When Chris Robinson explained to his stepdaughters he was travelling around the moon, they believed their stepfather was preparing for an adventure in space.

As he rose early to log hours on a bicycle and undertake miles of rowing, little Abbie and Chloe thought he was training to become an astronaut.

The 38-year-old Aberdonian's lunar adventure may have captured his stepdaughters' imagination but his feet will remain firmly on the ground when he attempts to travel the circumference of the moon by the end of the year with colleague Sean Gordon.

"They think I'm physically going up there and walking round it so it was quite funny that way," he says.

Walking, rowing, swimming and cycling, the two businessmen travel up to 40km each day in the gym and the great outdoors to reach the 10,921km it takes to travel around the moon.

Their challenge began over a coffee following a networking event in Aberdeen.

Having met a medical consultation company and then a charity, the pair joked they could travel one million metres, a distance of 10,000km, for a good cause.

Yet their challenge failed to hit home the enormity of the task they were about to undertake.

Online searches for distances from their homes in Aberdeen to far-reaching places did not strike a chord until one of them stumbled upon the circumference of the moon.

With an extra 921km to add to their astronomical challenge, the pair became the "Moon Men" and vowed to travel the circumference of the moon by December 31 in aid of local charity Charlie House.

They are aiming to raise an ambitious £100,000 for the organisation, which supports children with complex disabilities and life-limiting conditions through short breaks, activities and practical and emotional support.

"It has [helped people resonate with the challenge] because of the distance," explains Chris.

"A lot of people still don't understand what 10,921 is in kilometres, they don't really understand the magnitude of it but when you say it's the moon they kind of cotton on that it's a long distance we're doing."

"It sounded exciting, the idea of getting to a certain distance within a certain period of time, it was a big target we wanted to set and it didn't take much to say let's do it," adds 25-year-old Sean.

"It's quite an interesting concept behind it, no-one that I know of has ever done it so I said let's go ahead and do it."

Chris explains the work Charlie House does resonated with him on a personal level.

His wife Suzie had helped raise £9000 so that one of their friend's children could enjoy a day out at the park.

"In our village, there's no access to disabled parks so they wanted to raise money to put a wheelchair swing into the park," he says.

"So it was kind of stemmed off that as well because Charlie House [helps] kids with life-limiting illness and we've a bit of a personal connection from that side because of our friend's son."

Dr. Sorcha Hume from Charlie House says: "The Moon Challenge is certainly one of the quirkiest and challenging we have seen and we wish Chris and Sean all the best in reaching their fundraising target for Charlie House.

"The funds raised will go towards expanding our current projects, such as our many clubs and activities and community team.

"A huge thank you to our Moon Men for their efforts, we hope the local community will get behind them."

While Sean has experience in running marathons, Chris says his only exercise up until recently was walking.

The demanding task at hand meant he required expert help to build up his fitness and ensure he did not injure himself.

Working with Temple Medical, the company offered the pair advice on nutrition and how to avoid injury as they built up their fitness, burning some 1000 calories through exercise alone.

Their office gym also provided a personal trainer to break down the distances into manageable targets, starting with 280km each week and working towards 620km in the final stretch of the challenge.

For Sean, who says he competes in six or seven running events a year, having the mental strength to get through the challenge has been harder than the physical distance.

He has pushed himself a little far at times, though.

"There was one weekend where I ended up cycling from my house to Montrose and back, I didn't mean to do that it just sort of happened.

"I decided to keep going one day and when I got to Montrose I thought, I need to cycle back now," he laughs.

Chris is delighted they are 300km ahead of schedule and are on track to meet their target.

He says he hopes it is completed before Christmas.

While his wobbly legs have subsided with time, with four months left to go Chris says he is feeling fitter than ever and believes the "Moon Men" challenge has changed him for the better.

"Without a doubt [it has changed my life]," he says.

"It was a bit of daunting task when i first looked at it but now I'm kind of in the routine of getting to the gym at 6am and I'm there until 8am, doing 40k or 50k between running and cycling and cross trainer and rowing but I'm in there every morning."

While his step-daughters may be a little confused when it comes to their astronaut stepfather's goals, their support is out of this world.

"They are quite supportive and when I get home after a long day of cycling I can hardly move my legs so they bring me my coffee so I'm quite happy," he laughs.