In the 1980 bestseller, Cosmos, astronomer Carl Sagan famously wrote that there are more stars in the heavens than all the grains of sands covering the world's beaches. His apparent prescience was based, in part, on the premise that a hand full of sand contained approximately 10,000 separate grains. Sagan presented this estimate when astronomy's principal tools were still fixed very firmly to the Earth- it would be another decade before the Hubble Space telescope gave us a view of the heavens, undisturbed by the blurring effects of our atmosphere, that would enable scientists to make a more accurate calculation.

So, was Carl correct?

First, consider how many grains of sands cover the earth's beaches. Researchers at the University of Hawaii have actually taken a mathematical stab at this number by dividing the volume of an average sand grain by the volume of sand covering the Earth's shorelines. The volume of sand was obtained by multiplying the length of the world's beaches by their average width and depth. The number they calculated was seven quintillion five quadrillion (that's 7.5 followed by seventeen zeros or 7.5 billion billion) sand grains!

Next, consider how many stars fill the Universe. Well, if you were located at or very near the Earth's equator, you would be able to observe about 6,000 individual stars over the period of a year with unaided vision. Of course, there are far more than this visible with binoculars or a small telescope. But, the vast majority that can be seen through small optical instruments would be confined within our own Galaxy because the huge distance to even the nearest galactic neighbor makes spotting their individual stars almost impossible, even through the largest telescopes. So, the best way to count the total number of stars in the Universe is to reckon the population of stars in our own Galaxy and multiply that by the number of galaxies that exist throughout space.

To derive an estimate of the stars in our own galaxy, astronomers have to consider both the number of stars we can see at great distance and the number of fainter stars, such as dwarf stars, which are difficult to observe. Red dwarf stars, as an example, are believed to be the most numerous type of star but they are also very dim. It is also estimated that there are about 200 red dwarf stars for every Sun-like star. Anyway, by taking star counts in relatively small-sized samples of the sky, factoring for dwarf stars and extrapolating the apparent area encompassed by the samples, recent computations have placed the number of stars in the Milky Way at around 400 billion, plus or minus 200 billion- hey, what's a few billion between friends :>)

But, the Milky Way is just one galaxy. The Hubble Space Telescope is capable of detecting about 80 billion galaxies based on analysis of its pictures. For example, where ever the Hubble points, in all directions, thousands of never before seen galaxies are seen extending far into the distance.

So, if we assume that our Galaxy is more or less typical and use the lower estimate, 200 billion, for its total stellar population then multiply that by the number of galaxies within reach of the Hubble Space Telescope, researchers have concluded that there are at least 70 sextillion (that's 7 followed by twenty-two zeros or 70 thousand million million million) stars in the observable universe- this is the latest number as proposed in mid-2003.

To put it another way, there are 10 stars for every grain of sand, eleven times the number of cups of water in all the Earth's oceans, ten thousand times the number of wheat kernels that have ever been produced on Earth and ten billion times the number of cells in a human being!

This is a staggering number- and it's most likely a very, very low estimate because the number of galaxies filling the Universe is thought to be much larger than those the Hubble can see!

All of this is pertinent to the new image that depicts two star forming regions, both about 5,000 light years distant, in the direction of the constellation Sagittarius- looking towards the heart of our Galaxy.

The picture displays the Trifid Nebula, on the right, and on the left, M8, which is also known as the Lagoon. The picture is very wide; in fact you could fit several moons across its width. Between the two nebulae is a portion of the Milky Way's vast star clouds- most of the distant stars are about three times further away than the nebulae. An application used to prepare these images reported that this picture contains slightly over 29,000 individual stars, by the way!

Earth is not located near the center of our Galaxy- we are positioned about half-way to the edge of the Milky Way's flattened, spiral shape and therefore any view of the its central region is occluded by vast clouds of dust that hang along the spiral arms we must look through. Thus, a large proportion of the stars in this picture appear reddened. Many of the bright blue stars are newly formed, most likely, from the two nebulae seen in this image and are thus much closer to us.