The Hubble Key Project: 25 years in space

A reblogging of something I wrote for Yale UP about the Hubble Telescope:

The True Mission of the Hubble Telescope

John Gribbin

When I started out in astronomy, the Big Bang theory was just becoming accepted as a good description of the Universe in which we live. But there was one big problem with it. Nobody knew how old the Universe was.

The age of the Universe is related to how fast it is expanding. If it started out small and hot (in the Big Bang), then to get to its present state obviously takes less time if it is expanding quickly than if it is expanding slowly. This key expansion rate is worked out by measuring redshifts of distant galaxies, which tell us how fast they are receding from us, and comparing these with their distances. Combining the two measurements makes it possible to infer how long ago the expansion began. Measuring redshifts is straightforward and gives unambiguous results, although it requires great technical skill. But measuring distances was the problem.

Astronomers measure distances by comparing the apparent brightnesses of different objects which are known to have the same intrinsic brightness. These are known as “standard candles.” This is like measuring the distance to a 100-watt light by measuring how bright (or rather, how faint) it seems to be.

The favoured standard candles used by astronomers are a family of stars known as Cepheids, which brighten and fade in a regular way that is related to their intrinsic brightness. But observations of Cepheids in distant galaxies are very difficult, because of the obscuring effects of dust in space, the varying influence of the Earth’s atmosphere, and so on. As a result, estimates of the expansion rate varied widely in the years before the Hubble Telescope was launched. This rate is measured in terms of a number called the Hubble Parameter, H, and due to a wide range of estimates for H, estimates of the age of the Universe ranged from 8 billion to 16 billion years.

To resolve the puzzle, a study know as the Hubble Key Project was planned. This was the primary raison d’être for the telescope—to measure the Hubble Parameter (and therefore the age of the Universe) accurately (within 10 per cent) by using the Hubble Telescope to study Cepheid stars in  distant galaxies.

Although the Hubble team waited to gather all their data in one package before analysing it to produce an accurate measurement of H, they generously provided other astronomers with some of the Cepheid measurements as they went along. As a result, with my colleagues Simon Goodwin and Martin Hendry at Sussex University I was able to use their measurements in a more rough and ready approximate method, finding that the Hubble Parameter must be at the low end of the previously accepted range and that the age of the Universe is a little over 13 billion years; but we did not meet the “within ten per cent” criterion (see http://arxiv.org/abs/astro-ph/9704289v1). Just after we came up with our value, in 2001 the Hubble team itself presented their final analysis, inferring an age of 14 million years plus or minus that promised 10 per cent. The team rightly received the  2009 Cosmology Prize of the Peter and Patricia Gruber Foundation, worth $500,000, for their work. Since then, other studies have pinned down the age of the Universe down even more precisely, to 13.8 billion years. This is one of the most profound results in all of science.  Everything else the Hubble Telescope has produced, including the stunning pictures of galaxies which made it a household name, is merely the icing on the cake.


John Gribbin is a Visiting Fellow in Astronomy at the University of Sussex and the author of many books including The Birth of Time, The Origins of the Future, Almost Everyone’s Guide to Science, and Stardust. Find more at his website and blog.


Further Reading:

The Birth of Time Cover

Our Future in Space?

Here is the unedited version of my latest WSJ review.  As ever, the “Mr” is their house style:

Beyond: Our Future in Space

Chris Impey

Chris Impey is an optimist. His glass is at least three-quarters full, and he sees an extended and glorious future for humankind in space. I confess that I do not agree with him (although there was a time when I shared this view), but he has written an entertaining and informative book making as strong a case as it is possible to make that I, and those who think like me, are wrong. He has also produced one of the most accessible accounts of the history of rockets and space travel, well worth the price of admission whatever your views about our future in space.

The theme is set by a brief opening chapter in which Mr Impey explores the human restlessness that drove us out of Africa and across the world. This outward urge, he argues, must in due time (not very much due time) take us off the planet. As he explains later in the book, there is genetic evidence that the human population was reduced to no more than two thousand people by some catastrophic event (perhaps the explosion of a supervolcano in Indonesia) some time more than 60,000 years ago. As a result there is less genetic variety – less variation in the DNA — among the entire seven billion of us alive today than there is among the members of a single band of a few dozen chimpanzees. So any genetic predisposition to move on over the horizon among those two thousand would have spread among their descendants. Not that those descendants would have set out with the idea of crossing the globe; rather, if in each generation of an expanding population a few individuals moved over the next hill to get away from the neighbours, it would have taken less than 60,000 years for people to spread all the way to Europe, Asia, and across the land bridge where the Bering Strait now is into the Americas.

Is it the same urge that led pioneers such as Konstantin Tsiolkovsky and Wernher von Braun to develop rockets? Von Braun always claimed to be apolitical and solely interested in getting in to space; but Mr Impey accurately recalls his willingness to dress up in uniform, join the Nazi Party, and turn a blind eye to the slave labour used in striving for that end. Mr Impey also, though, makes one howler which for personal reasons I cannot ignore. He describes V2 rockets “screaming out of the sky at four times the speed of sound”. At that speed, of course, the rockets arrived silently, followed by the sound; my grandparents recalled to me that the real terror of these weapons was that they exploded without any warning.

There are a couple of other slips worth mentioning. The claim that the Viking probes of the mid-1970s carried out the “first and only” tests for life in the Martian soil ignores the landers currently on the surface of the red planet, and hydrogen, not helium, is the lightest gas. These are quibbles. But a greater lack of understanding of the background to the space age is provided by the author’s surprise that President Eisenhower should have warned of the dangers of “the military-industrial complex” having too great an influence on developing space technology. “It’s ironic that this five-star general and two-term president”, says Mr Impey, “issued such a clarion call against concentration of influence within and around the government.” On the contrary! President Eisenhower was exactly the right man in the right place, and with the right experience, to make such a warning. The result was a civilian agency, NASA, that took the lead in the American space effort.

Fascinating though the history is, the meat of this book concerns present day developments, in which private enterprise is beginning to take over from national and international agencies such as NASA and ESA, and the projection of this trend into the future. Private enterprise is certainly needed. It is embarrassing enough for Americans to know that until very recently launching astronauts and supplies to the International Space Station entirely depended on Russian technology and Russian goodwill; but it is positively frightening to realise how old that Soviet-era technology is. The rockets are essentially the same as the one that fired Yuri Gagarin in to orbit in the 1950s. Would you drive a 1950s car? One Russian engineer is quoted here as saying that updating this technology is like trying to upgrade a steam engine. “You equip it with a computer . . . You equip it with air conditioning. You put a locomotive driver with a university degree in the cabin, and it will still be the same stream locomotive.” But just recently a few supply trips to the ISS have been made by private companies hired by NASA. Surely the shape of things to come.

Beyond sketches the stories and personalities of the entrepreneurs involved in these developments — Burt Rutan, Richard Branson, Peter Diamandis, and Elon Musk. Their visions range from sub-orbital space hops to colonies on Mars founded by volunteers with a one-way ticket. All this is certainly achievable using developments of present-day technology, with bigger question marks concerning the ability of human beings to cope with the physical and mental problems of long space voyages. But Mr Impey looks beyond to future developments such as the idea of a “space elevator”, a cable stretching from the surface of the Earth out into space to connect with a space station in geostationary orbit. He also contemplates the vast number of planets now known to exist in our neighbourhood of the Milky Way and the possibility of travelling to them.

Aware that this sounds like science fiction, he has broken up his book with fictional vignettes between each section, describing the experiences of an astronaut training for and then departing on a voyage to the stars. Usually, I hate these gratuitous bits of (usually bad) fiction in non-fiction books. But for once, it works. Indeed, it works so well that I would like to see Mr Impey develop it into a full-blown book.

But perhaps this is because I am convinced that such a possibility really is fiction. The spaces and timescales involved are too great for me to take seriously the idea of people travelling to the stars. After all, there is, as Mr Impey also acknowledges, an alternative. Unmanned spaceprobes have been hugely successful in exploring the Solar System. Even now, one is orbiting a comet, another is in orbit around the dwarf planet Ceres, and a third is closing in on Pluto. It is very easy to see us developing the ability to send future probes to planets orbiting other stars, and to get back information from them. All of which raises the question, if it is easy, why has no other civilization done it? Why are there no alien spaceprobes signaling their presence to us? This is part of the puzzle of the Great Silence, suggesting that we may be alone in the Universe.

We may never resolve that puzzle, or at least, not for a long time. But Beyond sketches a timescale for the immediate future:

2035, a commercial space industry operating, with orbital flights frequent and affordable to the middle classes.

2045, colonies on the Moon and Mars.

2065, mining asteroids and the Moon.

2115, children born off-Earth and who have never been “home” come of age and agitate for self-government.

Ambitious and optimistic, and highly debatable. But on one point I am in full agreement with Mr Imney: “Space travel, however, will never be our top priority. There are poor people to feed, diseases to cure, wars to resolve, and a bruised planet to heal.”

John Gribbin is a visiting Fellow in astronomy at the University of Sussex

And author of

Alone in the Universe: Why our planet is unique (Wiley)