How do we know what the Milky Way actually looks like, when we're inside it? I asked Mark Reid, Senior Radio Astronomer at the Harvard-Smithsonian Center for Astrophysics.

For more with Mark Reid on the Milky Way, check out the Q&A below.

NOVA: Do we know what the Milky Way looks like?

Reid: The answer really is no. At this point, we do know it is a spiral galaxy, we know it has spiral patterns, but we don't really know where these spiral arms lie. There's even debate between astronomers about whether there are two or four arms. I would say within the next few years when we've been able to map the positions of young stars that trace out these arms, then we'll know exactly where the arms are, and how many there are. We have good preliminary evidence to show there are four arms. And we know a little bit more about how tightly bound or open the arms are, there's been some debate about that, and it looks like it's a fairly loosely bound spiral, but to go beyond that it'll take a lot more observations and data.

NOVA: What are some of the challenges to studying the Milky Way?

Reid: The dust and gas in the Milky Way really makes it difficult for astronomers who use optical telescopes to see very far at all. And so the idea of measuring the distance to very distant stars with optical telescopes and making a map out of all that data won't work very well. You just can't see far enough. So you really have to use other techniques. You could use infrared light, or you could use radio light. What I use is radio light.

NOVA: Radio light?

Reid: Radio waves are light, they're not sound. They can be used to carry sound if you want, as people do with radio stations, but radio waves are still light. Your eyes just can't see. Radio telescopes collect radio light in much the same way that optical telescopes collect optical light. The ones I'm using are called the Very Long Baseline Array; there are 10 of them, all across the US from New Hampshire to Hawaii to the Virgin Islands, and a lot of them in between. By a technique called very long baseline interferometry, I'm able to make an image of what the sky would look like if your eyes could see radio waves, and if they were as big as the earth.

NOVA: Why use radio light?

Reid: The one advantage we have with radio light--with all these telescopes all across the earth--is it gives us incredible resolving power. We can measure very, very small shifts in angle as the earth goes around the sun, and from that we can calculate the distance to the star. That's a very powerful technique which you can't really do with any other wavelength at the moment. It's directly analogous to a surveyor measuring out a plot of land. A surveyor will look at object against a background, and will move to a different angle and measure again. If you know the baseline and angles you can calculate the distance. We've just extended that technique by a factor of a billion or more.

We can not only measure where things are, we measure how fast they're moving. So for every star forming region in the Milky Way, we look at how they're moving, so we know how the Milky Way rotates. From our observations we can tell how fast the milky way spins, and it tells us how much mass in the Milky Way--we figured out 15% faster than thought, and the mass of the galaxy is 50% more than before.

NOVA: What do you look for?

Reid: We look at very young stars. You can't detect stars with radio waves, but you can detect the clouds of gas around them because they just formed. Most of the gas is hydrogen, but there are trace amounts of water. The water molecules can act like a MASER, which is a radio wavelength version of laser light, which lets use measure position very well. Now there are probably only 500-1,000 of these very bright very young stars that have formed in the Milky Way at any one time, but the nice thing is they're very bright and trace out the spiral arms very nicely, much like in other galaxies.

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How to Pull an All-Nighter

It's final exam season again, and for students across the country, the midnight oil is burning bright. Yet a question looms: It's the morning after an intense all-night cram session, and there's a little bit of time before that big test. Should you take a short nap? Or is it better to just stay up? I decided to ask Dr. Christopher Landrigan, Director of the Sleep and Patient Safety Program at Brigham and Women's Hospital.

For more with Dr. Landrigan on the science of sleep and sleep deprivation, check out the Q&A below.

NOVA: How did you get interested in studying sleep deprivation?

Landrigan: My interest in patient safety and sleep deprivation began in my own training as a resident at Children's Hospital. Fifteen years ago, there were no limits on how much doctors in training could work, and I often found myself at the tail end of a 36 hour shift, not performing my best. I got interested in this later. Was there an impact this might have on the safety of our patients?

NOVA: Why do we feel sleepy?

Landrigan: There are a number of different factors that drive human alertness and performance. The first is something called the sleep homeostat. It's a seesaw system: The longer you've been asleep, the greater the drive to wake up, and the longer you've been awake, the greater the drive to sleep. There's also the circadian system, a 24 hour biological clock that tends to drive maximum performance in the daytime, and drives maximum sleepiness in the early hours of the morning. If we stay up past the point where our bodies are telling us to go to sleep, then the sleep homeostat system and the circadian system both start working together to force you to go to sleep.

NOVA: What happens when you don't sleep?

Landrigan: We know that reaction time goes down, that your ability to put together complex puzzles in your mind, even to do simple math seems to deteriorate. It's not exactly understood how sleepiness contributes to degradation of cognitive function, but we know from imaging studies that the ability of the brain to metabolize glucose, to do what it's supposed to do, tends to decrease after you've been up too many hours in a row.

There have been a number of studies that have tried to look at the effects of sleep deprivation on performance and compare those to the effect that's induced by alcohol. It's been consistently shown that wakefulness of about 17-20 consecutive hours leads to performance decrements that are more or less equivalent to those induced by a BAC [blood alcohol content] of 0.05. And at the 24 hour mark, on average we will perform as if we had a BAC of 0.1, which is beyond the legal limit. With sleep inertia, sometimes the sleep decrements can be even greater than that 24 hour level.

NOVA: What's sleep inertia?

Landrigan: It's a slowness in the brain, an inability to react as quickly or to perform cognitive functions as well in the first few minutes after awakening. Sleep inertia is really the idea that the brain doesn't go from zero to 60 in six seconds. In fact it can take many minutes to even a couple hours for it to wear off.

If somebody is sleep deprived on a regular basis, there's a tendency to go into a deeper stage of sleep more quickly, and when woken from deeper stages of sleep, it appears that sleep inertia is most profound. So if you are sleep deprived and you're rapidly woken from sleep for whatever reason, the tendency to have sleep inertia where performance is really impaired for a long period of time is at its worst.

NOVA: What's so bad about not getting enough sleep?

Landrigan: We're only beginning to understand what the adverse consequences of this may be. From long term studies, it's pretty clear that not only do performance failures increase after sleep depriving ourselves, but there's a really a very substantially increased risk of safety problems--for drivers, for people in high risk occupations in risky industries, as well as long term health consequences of this sort of thing. We know that people who deprive themselves of sleep or work shift work on a regular basis are at higher risk of diabetes, metabolic syndrome, heart disease, hypertension, obesity, and so on for years to come.

To the extent that one can, thinking a little bit constructively about schedules and planning a little bit ahead to minimize all nights and minimize sleep deprivation. It's going to do you a world of good down the road.

Kevin Jiang

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