Archive for September, 2019

The Problem of the Disintegrating Asteroid

Posted in Cute Problems, The Universe and Stuff with tags , , on September 30, 2019 by telescoper

I thought you might enjoy this entry in the Cute Problems folder.

An asteroid is moving on a circular orbit around the Sun with an orbital radius of 3AU when it spontaneously splits into two fragments, which initially move apart along the direction of the original orbit. One fragment has a speed which is a fraction 0.65 of the original speed, the other has a speed of 1.35 times the original speed. The original orbit (solid line) is shown above, along with the two new orbits (dashed and dotted).

  1. Which orbit does the fast fragment follow, and which the slow fragment?
  2.  Calculate the original orbital speed in AU/year.
  3. Calculate the angular momentum per unit mass, h, of the original asteroid and of each of the two fragments in units of AU2 per year. [HINT: Show that in these units, for a general orbit of eccentricity e and semi-major axis a, h2=4π2 a (1-e2).]
  4.  Calculate the eccentricities of the orbits of the two fragments.
  5.  Calculate the orbital periods of the two fragments in years.

Answers please through the Comments box. First complete set of answers wins a trip to the Moon on gossamer wings.



More on Comments

Posted in Uncategorized with tags , , on September 29, 2019 by telescoper

At the end of the month I usually give the blog a bit of a clean out, especially the blocked comments that have accumulated in my filter. Here’s just a sample of the contributions from my admirer, Mr Hine. These are just a few of the dozens of comments he’s failed to post here. No doubt he’ll try to post some more gibberish when he sees this but although I know it makes me a bad person, I just can’t resist winding him up.

A Drunk and Disorderly Brexit

Posted in Politics with tags , , on September 28, 2019 by telescoper

Having to return to Parliament following the Supreme Court’s unanimous (and undoubtedly correct) decision that Boris Johnson’s attempted prorogation was unlawful seems to have driven certain Tories to drink (or something stronger).

The clip above shows a clearly inebriated Michael Gove (not just an MP but a Cabinet Minister) in the House of Commons.

More generally I’m sure that alcohol played a big part in the appallingly offensive language and shouty behaviour coming from the Government benches, including from the Prime Minister who, for some reason, has not yet resigned but is regularly too tired and emotional to speak any sense at all. It wouldn’t surprise me if he were to be found dead drunk in a ditch before too long.

The Houses of Parliament are supposed to be places of work for MPs. Most of us would be summarily dismissed if we turned up at our workplace steaming drunk and I don’t see any reason why it should be any different for Members of Parliament.

If I had my way all MPs would be breathalysed before being allowed to participate in a debate or vote at a division. Anyone over the limit should be barred.

After much sobre reflection, I think keeping the drunk and disorderly out of Parliament might not only improve the quality and civility of the debates but also improve the decision-making of the House.

What do you think?

Research Evaluation

Posted in Uncategorized on September 27, 2019 by telescoper

I get quite a few of these spam invitations to fake academic conferences, but I have never had one before with such an obviously back-handed compliment about the quality of my research!

End of Summer Rains

Posted in Cricket, Maynooth with tags , , , on September 26, 2019 by telescoper

The rain is pouring down here in Maynooth, but this isn’t the only place to have had inclement weather today:

The picture above shows the scene this morning at Chester-le-Street in County Durham where the County Championship Division 2 match between Durham and Glamorgan was taking place. Or rather, wasn’t taking place. The game was abandoned this morning owing to a the cumulative effect of heavy rain over the last few days that allowed only 86 overs to be bowled in total over the four days.

This match being declared a draw, Glamorgan finish the season in 4th place on 167 points, missing out on promotion to Division 1 but having performed much better than last season. They were top of the table early on, but the loss of the excellent Marnus Labuschagne to Ashes duty for Australia proved a big blow and they fell back in the second half of the season. Anyway, at least they’ll probably win a few games next season, while they would undoubtedly struggle in Division 1. Lancashire finish top of the Division 2 table by a country mile, while Northants and Gloucester also go up.

I always thing of the last day of the County Championship as the end of summer. This year most of the final round of games has been hit by the weather so it’s a rather damp ending. This is also the first year in a while in which I haven’t seen any live cricket. Still, there’s always next year.

That’s basically all I have time to write about today as I’ve been running around all day – including popping into the library to give the webinar I mentioned yesterday. Moreover, at 6pm local time all the power in the building is going off and we’re to be turfed out while some repair work is done. I’ll shortly have to go round checking all the computers are switched off.

The Open Journal of Astrophysics: Scholastica Webinar Reminder!

Posted in Open Access with tags , on September 25, 2019 by telescoper

Just a quick reminder that tomorrow I’ll be participating in webinar (whatever that is) organized by Scholastica to do a about the Open Journal of Astrophysics, which will involved a short presentation delivered over the interwebs jointly by myself and Fiona Morley (Head of Digital Programmes and Information Systems at Maynooth University Library), followed by a question and answer session. The session will be conducted via Zoom (which is the pretty neat platform we use, e.g., for Euclid teleconference meetings).

Here is the advert:

You can sign up here.

Now I have to figure out what I should say.

Johnson Close To Deal

Posted in Politics with tags , on September 25, 2019 by telescoper

Thank you, Google, but that isn’t really the information I was looking for.

Supreme Predictions

Posted in Politics with tags , , , on September 24, 2019 by telescoper

This morning the Supreme Court delivered a ruling that the UK Government acted unlawfully in its recent prorogation of Parliament and so Parliament is consequently no long prorogued. After its decision in this case that the Prime Minister prorogued Parliament with the intent of stopping it carrying out its duties, I look forward to a similarly shocking ruling in the vexed matter of whether or not ursine mammals defecate in forested areas.

I have noticed over the years that everyone on Twitter is – or at least thinks they are – a legal expert, so not to be outdone I last night posted my own prediction of the Supreme Court ruling:

My legal acumen having been established beyond any reasonable doubt, I mention for the record that I posted this tweet at the same time:

This is the correct way to make predictions in the age of social media.

Diana Ross is 75.



New Publication at the Open Journal of Astrophysics!

Posted in Open Access, The Universe and Stuff with tags , , , , , , , , on September 24, 2019 by telescoper

Yesterday we published another new paper at The Open Journal of Astrophysics, but I didn’t get time to write a post about because of teaching and other start-of-term business so I’m correcting that omission now.


The authors are Selim Can Hotinli  of Imperial College London (UK), Marc Kamionkowski of Johns Hopkins University, Baltimore (USA) and Andrew Jaffe, also of Imperial College.

You can find the accepted version on the arXiv here. This version was accepted after modifications requested by the referee and editor. Because this is an overlay journal the authors have to submit the accepted version to the arXiv (which we then check against the copy submitted to us) before publishing; version 2 on the arXiv is the accepted version.

You will see that this is  one for the `Cosmology and Nongalactic Astrophysics’ folder. We would be happy to get more submissions from other areas, especially Stellar and Planetary astrophysics. Hint! Hint!

P.S. Just a reminder that we now have an Open Journal of Astrophysics Facebook page where you can follow updates from the Journal should you wish..

The Autumnal Equinox 2019

Posted in Maynooth with tags , , on September 23, 2019 by telescoper

The Autumnal Equinox (in the Northern hemisphere) took place today (Monday 23rd September 2019) at 8.50am in Ireland.

People sometimes ask me how one can define the `equinox’ so precisely when surely it just refers to a day on which day and night are of equal length, implying that it’s a day not a specific time? The answer is that the equinox is defined by a specific event, the event in question being when the plane defined by Earth’s equator passes through the centre of the Sun’s disk (or, if you prefer, when the centre of the Sun passes through the plane defined by Earth’s equator). Day and night are not necessarily exactly equal on the equinox, but they’re the closest they get. From now on days in the Northern hemisphere will be shorter than nights and they’ll get shorter until the Winter Solstice.

For many people the autumnal equinox is taken to be the end of summer, though there is a saying around these parts that `Summer is Summer to Michaelmas Day’ (which does not happen until September 29th). Nevertheless it is the first day of teaching term and the start of the last round of this years matches in English cricket’s County Championship. The end of the cricket season is the end of summer as far as I’m concerned, though I haven’t seen any matches in person this year.

Over the past week or two the new students have been going through various induction and orientation processes, but their first encounter with actual teaching will be tomorrow. I will be greeting our 94 new first-year Mathematical Physics students at 11am on their first day. I hope I don’t put too many off.  Then I start the fourth-years off on  Astrology and Cosmetics Astrophysics and Cosmology. That is assuming that I take the right notes to the right lectures.

Anyway, I think that’s enough rambling for now. I’ve got to finish getting my notes together for the next few days. Let me end by wishing the new and returning students at Maynooth  all the best for the new academic year. That goes for all students everywhere too! Work hard, and enjoy your studies, but don’t forget to enjoy life on the way!