[分享] 《天空和望远镜》网站预报的火星大冲观测图和照片。

August 22, 2003 | On the night of August 26–27 Mars will pass closer to us than it has in nearly 60,000 years. More precisely, the red planet will be 34,646,418 miles (55,758,006 kilometers) from Earth, measured center to center, at 5:51 a.m. Eastern Daylight Time on the 27th. But for all practical purposes, Mars will appear just about as big and bright for several weeks.
This proximity makes Mars look like a breathtakingly bright "star" in the late-evening sky. You can't miss it! For the remainder of August and all of September, Mars shines many times brighter than any other star in the summer sky. Anyone can see it, no matter how little you know about the stars or how badly light-polluted your sky may be. In late August, look for Mars glaring like a bright orange beacon low in the southeast at nightfall, and higher later in the night. In September it's high up as soon as twilight fades. By midnight Mars is at its highest, shining in the south. Most people will notice the planet's fiery yellow-orange hue, which is due to the rust-like iron compounds in Mars's surface

There has been some confusion over exactly how much of a record this Mars passage is setting. Sky & Telescope senior editor Roger Sinnott got to the bottom of the matter, finding 57,617 BC to be the correct date when Mars last came this near to Earth. That was 59,619 years ago (taking into account that there was no "year zero" between 1 BC and AD 1). For the full story, see "A Mars Record for the Ages". We won抰 have to wait as long for this year's record to be broken: Mars will once again be so close on August 28, 2287.

Mars was nearly this close in 1988, and for all practical purposes it looked much the same as now. That year it reached an apparent diameter of 23.8 arcseconds as seen in a telescope; this year it tops out at 25.1 arcseconds wide (the angular size of a penny seen at a distance of 500 feet). And Mars will make another good pass by Earth in October 2005, appearing 20.2 arcseconds wide.

Even at its nearest, Mars is challenging to study in a telescope. Even at moderately high magnification, it appears as only a small, bright ball with subtle dark markings, the bright white South Polar Cap (now shrinking in the warmth of the Martian late spring), and perhaps white clouds rimming some of the planet's edges. The brightest yellow areas are deserts covered by fine, windblown dust. The dark markings are terrain displaying more areas of bare rock (much of it ancient lava flows) or darker dust. Mars rotates every 24½ hours, so you can see it turning in just an hour or two of watching.

To see much detail on Mars, you抣l need at least a moderately large telescope with high-quality optics. (For the lowdown on how to select a telescope wisely, see "Choosing Your First Telescope".) You'll also need to wait until Mars rises high in the sky, well above the thick, murky layers of atmosphere that hug the horizon. And the "seeing" must be good — that is, the tiny heat waves that constantly ripple through the atmosphere should be minimal. These waves cause highly magnified telescopic images to constantly shimmer and fuzz, but the quality of the seeing changes from night to night and sometimes from minute to minute.

More about Mars and its unusual close approach is in the June, July, and August issues of Sky & Telescope and online in "Mars at Its All-Time Finest".

夜晚火星的天空位置：晚上10点向东南方看那颗最亮的橙红色星。

The orbits of the Earth (blue) and Mars (red) around the Sun. Mars moves in a noncircular orbit, and it will be closest to the Sun almost precisely when Earth moves past it on August 27th. On that date at 5:51 a.m. Eastern Daylight Time, the two planets will be only 34.6 million miles apart — their closest pairing in nearly 60,000 years. The Sun and planet disks are not shown to scale. S&T illustration by Steven Simpson

Seen through a backyard telescope, Mars displays a mottled bright and dark appearance. Also seen is its white south polar cap, consisting of frozen water and carbon dioxide ("dry ice"). This August 2nd image is a composite of about 500 frames of video shot with a Celestron 14-inch telescope and a PlanetCam from Adirondack Video Astronomy. Courtesy Johnny Horne.

8月2日Johnny Horne使用Celestron 14英寸镜子接 Adirondack Video Astronomy出品的行星摄像头拍摄500桢画面叠加而成。

14英寸的望远镜还算是小望远镜？
这照片看来没有香港同好拍的好。

大望远镜一般是指天文台使用的口径在一米以上的专业望远镜。

但原文好像没说是小望远镜，只是说”a backyard telescope”，是否译作后院的望远镜？
s&t应该是面向业余爱好者吧，如果以专业的角度看，那所有天文爱好者用的望远镜都是小望远镜了。

尤其8英寸的到16英寸的镜子都是在青少年宫和业余天文台中使用频率较高的普及型小望远镜。前几日在论坛上贴过的那个西班牙天文摄影家的“小望远镜拍摄的火星”你还记得吧，他使用的望远镜口径是203mm的。此外你也可以很容易找到这样的英文书籍：《小望远镜观测指导》，看看里面说的小望远镜是不是只是包含60mm左右的镜子。而且我并不是总按照原文来翻译，一般会根据一些常识性问题来做些解说。其实也没有必要在一些支根末节上钻牛角尖吧，当然如有不妥还望海涵。其实有些叫法是约定俗成的，小望远镜和大望远镜只是业余级别和专业级别的代称，下面给你看篇报道我想你会更能理解的：


Wellesley's Small Telescope Contributes To Big News About Asteroids
WELLESLEY, Mass. -- As a new astronomy department instructor at Wellesley College last fall, Stephen M. Slivan proved that small telescopes can yield big discoveries. In fact, his startling findings were reported in Nature magazine this fall.
"The science results reported in Nature reveal a phenomenon that was never before even predicted, namely that some clusters of asteroids have spin directions that are correlated," Slivan said. "All prior theories suggest that they should be random."

The findings have potentially far-reaching impact.

"The main scientific goal is to find clues to help us understand how our solar system, and Earth in particular, originally formed and subsequently evolved into what we see today," Slivan said. "A second aspect of interest is to study specifically how asteroids break apart in collisions, which would be a useful thing to know when deciding how to deal with the future possibility of an Earth-crossing asteroid someday colliding with our planet."

Slivan says Wellesley's small telescope contributed to the findings.

"Data I obtained using Wellesley's Whitin Observatory 24-inch telescope last November, only about two weeks after I began teaching here, are included in the data from which the results were derived," he said. "The fact that small telescopes in the Northeast (Wellesley's 24-inch, MIT's 24-inch and Colgate's 16-inch) can produce results meriting publication in Nature defies the 'common knowledge' that only big observatories at mountaintop sites can do world-class research."

Another factor in his study belies another fallacy: that first-year college students do not contribute to important research. At Wellesley, they most certainly did.

"Erin Marie Collins, then a first-year student, availed herself of the opportunities for early involvement in real research, encouraged and supported by the Astronomy Department faculty, and directly assisted me in obtaining the Wellesley data by observing with the 24-inch telescope," Slivan said. "Our lightcurve from that night appears in the Nature article. The details of the observing program will appear in a longer second manuscript currently in review at the planetary science journal Icarus."

Collins, of Smyrna, Ga., is excited about her contribution. "At the time, I had no idea that that what I was observing would be such a big deal," she said. "It's thrilling to know that I contributed to such a significant project." Now a sophomore majoring in psychology and minoring in astronomy, Collins continues to work at the Wellesley observatory using the 24-inch telescope this fall along with other students.

Here's a summary of Slivan's findings, in his own words:

"My research is a long-term observational study of the largest members of the Koronis family of asteroids. Asteroids are small, rocky bodies in the solar system that orbit the sun and are thought to be bits of material that never formed into a planet. They offer us clues about the conditions under which the solar system, including Earth, originally formed.

"Even though asteroids seem to be primitive material, we expect that they've not remained completely unchanged since the solar system originally formed. Collisions between asteroids have probably played a major role in creating the asteroids that we see today from larger objects that existed in the past. When a large asteroid is shattered and dispersed by a collision, the resulting fragments can form an 'asteroid family' whose members all have nearly identical orbits. To some extent we can think of the family as the outcome of a huge natural collision experiment, much more energetic than anything that humans have ever experienced. By studying the sizes, shapes and orientations of the pieces (that is, the family members) we can better understand what happened in the collision. The hope is that, eventually, this knowledge could be applied to the asteroids as a whole to help figure out how the present asteroid population is related to the original population.

"One of the most populous of these groupings is the Koronis family, whose members orbit among the main belt asteroids between Mars and Jupiter. Determining the shapes and orientations of Koronis family members from Earth presents a challenge because they're far enough away that even the largest members (diameters of about 40 km) are too small to appear as anything but a small dot of light, just like a faint star. The trick is to take advantage of the fact that asteroids in this size range tend to be irregularly shaped, exhibiting a change in brightness as they rotate and alternately present end-on and side-on views. A plot of these brightness changes over time is called a lightcurve. By observing lightcurves of an object over many years as the viewing geometry changes, it's possible to get enough data to work backwards and deduce information about the object's shape, the orientation of its spin axis and which way it's spinning on that axis.

"rior to 1992 only a handful of Koronis family lightcurves had been recorded, far fewer than needed to do shape and spin solutions. Since that time I've been observing more lightcurves, and by the summer of 2001 I'd accumulated enough new data that I could run shape and spin solutions for nine of the largest members of the Koronis family.

"The results proved to be quite a surprise. Theoretical models of family formation and laboratory-scale collision experiments both predict that the tremendous amount of energy released in a large asteroid collision yields fragments that randomly spin off into space, but my observations show that, at least for the Koronis family, the spin axes are markedly clustered into only two preferred directions. Even more surprising is that there's an obvious correlation between the two spin orientations and two preferred rotation rates. As of now, current understanding of how families form and evolve has no consistent way to explain how these objects could possibly be aligned in the way they are. In the Nature paper, I very briefly speculate that perhaps secondary collisions after the family-forming collision formed the two observed 'spin clusters,' or perhaps some previously unsuspected dynamical effect can organize randomly oriented spins into the observed groupings."

For more on the Wellesley Astronomy Department and Whitin Observatory, go to http://www.wellesley.edu/Astronomy/.

The full text of Slivan's article can be found on the Nature web site at http://www.nature.com/cgi-taf/Dy ... ature00993_fs.html.

For a summary published by space.com, go to http://www.space.com/scienceastr ... blings_020904.html.

Founded in 1875, Wellesley College has been a leader in liberal arts and the education of women for more than 125 years. The College's 500-acre campus near Boston is home to 2,300 undergraduate students.


Editor's Note: The original news release can be found here.


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其实，我也不是钻牛角尖。只是，专业和业余的角度不同，而我们的论坛主要面向业余爱好者，如果初学者看到小望远镜，以为是一般小口径（业余角度）的望远镜都能有这效果。我认为翻译时也不必说是“小”望远镜了，只需说明口径的大小，更形象和客观。

小望远镜和大望远镜的区别很多天文爱好者都明白，尤其是S&T网站也常这么称呼。我想也没有多少人会认为小望远镜就是60mm或者更小的。当然兄的本意是为那些很初级的爱好者考虑，我想我可以理解你，以后我的解释会尽量更倾向他们的。

对应于小望远镜的，有坐标网和地名，不要那种火星探测器的高分辨率地图，谁能贴上来或上传到我的服务器： ftp://suhuasky.vicp.net up:up