LRO image of the Apollo 17 landing site. Courtesy NASA Goddard Space Flight Center.
You know how some people refuse to acknowledge that humans never went to the Moon? That kind of head-in-the-Earth-sand thinking is somewhat sad and delusional, since the evidence lies before us in images taken of the Moon’s surface by the Lunar Reconnaissance Orbiter. Those views show the sites of the Apollo 12, 14, and 17 landings in sharp detail. We see tracks across the dusty lunar surface left as people actually walked from the landers to various parts of the landing sites. NASA released a set of images taken with the LRO’s Narrow Angle Camera that show tracks and trails, as well as landers. What really impresses me is that the sharpness of the paths hasn’t changed much over the years since they were made. The simple explanation? The Moon has no atmosphere, no wind, no rain, nothing to erode the paths. And so they remain, as evidence that people once walked these regolith-rich areas and explored another world. When will we get to do it again?
Hurricane Irene over the Bahamas, August 24, 2011. Shown by the Moderate Resolution Imaging Spectroradiometer on NASA's Aqua satellite. Our ship was about 350-400 miles north of this storm, just outside the outermost cloud bands. Courtesy NASA.
Nature is a great thing to contemplate when you’re floating on the ocean in the wake of a hurricane. That’s where I was last week, in my role as an astronomy speaker on board a cruise ship. I do these trips several times a year, and usually the worst weather we get is a squall that rocks and rolls the ship for a few hours. If I’m lucky, it happens when I’m NOT “on duty”, but occasionally I have been known to rock and roll across the stage while sharing the latest and greatest astronomy news with my fellow shipboard travelers. In the case of this last cruise, long swells rocked the ship, and so I spent one of my talks hanging onto the podium up on the show stage. Everybody else got to sit safely in the comfort of the show lounge seats as I took them on a tour of the cosmos.
One of the fun parts of doing these trips is answering questions from people about astronomy. Often those questions come at the end of my presentations, but they also pop up at dinner, or when I’m on a walk around the deck.
A supernova discovered in the galaxy M101 (the Pinwheel Galaxy), courtesy of University of California-Santa Barbara.
While I was on board, astronomers announced the discovery of a supernova in the galaxy M101, which lies about 21 million light-years away from Earth. I had a quick look at the early images and noticed that the galaxy’s shape had a kind of a neat similarity to the shape of the hurricane we were avoiding. It had nothing to do with the supernova, of course, but I often notice these things because I’m just a visual type of person, I guess.
Of course, the supernova didn’t make the news we were seeing aboard the ship, since the hurricane was rocking the ratings on all the news channels we could get. But, I did have a few people ask me about the supernova as I sat down in the Internet Cafe to check mail one day. Such questions are one reason I always spring for the Internet package aboard the ship—to check for news so that I’m not totally surprised by a fellow passenger who happens to read of an astronomy discovery before I do.
Anyway, one person asked me what the big news was about the supernova, since I had mentioned in one of my talks that supernovae have been observed not just in our own galaxy, but in others. After all, she wanted to know, don’t stars blow up all the time? I liked that she’d kept the idea of star death fresh in her mind.
This particular stellar death event was what astronomers call a Type 1a supernova. It flared up very quickly, and was as bright as a billion Suns right after its explosion began. One of the astronomers who is working on observations of this supernova, called the stars that are involved in flareups like this one “zombie stars.” They’re dead stars (called white dwarfs), but their cores contain the ashes of materials they’ve “burned through” earlier in their lives. They have a gravitational pull on material from a companion star, and as they suck that material in, they come back to life and flare up in brightness, as astronomers (both professional and amateur) watched the star in M101 do. Over the past 50 years, astrophysicists have discovered that Type Ia supernovae are part of binary systems, which are made up of two stars orbiting a common center of gravity. The one experiencing the explosive activity is the white dwarf star.
There are other types of supernovae—the Type II variety—that result from the deaths of massive stars that collapse rapidly and then explode outward. We talked a lot about those on the ship, mostly because their remnants look very cool. Think of the Crab Nebula, for example. It’s the result of a hugely massive star essentially imploding on itself and then bursting outward, flinging its material to space. Those kinds of images really captivate people. The Type 1a explosion took a little more explanation, but when we got through talking about it, my fellow passengers walked away with a bit of wonderment in their eyes—and satisfaction at being able to understand a little bit about the really neat things that astronomers get to study in the ocean of space.
To a large extent, that’s why I talk about astronomy to public audiences when I can, not just on cruise ships, but through this blog and my videos and other work. It’s just plain fun to explore the ocean of space and seek to answer those big (and little) questions that pique our curiosity about the cosmos.
