For the final class the topic was Telescopes. We covered the history of telescopes and the different types. We were meant to go outside and use some telescopes, but due to the heavy Sydney rain this was not possible tonight. The advantage being we got to stay inside out of the cold and were able to ask Dr Payne more questions and learn more about astronomy, including about Edwin Hubble and the Hubble telescope, below:
Telescopes come in many different forms including optical, radio, microwave, infrared, ultraviolet and x-ray. Telescopes are all about extending the capability of the first astronomical detector: the naked eye. The light we capture from telescopes is vital for us to explore and understand the universe.
The telescope was developed in the 17th century and was a Flemish invention. One of the first people to turn the telescope towards the stars was Galileo and in his life he built many telescopes. He made many discoveries, including:
- The features of the moon such as valleys and craters
- Jupiter’s moons which meant not everything circled the Earth
- Many stars
- Phases of Venus
The Galilean moons of Jupiter are: Io, Europa, Ganymede and Callisto.
His most powerful telescope magnified by 33x, meaning everything he saw through it appeared 33x larger. The telescope also captured lots of light so objects through the telescope appeared brighter. He was able to see 10x as many stars than were visible to the naked eye. Brightness is the most important feature of a telescope, not the magnifying power but the brightness.
Galileo built a refractor style of telescope which used lenses, but the problem with this style is that objects appear fuzzy. This problem is called chromatic aberration. This problem was solved by Isaac Newton. Instead of a lens he used a curved mirror and this corrected the fuzziness caused by the lens. This style of telescope is called a Newtonian. All large contemporary telescopes have mirrors as the main optical component. Newton’s original mirror was 2.5 cm in diameter, today they reach 10 m in diameter.
This type of telescope is better if it is longer, objects appear closer and with more detail. The function of the objective lens is to form an image close to the opposite end of the tube. The distance from the objective lens to the image is called the focal length. The longer the focal length the larger the image produced. The function of the eyepiece is to enable the eye of the observer to have a closer look at the image. It is like a small magnifying glass. The more powerful, the more the telescope will magnify. The magnification of a telescope is equal to the focal length of the objective divided by the focal length of the eyepiece. For amateurs 40 to 150 is standard.
A curved mirror replaces the objective lens. The primary mirror produces an image at its focal length and an eyepiece is used to examine that image. The observer looks into the side of the tube, thanks to the small secondary mirror. Most amateurs use reflecting telescopes. The larger the primary mirror the more light the telescope captured and the brighter the image through the eyepiece. Double the size of a telescope and the light collecting power increases by 4.
The diameter of a telescope matters more than magnification. About 15 cm is a good size to start with. A Newtonian is preferred as you can buy a larger telescope for the same price as a small refractor style telescope. A Newtonian will reveal nebulae that will not appear in the refractor for the same price.
Another type of reflecting telescope is the cassegrain, and they give a superior image to the Newtonian. They have a longer focal length and a completely enclosed tube.
A good mount for your telescope is vital. A good mount is needed to help focus the lens and keep the telescope still. The example below is a Newtonian telescope on an equatorial mount.
The mount has 2 axes of rotation and can be fitted with an automatic tracking device.
What can you see?
We are limited by the type of telescope we have and the atmosphere of the Earth. Light pollution is also a problem for city and town dwellers. It is best to take your telescope into the country to view many stars, Jupiter and Saturn. Depending on the size of the telescope, 20cm will ensure you can see the great red spot of Jupiter and the separation of the rings of Saturn. A 20cm reflector will also let you see Uranus, Neptune, but to see Pluto a 40cm instrument at least is required. With a 10cm reflector bright nebulae will be visible, but as wispy blue clouds.
The biggest radio telescope is currently being built in China at 500m in diameter. The next largest is the Aricebo in Puerto Rico and is 305m across.
A radio telescope is like a giant ear listening for radio waves from space. Radio waves are a type of electromagnetic radiation similar to light. These signals are very weak, so the larger the telescope the more chance you have of picking up signals.
This telescope will search for ancient signals of hydrogen, one of the building blocks of the early universe. It will also hunt for new stars, and in particular pulsars, rapidly rotating stars.
The dish is made from 4,500 triangular panels that have been carefully lowered into place. Each panel can be adjusted so the telescope can be moved to view different parts of the sky.
Read more about this amazing telescope here: http://www.bbc.co.uk/news/resources/idt-0192822d-14f1-432b-bd25-92eab6466362
The universe began with the big bang and astronomers are building more advanced machines to look further and further back into the past to see what the conditions were like when this happened. One of the main questions to answer is “What is the mean density of the universe?” This will determine how much gravity there is and the eventual fate of the universe. Will the universe keep expanding or will it eventually collapse?
Astronomers are slaves to light and we know that we can only observe about 10% of light from the universe. Or, actually that the universe only gives us 10% of its light. We can’t see dare energy and arm matter. It is thought that 68% of the universe is made from dark energy and 27% is dark matter. We know something is there because of the gravitational influence it has over nearby objects. Everything we know about the universe makes up about 5% of it.
More about dark energy and dark matter in another blog.
This was the final class and the whole course was amazing! Huge thanks go to Dr Paul Payne for his amazing lessons, 3D presentations and humour. Huge thanks also to everyone at Sydney Observatory for putting the course on. I will be back for more astronomy later in the year.
Here is a link to sign up for the next instalment of this course: https://maas.museum/event/astronomy-course-exploring-the-heavens/
Here is a link to Paul’s website: http://relativity.net.au/courses/