But what exactly was it that fuelled his deep sense of paranoia and dread at the scale of the cosmos, and made his work so memorable?

H. P. Lovecraft was born in August 1890 and died in March 1937. (And I have just experienced a queasy moment of realization: that I am now older than he was when he died.) He's remembered to this day mostly as an author of disturbing and fantastic fiction, and as the spark that ignited an entire sub-genre of horror, in which many other authors work (myself included).

We know that Lovecraft was fascinated by astronomy as a boy; and the formative years for this interest would have been approximately 1895-1910.

A trip to the McCormick Museum at the University of Virginia's online history of photographic astronomy may shed some light on Lovecraft's view of the cosmos. Prior to the development of photographic processes, astronomy was limited to what the human eye could see, with or without magnification. But from the 1840s onwards astronomers began to experiment with Daguerreotypes and later with improved photographic processes. By use of long exposure times, and telescopes on mobile platforms that kept the instruments aimed at the same point in the heavens despite the Earth's rotation, it was possible to gather far more photons than a merely human eye could sense, over a longer period of time, from fainter objects. During the 1880s the use of silver bromide emulsions revolutionized the field of photographic astronomy, and permitted the first photographic sky surveys.

(Incidentally, there's a lot more on the history of photographic astronomy and astronometry here—it's well worth a browse.)

Prior to the 1890s, our conception of the universe was very different from the cosmology we are familiar with today.

We measure the Apparent magnitude of an object to classify stars by how bright they appear to the naked eye, using a system dating to antiquity but formalized in the 1850s. (The higher the number, the fainter the object: anything with an apparent magnitude higher than roughly 6.5 is not visible to the naked eye.) There are roughly 5000 stars in the skies that are visible with the naked eye, and a scant double-handful of visible galaxies. Individual stars in other galaxies are not visible to the naked eye, and so these objects were commonly known as "spiral nebulae", to distinguish them from other non-stellar objects (which today are known to be gas and dust clouds). When we add telescopic assistance, many more stars are visible: there are about a third of a million above apparent magnitude 10.0.

So the universe into which H. P. Lovecraft was born consisted of the Milky Way, containing perhaps a million stars, and some irritating unidentifiable nebulous things.

But there's more! Remember that in 1890 we didn't know how the sun generated heat and light, or how old it was. Perhaps the best-remembered theory of the time was Lord Kelvin's paper from 1862: "the sun is now an incandescent liquid mass, radiating away heat, either primitively created in his substance, or, what seems far more probable, generated by the falling in of meteors in past times, with no sensible compensation by a continuance of meteoric action." Working backwards from this assumption, Lord Kelvin derived an estimate of the maximum age of the sun:

We may, therefore, accept, as a lowest estimate for the sun's initial heat, 10,000,000 times a year's supply at the present rate, but 50,000,000 or 100,000,000 as possible, in consequence of the sun's greater density in his central parts. The considerations adduced above, in this paper, regarding the sun's possible specific heat, rate of cooling, and superficial temperature, render it probable that he must have been very sensibly warmer one million years ago than now; and, consequently, if he has existed as a luminary for ten or twenty million years, he must have radiated away considerably more than the corresponding number of times the present yearly amount of loss. It seems, therefore, on the whole most probable that the sun has not illuminated the earth for 100,000,000 years, and almost certain that he has not done so for 500,000,000 years. As for the future, we may say, with equal certainty, that inhabitants of the earth can not continue to enjoy the light and heat essential to their life for many million years longer unless sources now unknown to us are prepared in the great storehouse of creation.

Remember, if you will, that the discovery of radioactivity did not take place until 1896. Lord Kelvin's speculation was based on the rigorously understood physics of the Newtonian era; working with the best information available, he placed the age of the sun at most likely less than 100 million years (and definitely less than 500 million).

So: the universe H. P. Lovecraft was born into consisted of a single galaxy containing about a million stars, and our own star was less than 100 million years old.

The universe Lovecraft died in was very different.

The first attempts at using parallax to determine the distance of stars and other astronomical objects from photographs took place in the 1890s. Instruments for comparing photographic plates taken at different times during the Earth's orbit around the sun were developed over the next couple of decades, and studies soon expanded from measurements of distance to proper motion and spectral analysis. At the same time, larger and larger mirrors were becoming available for reflector telescopes, aiding the observation of increasingly distant (and faint) objects. During the second decade of the 20th century, Edwin Hubble pushed back the distance scale of the observable universe to a dizzying extent. By studying Cepheid variables, a type of star characterised by its highly predictable variable luminosity (making them a useful standard candle), and comparing the brightness of Cepheid variables visible in "spiral nebulae" to nearer Cepheids whose distance could be calculated by parallax observation, Hubble was able to prove that the spiral nebulae were located far outside the milky way. Next, during the 1920s, Hubble used spectroscopic observation and distance estimates based on Cepheid variables to establish that more distant galaxies were receding faster, determining the Hubble constant—the rate at which the observable universe is expanding.

Finally, during the early decades of the 20th century it became obvious that the sun's radiation was powered not by gravitational collapse but by some other nuclear-related energy source. The precise mechanism was not determined until the 1940s, but in 1920 Arthur Eddington proposed that the fusion of hydrogen nuclei into helium was a likely candidate; subsequently the detailed theory of stellar nucleosynthesis emerged to support this hypothesis.

Today, in 2013, we live in the Milky Way galaxy; it is believed to contain between 100 billion and 500 billion stars. The Milky Way is part of a local group of over fifty galaxies, but the observable universe is believed to contain 100-200 billion galaxies (and possibly a lot more). Finally, detailed observations have determined that our universe is 13.8 billion years old.

At the time of Lovecraft's death in 1937, the universe was considerably smaller—but it was still vastly larger than it had been at the time of his birth; with over a hundred million stars in our own galaxy, and many tens or hundreds of millions of other galaxies estimated, and the upper limit on the sun's age raised to five billion years, the universe had expanded by two orders of magnitude in age and nine orders of magnitude in size (as measured by the number of stars) during Lovecraft's life. That's eleven orders of magnitude in just over four decades.

Let's look for a modern metaphor:

The cosmos expanded during Lovecraft's life at a rate comparable to the rate of expansion of available data storage during my life. I was born in late 1964. In 1973, the total manufactured fixed disk storage capacity in the United States was on the order of 100Gb. 40 years later, it's really hard to buy hard disks that small; hard disk storage currently costs on the order of 4 cents per gigabyte, giving our 1973 USA's installed hard disk capacity a value of around $5.

I am going to take it as so glaringly obvious that our computers' power has grown exponentially since 1973 that I'm not going to bother with figures, other than to note that my mobile phone in 2013 has over a thousand times the processing power, storage/memory bandwidth, and storage capacity of a Cray-1 supercomputer from 1976 (price: $8.86 million, in 1976 dollars—$36.46M in today's money.

Forty years of Moore's law and its cousins have given us an inflating, exponentiating bubble in computing power that compares eerily to the forty year marathon of cosmological discoveries that informed Lovecraft's later weltanshauung, as expressed through fictions such as "At the Mountains of Madness" (1931), "The Color out of Space" (1927) and "The Whisperer in Darkness" (1931).

I believe that Lovecraft's sense of cosmological dread emerged from the exponential expansion and recomplication of the universe he lived in—it eerily prefigures the appeal of today's singularitarian fiction, which depends for its dizzying affect on a similar exponential growth curve. Lovecraft interpreted the expansion of his universe as a thing of horror, a changing cosmic scale factor that ground humanity down into insignificance. Not all writers from his period took this approach; to many, the expanded universe was a playground of joyous imagination. Today, singularitarian fiction is frequently aspirational, a literature of transcendence (with theological taproots linking it to the early Russian cosmists). But the inversion of a sense of wonder is a sense of dread. Which leaves me asking, where is the singularitarian Lovecraft?