Episode 4, in which I show that spiral galaxies are very grubby – they contain huge amounts of dust. And not only galaxies – astronomical dust is everywhere we look. The Universe may be big, but it sure is dirty..
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Archive for the The Universe and Stuff Category
Watch “Why the Universe is quite disappointing, really – Episode 4” on YouTube
Posted in The Universe and Stuff, YouTube with tags astronomy, dust, galaxies, M31, M64 on May 19, 2020 by telescoperHubble Tension in Perspective
Posted in The Universe and Stuff with tags Cosmology, Durham, Hubble constant, Richard Ellis on May 18, 2020 by telescoperIn my office today for the first time in a couple of months I stumbled across a folder containing the notes from the summer school for new Astronomy PhD students I attended in Durham in 1985. Yes, that’s thirty five years ago..
Among the lectures was a set given by Richard Ellis on Observational Cosmology from which I’ve taken this little snippet about the Hubble Constant:
It’s not only a trip down memory lane but also up the cosmological distance ladder! You will see that there were two main estimates, one low and one high. Both turned out to be about three sigma away from the currently-favoured value of around 70.
Plus ça change, plus c’est la même chose…
Does this change your mind about today’s tension between another pair of “low” (67) and “high” (73) values?
Follow @telescoperThe Geostationary Orbit
Posted in Cute Problems, The Universe and Stuff with tags circular orbits, geostationary satellite, Gravity, satellite on May 16, 2020 by telescoperI’m was mucking out this blog’s blocked comments folder and unsurprisingly found a few from Mr Hine, a regular if sadly deranged correspondent.
One of his blocked comments begins
In the forlorn hope that Mr Hine might some day learn something scientifically correct I thought I’d repost this problem, which is very easy if you have a high school education in physics or applied mathematics but no doubt very difficult if you’re Mr Hine.
Verify that the radius of a circular geostationary orbit around the Earth is about 42,000 km, i.e. find the radius of a circular orbit around the Earth which has a period of 24 hours so that its orbital period matches the Earth’s rotation period, thus ensuring that an object travelling in such an orbit in the same direction as the Earth’s rotation is always above the same point on the Earth’s surface.
(You will need to look up the mass of the Earth.)
Follow @telescoperCosmology Talks: Adam Riess on Cepheid Crowding and the Hubble Tension
Posted in The Universe and Stuff with tags Adam Riess, arXiv:2005.02445, Cepheid varfiables, Cosmology, Hubble constant, Shaun Hotchkiss on May 15, 2020 by telescoperHere’s another example from the series of cosmology talks being curated by Shaun Hotchkiss. In this one, esteemed astronomer and Nobel Prize winner Adam Riess talks about what he and collaborators considered to be the leading candidate for a systematic error in the SHOES measurement of the expansion rate of the Universe. This is “Cepheid crowding”, the possibility that background sources change our interpretation of Cepheid brightness, ruining one step in the SHOES distance ladder. Riess and collaborators devise a nice way to test whether the crowding is correctly accounted for and find that it is, so crowding cannot be the “explanation” of an error in the distance ladder measurement of H0. Riess also stresses that both the early and late universe measurements of H0 are now backed up by multiple different measurements. Accordingly, if the resolution isn’t fundamental physics, then no single systematic can entirely solve the tension.
P. S. The paper that accompanies this talk can be found on the arXiv here.
Follow @telescoperHow to Solve Physics Problems
Posted in Cute Problems, Education, Maynooth, The Universe and Stuff, YouTube with tags education, How to Solve Physics Problems, Physics on May 14, 2020 by telescoperSince the examination period here at Maynooth University begins tomorrow I thought I would use the opportunity provided by my brand new YouTube channel to present a video version of a post I did a few years ago about how to solve Physics problems. These are intended for the type of problems students might encounter at high school or undergraduate level either in examinations or in homework. I’ve tried to keep the advice as general as possible though so hopefully students in other fields might find this useful too.
Follow @telescoperWatch “Why the Universe is quite disappointing, really – Episode 3” on YouTube
Posted in The Universe and Stuff, YouTube on May 12, 2020 by telescoperWhy the Universe is quite disappointing really – Episode 3, in which I give two examples of biological systems that are inefficient and poorly designed. If these are the product of intelligent design, the designer clearly wasn’t concentrating.
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Watch “Why the Universe is quite disappointing really – Episode 2” on YouTube
Posted in The Universe and Stuff, YouTube with tags Nuclear Physics, stars, Sun on May 8, 2020 by telescoperEpisode 2, in which I explain how stars limp along unimpressively, making very poor use of the resources available to them, not doing a very good job at what they’re supposed to be doing, and then they die.
Just like people really…
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Gruber Prize 2020: Volker Springel & Lars Hernquist
Posted in Open Access, The Universe and Stuff with tags Cosmology, Gruber Prize for Cosmology, Lars Hernquist, numerical simulations, open science, Volker Springel on May 8, 2020 by telescoper
I’m delighted to be able to pass on the news released yesterday that the 2020 Gruber Prize for Cosmology has been awarded to Lars Hernquist (left) and Volker Springel (right) for their work on numerical simulations.
The citation reads:
The Gruber Foundation is pleased to present the 2020 Cosmology Prize to Lars Hernquist and Volker Springel for their transformative work on structure formation in the universe, and development of numerical algorithms and community codes further used by many other researchers to significantly advance the field. The contributions of Hernquist and Springel have led to profound insights spanning billions of years of cosmic evolution, including simulations of the growth of early density fluctuations through to present-day galaxies, the influence of galaxy mergers on star formation, and the close coevolution of supermassive black holes with their host galaxies.
I’ll just add that as well as being enormously influential in purely scientific terms both these scientists have contributed to the culture of open science through making codes (such as GADGET) freely available to the community.
Heartiest congratulations to Volker Springel and Lars Hernquist on their very well deserved award.
Follow @telescoperWatch “Why the Universe is quite disappointing really – Episode 1” on YouTube
Posted in The Universe and Stuff, YouTube on May 6, 2020 by telescoperEpisode 1, in which I explain why stars are not very good at generating power and that a couch potato radiates more energy per kilogram than the Sun.
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In the Dark 