Leading astrophysicist for Dublin lecture

HUMANS LIKE TO measure things no matter how difficult the challenge. The metre measure was originally defined by the French by measuring the distance from the equator to the North Pole through Paris.

How much greater the challenge therefore to attempt to measure the universe, working from a starting point sitting here on the edge of a galaxy far from the centre of things?

Yet most of what we know about the universe comes from measuring distances across space, explains Prof Michael Rowan-Robinson, the professor of astrophysics at Imperial College London.

Prof Rowan-Robinson will describe these efforts in a public lecture next Monday at Trinity College Dublin in a lecture, The Cosmological Distance - the key to understanding the universe, which describes how measuring distance in space taught us much about the birth and structure of the universe. "I want to show the current picture of our understanding of what the universe is, by doing so from this unusual angle," Prof Rowan-Robinson says. "It is all about measurement of distance."

He will be speaking on the subject with some authority. He led Imperial College's astrophysics group from 1993 to 2007 and was also president of the Royal Astronomical Society from 2006 through 2008.

The French defined the metre by measuring the girth of the earth and others quickly turned their attentions towards gauging the distance to the moon.

Early efforts to measure cosmological distances arose when galaxies were detected using large telescopes. Astronomers learned to use Cepheid stars, whose brightness varies over time, as a measure of distance, Prof Rowan-Robinson explained.

The bright stellar explosions called supernovas provided yet another way to tease out questions of distance. And the measurement of a star's "red shift", the change in a star's light spectrum towards longer wavelengths caused by its motion away from us, offers a powerful method for measuring distance.

"It tells us something about the geometry of the universe," Prof Rowan-Robinson says, something that can deliver surprises. "Unexpectedly, we live in a universe where gravity works in a different way."

Gravity attracts over moderate distances but when looking at the universe, it seems to be a repelling force. "This force is attributed to something called dark energy. The evidence for it comes from measuring distances."

Astronomers now calculate that only 4 per cent of our total universe is made up of things we can see. Another 21 per cent is so called dark matter and the remaining 75 per cent is dark energy. Prof Rowan-Robinson's talk will be visually striking with images from the Hubble Space Telescope and other sources.

The talk will take place at 8pm in the Schrodinger Theatre in the Physics Building, Trinity College Dublin. Tickets cost €7 and €5 for Astronomy Ireland members, students and over 65s. Tickets may be booked at www.astronomy.ie or by phone on 01-8470777.