Podcast: Light Pollution

Special Correspondent Julie Wilbert brings us a podcast report on light pollution with members of the Minnesota Astronomical Society.

Light Pollution (MP3, 17.2MB, 18:40)

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Astronomy Blog reminds us: Don’t name a star

Stuart over at Astronomy Blog tackles and tackles again the reasons why you should not pay to “name a star” for yourself or a loved one. While it can be heartfelt to want to memorialize someone by naming a star, you can do that without sending a check to shady unofficial organizations.

Hell, just email us and we’ll help you pick out a great star. You want something hot? Massive? With or without a companion? Would you like an accretion disk with that? Or some planets perhaps?

Go ahead, name a star. Just don’t pay for it.

Amateur Astronomers from KQED

Here is a nice video from the KQED QUEST Science Video Podcast called Amateur Astronomers. It features John Dobson, Timothy Ferris and many others. Looks like a pretty cool podcast in general.

Whatever the hell is Slacker Astronomy?

I posted this to the feed a while ago. It’s a short-ish podcast which discusses the history of Slacker Astronomy with Aaron Price, the founder of Slacker Astronomy, and includes random musings by yours truly about the future of the podcast/blog. I marked this explicit in iTunes because I use the f-word once.

Whatever the hell is Slacker Astronomy (MP3, 17MB, 18:30)

As always, we welcome your feedback so email us if anything comes to mind.

Doug shows us the light

Our own Doug Welch wrote a very nice article in the latest issue of Sky and Telescope called “How to Hunt for Supernova Fossils in the Milky Way“. I can’t find a link to the article itself but S&T has a post about the article.

It’s really cool stuff — an accidental discovery of supernova light echos in the LMC has led to a new way to look for and study supernovae here in our own galaxy.

Doug discusses in detail how you can help hunt for these elusive light echoes. It would be a great multi-year project for a small college astronomy program or for accomplished astrophotographers with a bunch of really nice equipment.

Doug also describes in the article what happens if you find a light echo:

What happens if you find a candidate light echo? You become my new best friend!

How can you pass that up?!?

Differential Equations

I’m taking a class on Differential Equations. These are hard to explain but I’m going to give it a try. To do so I am going to try to explain differential calculus in a nutshell.

Your driving down the road in an automobile. You have an odometer in the car which tells you how far you’ve gone (x). You have a speedometer which tells you how fast you are going (v). When you punch the gas pedal or hit the brakes, your car accelerates (a), getting faster or slower. All of these quantities are related through calculus. Let’s say you start at x=0 and drive at v=40 miles per hour for t=15 minutes.

x = vt
x = (40mph*0.25 hours)=10 miles

We can write this as x/t = v. The velocity is the ratio of the change in position (x) to the change in time (t).

In math instead of saying “change in x” we say “delta-x” . In calculus we take this delta to be infinitely small and instead of saying “delta-x” we say “dee-x” (and write dx). So when I write dx I just mean a ridiculously small change in position. dt means an instantaneously small slice of time. The equation v=x/t can be written with this notation as v=dx/dt. This means the same thing as above, it’s the same definition of velocity, but we are implying these infinitely small deltas.

Another way of saying dx/dt is to say “the time derivative of x”. This just means “how x changes with time”. If we assume that we are talking about time we can use a shorthand which means “how x changes with time” and that shorthand is simply a single apostrophe like this: x’.

Now we can write our equation above like this:

v = x’

But your velocity can change over time, too. If you are going 40 mph and accelerate to 60 mph, your velocity changes as a function of time.

v = at

For some length of time (t) you accelerated at a rate (a) and your new velocity is your original velocity plus (a) times (t). If we rewrite:

a = v/t

and using our notion of infinitely small deltas:

a = dv/dt

we find that (a) has the same relationship to (v) that (v) had to (x) and thus

a = v’ = x”

So we have:

x The position
x’ The velocity
x” The acceleration

The velocity is referred to as the “first derivative of x” and the acceleration is referred to as the “second derivative of x”. These derivatives have a mathematical relationship that is beyond the scope of this article.

Now to differential equations. These are equations where we see complicated relationships between values and their derivatives. An example is a falling object (m) reaching terminal velocity due to wind resistance. The force on this object (F=ma) is the difference between the gravity (g) of Earth pulling it down (-mg) and the wind resistance (k) getting stronger as the object falls faster (kv):

ma = kv - mg

For simlicity we divide by m and just let k = k/m:

a = kv - g

and now use our fancy notation from above:

x” = kx’ - g

or equivalently:

v’ = kv - g

In this equation the change in velocity is a function of the velocity itself. So to know the acceleration you need to know the velocity but to know the velocity you need to know the acceleration!

This is the conundrum of differential equations. Finding functions that, when you find their derivative, give themselves back.

If you solve the equation v’ = kv - g the answer you get is the velocity as a function of time. If you plug in a very long time, the velocity reaches a limiting value — the terminal velocity.

You can’t really solve this problem without differential equations. It turns out there are many, many things in the real world, in physics, biology and engineering, that can be explained with differential equations. From orbits to population growth to thermodynamics, differential equations are actually quite useful.

Congratulations if you stuck with me! If you guys are interested we can talk a little about differential equations in astronomy next time.

Please comment

We’ve had a report that our comments weren’t working on this blog. I tested it and it worked OK for me. Can you please try to comment and/or email us at info@slackerastronomy.org if you have problems?

Thank you!

We have a new show in the works.

Michael

Not in Cambridge

It pains me deep in my heart that I am not on my way to the joint AAVSO/BAA meeting in Cambridge, England. I believe our good friends Doug and Pamela are both there. I have been a loyal AAVSO member for quite a few years now and I have been to many of the meetings in exciting places like Rockford, Ill. and Las Cruces, NM. But can I make it to the one in Cambridge-freaking-England? No, apparently I can’t. Something about having a sick 4-month old baby, an energetic 4-year old, a thriving business, a very hard math class and 19 other areas in which I dabble, I am bankrupt of time. I planned on going, leaving tonight and coming home Sunday, but it didn’t make sense to try to cram an exhausting trip in just a few short days.

So, cheers, my brethren. Please toast my absence with proper British ale. For you dear readers on the right side of the pond, think about heading up to Cambridge tomorrow!

M.

Podcast interview with Brant Robertson

We have a new show! Doug and I had a great chat with Brant Robertson, who is a Spitzer Fellow doing research at The Kavli Institute for Cosmological Physics. Brant is a theoretical astrophysicist involved with computer simulations of the evolution of galaxies.

Check this sh!t out:

Credit: Brant Robertson, Spitzer Fellow, KICP/UChicago

This interview is quite long so we’ve uploaded low and high rez versions. The low rez version is the one in the RSS feeds.

If you subscribe to the feed, the audio is probably already on your box. Or you can check out the show notes or download the MP3 file directly:

Slacker Astronomy podcast interview with Brant Robertson (low rez) (MP3, 24.7MB, 1:11:20)

Slacker Astronomy podcast interview with Brant Robertson (high rez) (MP3, 65.6MB, 1:11:20)

Enceladus has gas

Phil “The Bad Astronomer” Plait has a nice article on new results from Cassini.

Coupled together, these two items indicate that if there is an ocean beneath the frozen crust of the moon, then it’s reasonably warm, and rich in organic compounds. We don’t know how life started on Earth, but it’s a good guess that an ocean thick with organic compounds was involved at some point.

We don’t know how common life is and the possibility that life exists on Enceladus is quite small. Still, research in the solar system and in the deep oceans of Earth are suggesting some exciting new possibilities for environments suitable for life.