Physics trip: GREENWICH

Physics trip: GREENWICH

How many stars are there in the sky?
What is a star made of?
How far is it from the Sun to the Earth?

On 21st November, with the guidance of MPW Physics tutors, all A2 students studying Physics kept these questions in their mind as they went on a field trip to Greenwich Observatory to discover facts about the universe.

We started our exploration with the Peter Harrison Planetarium. Amazing images collected from telescopes and satellites are projected to a fully immersive dome, creating a vivid and enjoyable ‘trip’ above the sky. Our ancestors used their imagination to join stars in particular shapes and so the twelve constellations of the zodiac are familiar to us. How about other, anonymous, stars? We know that our Earth is in the solar system, which is a small part of the Milky Way galaxy and one galaxy is just like a drop of water inside endless sea. The number of stars and planets in the universe is much greater than the sum of grains and sands on the Earth, or the total number of heartbeats of all the human beings who have ever existed, according to the astronomer who talked us through our visit to the planetarium.

We also found out that the knowledge taught in class is closely related to the research and applications of physics in astronomy. The chemical elements present in a star can be revealed by reading its spectrum, a topic introduced in AS Physics. As in a rainbow, a spectrum reveals the different wavelengths present in white light as different colours. Each chemical element absorbs certain wavelengths and this is indicated by dark lines in the spectrum. Astronomers compare those dark lines with data to confirm the elements present in a star. More interestingly, we can tell if an object in space is towards or away from us by using spectroscopy. As our guide explained, if the dark lines have shifted to the red end of the spectrum, the object is moving away. A blue shift of the dark lines means that the object is coming towards us.

Finally, we finished our trip by learning not only how to identify galaxies, but also what Hubble’s Law is and how to make applications of it. We still recall how we struggled in plotting Hubble Diagrams, as the calculations were really tricky, involving huge numbers. However, through working together, every team produced a quite reasonable graph to prove that the velocity of a galaxy is proportional to its distance from the observer.