Subject: AstroAlert: Request for Uranus Observations From: Rick Fienberg Date: Mon, 25 Oct 2004 11:49:09 -0400 ================================================================== This Is SKY & TELESCOPE's AstroAlert for Planetary Activity ================================================================== Uranus, whose spin axis is tipped nearly parallel to its orbital plane, alternately turns one pole, then the other, toward Earth as it circles the Sun every 84 years. For the last several decades, Uranus's southern hemisphere has been tipped our way. In 2007 we'll have an equator-on view, and for several decades after that we'll see mostly the northern hemisphere. The last time we had a good equator-on view -- enabling us to observe the whole planet from pole to pole as it rotates once every 18 hours -- was several decades ago. Back then the telescopes, cameras, and techniques available to amateur astronomers were nowhere near as sophisticated as they are today. Thus backyard observers and astrophotographers have an unprecedented opportunity to contribute to professionals' studies of Uranus over the next few years. In a typical backyard telescope, Uranus appears at first glance as a bland blue-green orb surrounded by a few faint moons. But if you look carefully or obtain high-resolution images, you may detect clouds or other features in the planet's atmosphere. Planetary scientist Heidi Hammel (Space Science Institute) is requesting amateur observations and images of Uranus to help identify discrete features in the planet's cloudtops and/or to note any significant changes in the planet's appearance. Hammel notes that in red light, Uranus exhibits a bright band -- a polar "collar" -- encircling the south pole. You can see it in Hubble Space Telescope images shot over the past decade: http://hubblesite.org/newscenter/newsdesk/archive/releases/category/solar%20system/uranus/ In blue light, the polar collar appears as a dark band instead. As we get closer to the equator-on view that's coming in 2007, we'll see less and less of the south polar collar; the planet's south polar region won't look as bright in red light or as dark in blue light as it has in recent years. You should expect to see this, so don't be surprised if it happens. It is a natural consequence of the change in viewing geometry and is not of any particular scientific interest. What will be more interesting is if visual observers and/or astrophotographers start to pick up discrete features (clouds) or evidence for the formation of a polar collar in the planet's northern hemisphere. Note that discrete features will be believable only if they are recorded by more than one observer and/or if they are seen to move across Uranus's disk as the planet rotates. Likewise, confirmation of a north polar collar will require multiple observations. Near-infrared images made with one of the 10-meter Keck telescopes in Hawaii show extensive activity at the same latitude in the north where the polar collar appears in the south, suggesting that a polar collar is indeed beginning to develop in the north. Perhaps it will grow bright enough, or sink low enough in the atmosphere, to become visible in backyard telescopes. (Observations at near-IR wavelengths are sensitive to clouds at higher altitudes than those made at visible wavelengths.) Experienced planetary observers and imagers are encouraged to keep watch for discrete features and/or the formation of a north polar collar on Uranus. Please keep in mind the caveats noted above about confirming the features via multiple observations and/or planetary rotation -- it is easy to be tricked into thinking you've found something that isn't there if all you have is a single observation or picture. Reports of interesting features and/or activity that changes the telescopic appearance of Uranus should be sent by e-mail to Richard Schmude, Remote Planets Coordinator for the Association of Lunar and Planetary Observers (ALPO). His e-mail address is schmude@gdn.edu. Please make sure your report indicates the equipment used and the dates and times (including time zone) of your observations or images. If you're capturing images, the best way to note the orientation of Uranus is to take one image that shows the moons swarming around the planet, followed immediately by a closeup of Uranus itself -- without rotating the camera between exposures. Take care not to overprocess your images; the less sharpening and colorizing, the better. And if you use any filters with your eyepiece or camera, please note the wavelengths they transmit. Uranus spends 2004 in Aquarius. A finder chart appeared on page 107 of the April 2004 issue of Sky & Telescope and is available on the magazine's Web site: http://SkyandTelescope.com/observing/objects/planets/article_1221_1.asp You can get a detailed physical ephemeris for Uranus, one that specifies the orientation of its equatorial plane with respect to Earth as well as the positions of its brightest satellites for any date and time, from NASA's Ames Research Center: http://ringmaster.arc.nasa.gov/tools/ephem2_ura.html Thanks, good luck, and clear skies! -- Rick Fienberg Editor in Chief, Sky & Telescope Chair, AAS Working Group for Professional-Amateur Collaborations ================================================================== AstroAlert is a free service of SKY & TELESCOPE, the Essential Magazine of Astronomy (http://SkyandTelescope.com/). This e-mail was sent to AstroAlert subscribers. 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