So much to see in the night sky
Humans have always looked into the night sky and marveled at the lights scattered across the celestial sphere. Every culture on our planet has sought an explanation for the stars we see. Ancient Greeks and Persians went so far as to study the sky making note of the unusual, such as the planets.
As civilization progressed and our instrumentation became more sophisticated, astronomers were able to discern the paths and patterns followed by the planets with more clarity.
Observations by Brahe, Kepler, Galileo and Copernicus led to the development of sun-centred or heliocentric view of the solar system.
As instrumentation improved and lenses became more sophisticated, astronomers were able to build better telescopes. Galileo was able to see the four major moons of Jupiter from which he was able to work out the size of the solar system and confirm the heliocentric model.
After all, if bodies could orbit Jupiter then surely the planets could orbit the sun. The older Ptolemaic model couldn’t explain the observations of Galileo and other astronomers.
But what kept everything going around? What kept the planets in their orbits? What allowed the heavens to be?
The answer is simple – gravity. It is the universal force holding planets to their suns and suns within galaxies and so on.
Isaac Newton was the first to formulate a law for gravity and calculus which allowed scientists to actually work everything out. Or almost everything. Gravity as a force of nature led physics to much of our modern understanding of the cosmos.
Astronomy has changed a lot over the past 300 years and by leaps and bounds over the last 30 years. Much of this is due to better instrumentation – to being able to see farther more clearly and at a host of different wavelengths.
With the discovery of the telescope, astronomers were able to examine all of the stars in the sky. They discovered the new planets Uranus (1781) and Neptune (1846) and the dwarf planet Pluto (1930). They were able to see moons around Mars, Saturn, and the other planets – 181 at last count.
We now have many space-based observatories which allow us to see well beyond our solar system and are helping to develop a deeper understanding of the universe.
The most famous is the Hubble Space Telescope which opened up the cosmos in a way which could not be achieved on the Earth’s surface at the time nor imagined by our ancestors as they gazed at the night sky.
Hubble’s deep field images have shown us a Universe filled with billions upon billions of galaxies and each is filled with untold billions of stars. The Universe is a crowded place.
But Hubble is not the only space observatory.
In 2009, NASA launched the Kepler Space Telescope with the very specific mission of detecting exoplanets – planets circling other stars.
We have long suspected other stars had their own solar systems but at interstellar distances, they are hard to see.
One method of detecting an exoplanet is to watch a star wobble. While planets are held in orbit by a star’s gravity, the gravity of a planet also pulls on the star. It is a bit like a pair of figure skaters in a spin. They orbit a mutual centre of gravity with each pulling on the other.
From our perspective, provided the plane of the orbit is oriented towards us, the planet appears to wobble to and fro. Careful observation can detect this wobble and this was the first method which confirmed the existence of exoplanets.
The Kepler Space Telescope used a different approach. As a planet passes between us and its star, it causes the light from the star to dim slightly.
This can be seen in our solar system when either Mercury or Venus pass between the Earth and the Sun.
Kepler keeps track of the light intensity of 145,000 main sequence stars similar to the Sun. Variations in intensities have led to the confirmed discover of 2,681 exoplanets with another 2,900 waiting for confirmation by independent measurements.
Not only is the universe filled with untold billions of stars but the number of planets is staggering. Present estimates suggest half the stars in our galaxy have planets orbiting them and there is no reason to think our galaxy is unique.
Astronomers have even found planets in the “Goldilocks Zone” where the conditions are neither too hot nor too cold for liquid water to occur so planets might have Earth-like climates.
Unfortunately, NASA announced this week the Kepler Space Telescope has run out of fuel and will cease its work. It is one instrument in the long history of astronomy but it has certainly made a major contribution. Other telescopes will now have to carry on the work.
And one day, we might finally find signs of intelligent life in the universe.