A friend: “Hey, did you see that blue moon last night?”
Me: “Uh, yeah, I went outside and took a peek.” (Even if I didn’t.)
Look, don’t misunderstand. I’m all for anything that gets people outside and looking at the sky, and if overblown media stories about “super” moons and “blue” moons accomplish that, then it’s a good thing. But let me explain why I don’t get all that excited about it.
- Full moons are right up there with clouds as enemies of astronomical observing. Not only are they so bright that they wash out anything but the brightest stars and planets, they really aren’t much good for lunar observing, either. With the sun directly over the middle of the lunar disk, there are no shadows, and therefore no relief. Compare these two images of the lunar crater Hipparchus, which is near the center of the moon as we view it from Earth. This first one is taken when the moon is nearly full, almost completely illuminated.
Now look at this image taken near first quarter, when we see the lunar disk as half-illuminated, with the sun casting long shadows over Hipparchus (which is the central crater). I’ve rotated this image to give it roughly the same orientation as the first one. Look at how much more detail is visible. Can you even tell you are looking at the same object?
Read more ›
On a crisp Bedford County day in early 2007, I walked slowly around a ridge in the middle of a cleared field at Lynchburg College’s Claytor Nature Study Center. The ridge was the highest point on the property, but I wanted to be sure the view was such that tree lines in all directions were as low as I could get them. Walking in small circles, finally I stopped and said (apologies to Brigham Young), “This is the place.” The pier for the Margaret Gilbert telescope at the Belk Observatory now stands under a dome at that spot.
What makes a good spot for an observatory? First of course, you need to own the land or at least have permission to build on it. When Lynchburg College was gifted with the Claytor property in 1998, it provided both the land and the dark skies that an observatory needs. LC’s gorgeous campus doesn’t really have the space—even I wouldn’t dream of putting an observatory in the Dell—and the lighting on and around our campus means much of the sky would simply be washed out. So two factors are obvious and were met by our Bedford county site: relatively unobstructed views and relatively dark skies. What other factors are important, and what makes for an “ideal” location for an observatory?
- Clear skies: There is a reason that there are no world-class observatories east of the Mississippi River. Our cloudy and rainy summer of 2013 has been especially frustrating as we seek to calibrate our telescope and open the facility to the public. The more clear nights, the better your chances of seeing the sky. You can see from the image below why there are major observatories in Southern California and Arizona, and not in Cleveland, Buffalo, or Portland!
Read more ›
Last July, I posted about the possibility that the Curiosity spacecraft might be captured during its parachute descent to the Martian surface by another spacecraft in Mars orbit, the Mars Reconnaissance Orbiter. Indeed it was, and the resulting image is below. Astounding! One human-made robot in orbit around Mars images another human-made robot on its way to the surface. We truly do live in an age of wonders.
Wait a minute! Isn’t plutonium that nasty stuff they make bombs from? Radioactive? The stuff Doc Brown stole from Libyans to fuel the Back to the Future DeLorean time machine? Well, yes…but there’s more to it than that.
Plutonium exists as several different isotopes, forms of a single element that differ only in the number of neutrons in their atomic nuclei. Their mass number is the total number of protons and neutrons. The isotope of plutonium that is used in nuclear weapons is plutonium-239, but the isotope we want to talk about is plutonium-238 (Pu-238).
Pu-238 is used as a power source—not for time machines, but for spacecraft. Two of its characteristics make it especially suitable for that purpose.
- Almost all of the radiation emitted by Pu-238 is of a type that is easily stopped by minimal shielding. That translates to less weight needed to shield the rest of the spacecraft from this radiation.
- It has an almost ideal half-life of 88 years. This is both long enough and short enough: long enough to last for decades on a long space mission, and short enough to provide lots of energy from a relatively small amount of material. Think for a minute about how the half-life of a radioactive material affects its activity. If half of it decays (emitting energy as it does so) in 100 years, that is a lot more energy than if the same amount of material takes a million years to decay. Shorter half-lives translate into higher activities.
Read more ›
In the post just previous to this one, you saw some views of Earth and Saturn generated by a very useful online tool, Solar System Simulator. I thought I would use that tool to show you the Cassini spacecraft’s changing view of Saturn as it moves from its current position today (July 10, 2013) to the point at which it will aim its camera toward Earth on July 19. We’ll use the same time (5:30 p.m. EDT) each day to separate each image by 24 hours. Keep in mind that in the last image, even though the Sun is not obscured by Saturn, the camera will be pointed at Earth, not the Sun. The camera will sweep from right to left for over four hours, and by the time it gets to the left edge of Saturn, the Sun will be behind the planet. Enjoy flying with Cassini!
One of the most astounding images of the space age is about to be replicated. Take a look at this image of a backlit Saturn eclipsing the sun. This is a mosaic of images taken over three hours in September, 2006, adjusted to resemble natural color as closely as possible, taken by the Cassini spacecraft currently in orbit around Saturn.
But this picture has been resized to fit on a typical computer screen. Here is the link for a full-resolution image. The night side of Saturn is illuminated by reflected light from the rings. The rings are backlit; the sunlight is being scattered through the ring particles. Outside the bright main rings that circle nearer the planet, you can see the diffuse, dim and narrowly confined G ring. The broader E ring encircles the whole system. The small moon Enceladus, whose icy eruptions are the source of the particles in the E ring, can be seen embedded in the ring at its far left edge. And over 700 million miles away, on the left between the G ring and the brighter main rings from this perspective, is a pale blue dot that is our home planet Earth.
An image such as this could only exist in our imagination before the era of interplanetary space missions—and it’s about to happen again.
Read more ›
“What’s the coolest thing you’ve ever seen through a telescope?”
People who know—or who learn—that I taught astronomy and was the director of an observatory with a half-meter telescope often ask questions like this. Variations on the theme include “What’s the most distant object you can see?” or “Can you see Pluto?” (Respective answers are: probably 3C 273, an unusually bright quasar that is 2.4 billion light years distant; yes, but it’s not much to see.) I’ve developed some stock answers over the years and can trot them out semi-automatically. But this was an old high school and college friend I had not seen for more than thirty years, and he deserved a more thoughtful answer. And since all of these objects are currently in the night sky, they came easily to mind.
Without a doubt, Saturn is my favorite planet of all, especially when its gorgeous rings are tilted so that they are more prominent. A 20-inch telescope and good seeing conditions will show the famous Cassini division, the shadow of the rings on the planet, and the shadow of the planet on the rings.
Read more ›
Radioactively hot, that is.
While the Curiosity Mars Rover was cruising for eight months between Earth and Mars, one of the instruments aboard was measuring the radiation levels encountered along the way. The Radiation Assessment Detector—RAD—was inside the spacecraft, shielded in much the same way as astronauts would be on an interplanetary mission. Now the same instrument is continuing to monitor those radiation levels on the Martian surface. The results from the interplanetary cruise phase of the mission were recently released, and while they don’t rule out interplanetary voyages by humans, they do highlight a significant risk.
Let’s do a Q & A to address some background material and some of the issues involved in order to better understand this.
Read more ›
The two brightest planets in the sky, Venus and Jupiter, have been drawing closer and closer to each other as seen from Earth for the past several days. This weekend they will be joined by the hard-to-see innermost planet Mercury for a rare triple planetary conjunction. The three planets will form a triangle, with each roughly two degrees from the other. Your pinky finger held at arm’s length is about one degree wide. Here is what they will look like about thirty minutes after sunset on Saturday, Sunday and Monday nights (May 25, 26 and 27, 2013).
In each image, the large blue dot is Venus (the brightest of the three), the large yellow dot is Jupiter (next brightest) and the smaller pink dot is Mercury.
Venus and Mercury are closer to the sun that is the Earth, and Jupiter is much farther away. The apparent proximity of these planets is a matter of perspective, of course. Here is a view from above the solar system that shows their positions relative to the Earth. You can see how they will appear close to each other in our sky even when they are millions of miles apart.
Mercury and Venus will continue to climb in the sky in the days to come while Jupiter sinks into the sun’s glare, so enjoy this while you can!
How many stars can you call by name? Unless you are a devotee of the night sky, the number will likely not require more than one hand to count. Betelgeuse perhaps, simply because its pronunciation brings to mind a movie starring Michael Keaton. Polaris if you remember that it is the North Star. Alpha Centauri if you know that it is our nearest stellar neighbor beyond the sun. Any more?
Have you wondered about how these stars are named? You might guess that some names are ancient, bestowed upon the brightest stars visible throughout human history. But what about something like SAO 101729, or HD 2341? Did you know that Betelgeuse is also known as Alpha Orionis, HD 39801, SAO 113271 AND GSC 129:1873? Let’s back up a little and see if we can make some sense out of this scrambled mess.
Read more ›