Star Struck

How to Point a Telescope

It was a lot simpler in Galileo’s day.

Up and down, left and right, manually controlled—simple, right? Yes, but simpler was not always better, at least until computers came along. But we’re getting ahead of ourselves.

There are two issues to be dealt with here.

  1. Pointing the telescope accurately.
  2. Following the apparent movement of celestial objects so that they remain in view.

Accurate pointing–The first is not a big problem if you are not working with a high-magnification view. A pair of 7 x 50 binoculars which magnify 7 times (the 50 is the diameter of the light-gathering lens in millimeters) can be hand-held and pointed with relative ease. A typical field of view for these binoculars is 7 degrees, and this is 14 times the width of the full moon.

A larger instrument clearly cannot be hand-held, and larger light-gathering elements (whether a lens or a mirror) allow higher magnifications. Here is the view afforded by a medium-power eyepiece in combination with the 20-inch Gilbert telescope at Lynchburg College’s Belk Observatory. This field is about ¼ of a degree across and is indicated by the red circle beside the moon.

FOV for Gilbert

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Ladies and Gentlemen…Voyager Has Left the Solar System!

To boldly go where no one has gone before…

Bigger than Elvis? I would say so.

NASA announced today that the Voyager 1 spacecraft launched 36 years ago has finally entered interstellar space, the space between the stars. This is an epic stage of human exploration. You can read more about it here.

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Full Moons: Not So Super?

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.

Hipparchus at full phase

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?

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Posted in Sky Phenomena, The Moon

Where Do You Build An Observatory?

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!

Annual Mean Number of Cloudy Days Sunrise to Sunset
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Quick Follow-up

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.

Curiosity descent from MRO

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Hurray For Plutonium!

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.

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Flying With Cassini

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!

July 10

July 11

July 12

July 13

July 14

July 15

July 16

July 17

July 18

July 19


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In Saturn’s Shadow

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.

Backlit 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.

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My Favorite Things

“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.

Saturn in a small telescope
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Is Interplanetary Space Too Hot For Humans?

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.
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Posted in human spaceflight, Mars, Solar System, Spacecraft