Vesto Melvin Slipher was born on a farm in Indiana in 1875.
At the tender age of 26, after having completed a degree in mechanics and astronomy, he was offered a post at the Lowell observatory in Flagstaff. Slipher would be working as an assistant to Mr Lowell, the observatory's founder, who was using the telescope to look for signs of life on Mars. Mr Lowell offered Slipher the position for one year.
As it happened, Slipher left the Lowell observatory as observatory director 53 years later, and after having made one of the most important cosmological discoveries of the twenties century. A discovery that would have greatly helped Einstein.
In 1901 when Slipher started work at Lowell the general consensus amongst astronomers were that the universe was neither expanding nor contracting, but holding steady. A belief that lead to the expression 'The steady state universe'.
Slipher was not interested in discovering life on Mars. He wanted to know how far away objects travel through the universe and how such objects travel relative to Earth. To measure the movement of a galaxy Slipher used a spectrograph. An instrument, which splits the light from a distant object into individual colours.
Over the next 10 years Slipher perfected his understanding of the spectrograph output. He discovered that if a distant object was moving towards Earth the observed colours would be shifted towards the blue end of the spectrum. Likewise, if a distant galaxy was moving away from Earth the colours would be shifted towards the red end of the spectrum.
By 1912 Slipher had completed the analysis of four distant objects. Three of the spectrograph outputs were redshifted, while the last was blueshifted. Continuing his research, Slipher completed a further 12 observations in the next 24 months and found that all but one was redshifted.
(If you don't have sweaty palms after reading the last paragraph, read it again.)
Slipher's genius had within a short decade completely shattered the common belief that the universe was in a steady state, and had found concrete proof that the universe was expanding in all directions at great speed.
Slipher was not much of a 'salesman'. He hardly ever told anyone about his important work, or attended meetings with fellow scientists, or published scientific papers.
When Slipher finally left his beloved Lowell observatory in 1914 and presented his findings at a meeting of the American Astronomical Society, he received a long and deserved standing ovation from everyone there.
And now back to Einstein.
At the time Slipher was tucked away in his observatory and making one of the most profound cosmological discoveries, Einstein was putting the finishing touches to an equation, which described how space-time would develop over time.
To complete his equation Einstein needed to know if the universe was expanding, contracting or holding steady. Hence, he asked the world's leading astronomers what type of universe they believed to be in existence.
Had Slipher been a little quicker to get his findings out into the wider scientific community, and spend a little more time convincing other astronomers about the validity and significance of his observations, then perhaps Einstein would have received a different reply to the one he got in 1917: The universe was likely to be in a steady state.
The 'steady state' answer made Einstein reluctantly add the now famous cosmological constant to the final version of his equation. An action Einstein later described as 'The biggest blunder of my life'.
Slipher was by some margin the most important observational astronomer in the twenty century, but his genius was never really celebrated. Even to this day his name is largely unknown, though an obscure crater on the Moon and Mars carries his name.
Even Wikipedia's entry for Slipher is minuscule.