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.
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“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.
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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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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.
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My wife and I returned a week ago from a trip to Iceland to see the Northern Lights and some of the scenic wonders of this far-north country. We did see the lights, and they were a magnificent sight! Although we went out every night but one (jet lag and regular nightly expeditions until 2 am required one night of recovery), it was not until our fifth night there when we had all but abandoned hope that the aurorae began to dance for us. To get those gorgeous pictures you see online requires a more expensive camera than ours! Nonetheless, we did get some pictures even though the brightest display was in a light-polluted restaurant parking lot. (Picture of Eyjafjallajökull eruption from Wikimedia Commons, picture of Jane and Neal Sumerlin by Robert Naeye, all other pictures by Jane Sumerlin.)
Even if we had not seen the lights, it would have been a wonderful trip. Iceland is an other-worldly place of great beauty. It truly feels at times as though you are on another planet. The mid-Atlantic rift valley that separates the Eurasian and North American tectonic plates runs right across the island.
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My wife and I will be traveling to Iceland later this week, hoping to see the Northern Lights. There are many astronomical phenomena that don’t require travel, but for the few that do, there are plenty of travel agencies waiting to accommodate you. When we traveled to the South Pacific in 2009 to see a total solar eclipse, it was with a group organized by Sky and Telescope magazine. This trip is also under the auspices of Sky and Telescope, which insures that I will be around people whose enthusiasms match mine. In other words, astronomy nerds.
Why Iceland? And why now? I posted earlier about aurorae, and here I want to give a basic primer in the form of a question-and-answer session.
What are aurorae?
These are glowing lights in the sky caused by charged particles colliding with atmospheric atoms. These particles come mostly from the sun and are trapped in the Earth’s magnetic field. They impart energy to the atoms; when the atoms return to a lower-energy state, they emit light. The aurorae can take the form of a generalized sky glow or of sharply defined features that look like waving curtains. The most we ever see at the latitude of Lynchburg (37.5° N) is this generalized glow when the sun is especially active and the region in which aurorae are most active shifts farther south. When I have seen it, it looks like a late sunset or a fire on the northern horizon.
Aurorae are best seen at high latitudes, either very far south or very far north. For someone living in the United States, Iceland is a lot more accessible than the southern equivalent, which is the Antarctic Peninsula. Aurorae mostly occur in a band called the auroral zone, a ring centered on the Earth’s magnetic (not geographic) pole. Here is a “weather forecast” of the ring from last year, courtesy of NOAA (National Oceanic and Atmospheric Administration—your tax dollars at work again).
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This week, Comet PANSTARRS will be a naked eye object for observers in the northern hemisphere. But you need to be quick–it is low on the western horizon, close to the sun. If you are too early, the sky is too bright to see it. If you are too late, it will have already set. Fifteen to thirty minutes after sunset is the time to start looking. A pair of binoculars may help you spot it. Here is a helpful graphic from our friends at NASA, among the few government agencies people actually like.
It reaches its closest approach to the sun today (March 10), and moves farther away after that. If you look at the diagram, you can see that it also moves farther north each day. PANSTARRS has been visible in the southern hemisphere for some time now, but is only coming into view for those us north of the equator in recent days. This image may help explain why.
The comet is moving from bottom to top (south to north) in this view, which is along the plane of the solar system.
Finally, what’s up with that weird name? Comets are named for their discoverers, so we have perfectly understandable names like Comet West, Comet Hale-Bopp (joint discovery) or even Comet Shoemaker-Levy 9 (the ninth joint discovery by these folks). Increasingly, however, comets are being discovered by automated surveys dedicated to the task. Pan-Starrs stands for Panoramic Survey Telescope and Rapid Response System. Based in Hawaii, where about 75% of the entire sky is visible, its cameras can image all of that in about a week. These images can be compared to the previous ones, and any change will reveal a solar system object (close enough so that its motion is detectable) such as an asteroid or comet. It’s operated by the Air Force, and its main purpose is to detect possibly hazardous Near-Earth Objects. Every once in a while we get a nice bonus!
Most people my age who have wound up in some sort of a science-related career (and many who have not) can trace their excitement about the subject to the space programs of the late 1950s and 1960s. I’m no exception. With advance warning that you will see a scary picture of the 14-year-old me, you can read about some of that here.