# Can Santa Claus see your house from his sleigh?

Millions of children across the world will be looking up at the night sky on Christmas Eve to get a glimpse of Santa Claus and his reindeer – but what if he could see your house from the sky?

Students at the University of Leicester may have found the answer, after calculating that in order for a house to be seen from space at Christmas it will need to be covered in more than 2,600 fairy lights.

As part of their physics degrees, four Leicester students (aka Santa’s Little Helpers) calculated the number of Christmas lights required to make a house visible from the orbit of the International Space Station (ISS), which is approximately 400km high.

Using equations and principles learned on their course, and taking into account the limitations of the human eye, the students estimated that the luminosity of a Christmas display would need to be 10.6 x 103 lumens in order to be visible from 400km away. A single LED Christmas light has a luminosity of about four lumens, meaning that at least 2,638 lights would be required for the ISS astronauts to make out an individual house.

The students drew their inspiration from the 2006 movie Deck the Halls, in which a character played by Danny DeVito attempts to make his house visible from space.

The International Space Station will pass over the UK twice on Christmas morning, according to timings released by NASA. If skies are clear, it will be visible as a moving point of light for two minutes from 5.19am and again for four minutes from 6.53am. Six crew members will be spending Christmas aboard the ISS.

The paper by R Bradley-Evans, R Gafur, R Heath and M Hough was published in the University’s Journal of Physics Special Topics. This in-house journal enables students to learn about the process of peer review by writing and reviewing papers by applying theoretical concepts to light-hearted ideas.

When the ISS travels across the sky on Christmas morning, many parents will point it out to sleepy children and tell them it is Santa Claus’ sleigh.

A spokesperson for the University of Leicester said: “We would like to assure everyone that Santa Claus does not need 2,638 lights to find a house, as he is magic and already knows where all good children live.”