“Why do we need big telescopes?” was the question studied in the seminar I attended titled ‘Science with the world’s largest telescopes’ by Dr Katharine Johnston on 10th December.
Big optical telescopes provide 2 main benefits which the seminar outlined. Firstly, a larger diameter means the resolution of the image (the ability to distinguish two objects that are close together as separate so that we can see finer details) improves as resolution is proportional to the wavelength of light and the diameter of the scope. The sensitivity (the smallest signal a telescope or detector can reliably measure above noise) also increases with larger telescopes making it easier to detect very faint galaxies, stars or molecules.
Big radio telescopes also provide benefits as radio wavelengths are much longer than optical waves and the longer the wavelength, the larger the telescope needed to observe details. However, it is a lot of effort to make these big telescopes so why do we build them? The seminar discussed how radio telescopes are needed to solve a specific problem: Interstellar dust. Interstellar dust are big conglomerations of molecules, can obscure the universe as it blocks visible light as light gets absorbed or scattered by the dust. However, infrared and radio wavelengths can penetrate dust as they have longer wavelengths, which can reveal hidden stars and structures.
ALMA (Atacama Large Millimetre/submillimetre Array) is an example of a large telescope. It is made up of 66 antennas on the Chajnantor plateau in the Atacama Desert in Chile with an altitude of 5050m which act as one giant telescope. Signals from multiple antennas are combined. The Earth’s rotation makes an ‘aperture’ (the opening in an optical system that lets light through) from many smaller telescopes. ALMA has been used to view a massive forming star (AFGL 4176) which is 14,000 light years away with a luminosity 100,000 times brighter than the sun.
There are, however, even bigger telescopes or interferometers such as the VLA (Very Large Array) in New Mexico with a maximum baseline of 36km, e-MERLIN (Multi-Element Radio Linked Interferometer Network) in Britain with a maximum baseline of 217km and the VLBI (Very Long Baseline Interferometry) which is over the North American continent with a maximum baseline of 8611km! In addition, the EHT (Event Horizon Telescope) is one of the world’s largest Interferometers. To put into perspective, it has a maximum baseline of 10,700km! It combines many telescopes from all around the world to achieve a resolution of 0.000019 arcseconds which is the equivalent of being able to resolve a tennis ball on the moon. The highest resolution we’ve ever been able to achieve on Earth! It has been used to observe a supermassive black hole at the centre of M87 and the black hole at the centre of our Galaxy, the Milky Way. The significance of EHT was highlighted in the Sentinel Mission article saying: “This collaboration allows scientists to observe objects in space with unprecedented resolution and detail.” [1]
Therefore, to explore the universe and be able to see it in greater detail, we need these big telescopes and their greater resolution to do so.
[1] Tinelmis (2025) Event Horizon Telescope (EHT) - Definition & Detailed Explanation. Sentinel Mission.
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- The grammar and presentation of the blog is very good, you’ve got the title, date, and name of the speaker in there.
Overall: Excellent
- You’ve done a really great job of describing the take home message of the seminar!
Overall: Excellent
- You’ve got some context of the information that was given but it’d be nice to have a little more - what does better pictures allow astrophysicists to achieve?
Overall: Good
- You’ve got a good direct quote that emphasises the importance of the Event Horizon telescope.
Overall: Excellent
- The tone is very fun to read and most things are described to a level that a layperson would be able to understand. My one little thing is that you don’t define baselines, which makes the whole paragraph about interferometers a bit confusing for a layperson. It’d also be nice if you could specifically define interferometers as currently it reads as they are just big telescopes, instead of being a collection of them.
Overall: Good
Overall: A really fun and passionate read! Some small technical things if you want to be nit-picky but it’s really good! :)
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Great readability and and tone. Lay terms are helpful throughout, and use of external information. Got the gist of the whole seminar in a concise essay, nice job!