Andromeda Galaxy

20/20 Vision? How Far Can You See?

By Andy Fleming on | From andromedachild.com

M31, The Andromeda Galaxy, the furthest object we can see with our naked eyes, and the closest large galaxy to our own Milky Way (Credit: NASA/Robert Gendler)

ANDY FLEMING investigates the furthest object that we can see with our naked eyes You may be very surprised at what it is, and its distance from us!

Think that you’re doing well seeing the mountain range 50 miles away? Think again, the answer’s astronomical!

Reckon you’ve got good eyesight huh? Twenty-twenty vision right? So what’s the furthest you can see on a clear day?? A car registration plate at 30 yards? Ships ten miles out at sea on the horizon, or possibly a range of distant mountains 80 miles away.

Well, consider this: the furthest you can see with your unaided eyes is 1.475x10^19 or 1.475 multiplied by ten to the power nineteen miles or 14,750,000,000,000,000,000 miles followed by sixteen zeros (miles)! And you thought that the budget deficit was gargantuan! In astronomy, we only concern ourselves with miles when talking about ‘small’ distances, such as those between the inner rocky worlds of our own inner solar system. By the time we get to the gas giants and beyond its astronomical units or AU. One AU is 93,000,000 miles, the mean distance from the Earth to the Sun. Bring on interstellar distances, or indeed inter-galactic or inter-galactic group distances and we’re talking light years, the distance that light travels in one year.

The object we’re talking about here by the way while we digress into astronomical numbers is the Andromeda Galaxy, Messier object 31 or simply M31. It’s the nearest large galaxy to our own Milky May, and if you’re in the Northern Hemisphere it’s on display in a night sky near you now. Truth be told, you don’t have to worry too much about light pollution to see it either. Suburban skies will show it as a faint star while using averted vision in the constellation of Andromeda, the Princess.

How to locate the Andromeda Galaxy, M31

When we look at the night sky, we see every moon, planet, star and galaxy not as they are – but as they were. Your eyes are time machines – your binoculars and telescopes even more so. We view the ‘Andromeda Nebula’, which the great American astronomer Edwin Hubble realised was a galaxy or ‘island universe’ in its own right (and not a tenuous interstellar nebula of gas in our own galaxy), as it was 2.5 billion years ago, before homo sapiens first walked the Earth.

To find the Andromeda Galaxy, I firstly look for the constellation of Cassieopia, the great ‘W’ in northern hemisphere skies. It’s a circumpolar constellation in mid northern latitudes which means it’s visible throughout the year. Well below Cassieopia, and slightly to the right, in an area devoid of bright stars, you will see one lonesome bright orange star, the double star Mirach (Beta Andromeda). Star hop up and slightly right two faint stars (Mu and Nu Andromeda), and slightly to the right of Nu is a faint star like speck – that’s M31. But take a look at it through some common or garden 10x50 binoculars and you’re in for a jaw-dropping sight. What you see is a hazy ball of stars, the central bulge of this fabulous spiral galaxy.

Some more details are revealed with a telescope with a low power eyepiece, but to be quite honest I’ve always found M31 a disappointing telescope target – it’s definitely far better with binoculars due to their intrinsic larger field of view.

As you view our beautiful galactic neighbour, there is one final twist in this tale of cosmic distances. The Andromeda Galaxy is on the move – and quickly at 120 kilometres per second. And it’s coming towards us! In 3 or 4 billion years from now our own Milky Way and M31 will merge in a celestial show of galactic cannibalism. Will our solar system and the Earth survive?

The answer is quite academic really as our Sun is already getter hotter. Our planet will be uninhabitable 300 million years hence, and in any case by the time of the merger our Sun will have exhausted its supply of hydrogen fusion fuel and will be on the way to becoming a bloated red giant. The Earth will have long since been burned to a crisp.

So the next time someone asks you how far you can see on a clear day, surprise them with the only correct and astounding answer.