regular views of Venus, Mars, Jupiter, Saturn and even elusive Mercury. The outer solar system planets Uranus and Neptune, however, are often overlooked.
Certainly they are fainter, as they are further away, so there is much less detail to be seen. That said, they are worthy targets and should be seen as a challenge and not avoided.
My personal interest in Uranus, which can be seen to the west in evening skies through December and January, started when I decided to have a bash at imaging it. To my surprise, it was easy enough to find and with a CCD plugged into the back of my telescope, easily revealed the planetary disk and four of its moons.
Uranus was discovered when 18th Century British astronomer William Herschel was engaged in the systematic study of stars in the night sky to identify double stars. For two years he studied the night sky almost every night and on March 13, 1781, he noticed a star in Taurus that seemed to appear a little different to the others.
As with all good astronomical observations Herschel studied the same object few nights later and noticed it had moved with respect to the background stars proving to Herschel that it was a new solar system object. He originally suspected it was a comet but later, its planetary nature was unveiled. Clearly a supporter of the monarchy, Herschel wanted to name the new planet Georgium Sidius after King George III but it was officially named Uranus, a Latinized version of the Greek god of the sky, Ourano.
The planet Herschel discovered increased the size of the known solar system to about 5.6 billion kilometers. Future observations revealed a world just over 50 thousand kilometers in diameter and gaseous in nature. Due to the presence of ices in its atmosphere such as ammonia and methane, Uranus is referred to as an "ice giant," differentiating itself from Jupiter and Saturn. The presence of methane leads to the absorption of red light and the reflection of blue light giving Uranus is stunning blue color.
The location of Uranus in the night sky.Mark Thompson
Throughout the remainder of January, Uranus can be found low in the west before sunset in the constellation Pisces (see above chart). It never shines fainter than 6th magnitude, which is the generally accepted limit of naked eye visibility from a dark site, but unless you are very keen sighted, binoculars are the best way to hunt it down. While it can be seen as a blue star through binoculars, higher magnification is needed to detect the planetary disk and, from my experience, a magnification of about 50 is needed. Visually you will only be able to see Uranus as a tiny blue disk but those of you with large telescopes, around 280mm can try CCD imaging with a black and white camera and a Wratten 25 filter.
If you want to pick out some of the planet’s twenty seven moons then the best chance you have visually is to hunt down Oberon and Titania. They are both around magnitude 14 so are right on the limit of a 300mm telescope but lie at a decent distance from the planet to make them easier to detect. The greater sensitivity of a CCD camera will greatly aid capturing images of the elusive moons.
For those observers with smaller instruments then the greatest interest can be gained by observing Uranus over the period of a few weeks to see its slow motion against the background of glittering stars.