Astronomy 16: Modern Astrophysics

Prof. David Cohen

Fall 2014
Tu., Th. 9:55 to 11:10
SC 113 (seminar room)


Omega Cen Pleiades Arp 188 Eagle Nebula





posted 10/20

There is an SA session tonight, in SC 102, from 7:30 to 9:30. Note also that I have two separate sets of office hours tomorrow. The homework is due on Wednesday at 5pm.

posted 10/15

Please take some time over break to look at the sky - especially if you're spending the week someplace with darker skies than Swarthmore has. Also, I've posted some short, non-textbook reading, below, in the Assignments section. In a similar vein, play around with the orbit simulators I linked to last week, which I've left linked there too.

Planning for next week, please consider coming to the colloquium on Friday at 12:30 (pizza provided) in SC 199. It's by an alum, Ben Vigoda. Note that it's not (directly) on a physics research topic and might give you some insights into how physics knowledge, skills, and ways of thinking might lead to a job outside of academia.

A reading assignment for next week will be posted by Thursday. But if you're interested in preparing for next Tuesday's class now, you could review some nuclear reactions (p-p chain vs. CNO cycle and also triple-alpha) and reread the end of Ch. 15 (sec. 4). Update 10/15: it's now posted.

We will have a lab meeting on Wednesday night (Oct. 22). Information about the lab will be posted by the weekend. But the M17 reading and the associated information posted below are good preparation for the lab.

And a new homework assignment will also be posted soon. Update 10/16: it's now posted.

Archive of old announcements.


posted 10/14

Our fourth homework assignment is quite short. It's due on Wednesday, October 22.

posted 10/15

Take a look at the reading assignment for next week's classes.

We'll be doing some more data reduction and image manipulation on Wednesday in lab. You can start thinking about what object you'd like to observe. Take a look at this short article with many pictures about M17, a giant star formation region. The "M" designation means the object is in the Messier Catalog of fuzzy objects that might be mistaken for a comet by an 18th Century astronomer. There are links to articles about other Messier objects at the bottom of the article.

Note that you can start to see some of the concepts we've been discussing in a more abstract, physics context in class come into play in the article. Massive stars with short lifetimes because of their very high luminosities, for example. And note also that at the end of the article a multiwavelength view of M17 is given. There is a strong X-ray source in the nebula, which the author says could be an accreting black hole or a background quasar. But I'm actually working on a paper now showing that it's a quadruple system of four massive stars (two pairs of binaries that are themselves orbiting each other) and that the strong X-ray emission comes from interactions between the powerful winds of each binary pair.

Also: The images in the article are beautiful! Ours won't be as good. And we can't observe this object anyway, as it's setting soon after sunset. If you want to see how observable a given object might be, you can use the Tapir software written by Eric Jensen - try the airmass plots (the airmass is the cosecant of an object's altitude). And also try making a finding chart. Take a look at some of the Messier objects and think about which one you'd like to observe.

Finally, the Stellarium software the author uses to make plots of the sky is freely available (see the link on the right side of this page).

While reading a few of the Messier posts, I came across this post debunking a "cold fusion" device. It's quite brief, but touches on much of the same physics as our discussion of nuclear reactions last Thursday. It even has the plot of nuclear binding energy vs. atomic mass that I drew on the blackboard. Take a look.

posted 10/9

Play around with this gravity simulator. Note how if you set up any array of masses, they'll all collapse into a single large mass. To get orbits, you need to give some objects (tangential) velocity.

Planet Crash is another simulator/game. You have to start with circular orbits, but it has other interesting features.

Archive of old assignments.

Upcoming Events

Check the departmental colloquium schedule. You should come to these talks. They are typically Friday at 12:30 in Rm. 199, and include pizza.

There are telescope public viewings the second Tuesday of each month, at the Peter van de Kamp Observatory on the roof of the Science Center. The next one is on November 11, at 8 PM. Astro 16 students are welcome to come and help out. It is also an excellent opportunity to show your friends the observatory and the view of astronomical objects through our telescope.


Class Information

Read the class announcement [pdf]

A syllabus [pdf] (Updated 10/14) is available
note that it will be periodically updated

office hours for week 7


Astronomy Picture of the Day

Messier 42; with links to articles about each Messier object

Physical constants and astronomical constants from the appendix of our textbook

what's up in the sky this week

Stellarium software for making sky maps

using your hands to measure angles

sky and weather information

observatory website

department website



This page is maintained by David Cohen
cohen -at-

Last modified: October 20, 2014