My first Magazine Sky & Telescope - 02.2019

FROM OUR READERS Right-Sizing Aperture Cosmic Mystery Klaus Brasch • Flagstaff, Arizona I found that Tom Dobbins’s article hit the nail on the head. It highlights the term “empty magniﬁ cation.” This has hit home many times with me. One night, my 10-inch f/4.5 Newtonian apparently outperformed instruments even as large as 60-inch aperture, on the same target, under terrible seeing conditions, taking videos. Computer stacking works well for shifting objects, but not if the seeing prevents details from coming through. Dave Nakamoto • Azusa, California Back to Venus? Shannon Hall’s article “Destination: Venus?” (S&T: Sept. 2018, p. 14) is a real eye-opener, and I sincerely hope that it helps to turn things around for further exploration of our sister planet by NASA. An item that was mentioned only in passing intrigues me. The article mainly concerns volcanism, but it also notes “a giant impact crater.” It is certainly fascinating that the Venusian surface is otherwise largely smooth or volca- nic, indicating relatively recent activity 6 FE B RUA RY 2 019 • SK Y & TELESCOPE over the entire planet that would erase evidence of other impacts. But the fact that there is this one big crater seems to me to merit attention. Wouldn’t further investigation help us determine how recently the inner solar system has been subjected to signiﬁ cant bombardment? I think that has major implications for planetary defense of our home planet . . . and thus offers yet another practical urgency in favor of returning to Venus. Joel Marks Milford, Connecticut Shawn Dilles Vienna, Virginia Old-School Astronomy Jerry Oltion’s Big, Bold, Bright, and Beautiful articles (S&T: Oct. 2018, p. 28 and May 2018, p. 22) have been much more than nostalgic for me. I purchased my 8-inch Coulter Dobsonian in 1990 and have spent many hours sketching bright and beautiful wonders in the sky. As I’ve watched observing decrease and astrophotography increase, I’ve felt like a relic of old-school astronomy. But Oltion’s articles have heartily afﬁ rmed my love and desire for observational sketching without holding it in opposi- tion to photography. I appreciate all aspects of our hobby and am glad to be fully afﬁ rmed in my little corner of it. Pastor Mark Chapman Upsala, Minnesota Guided Tour Jerry Oltion’s “A Tourist’s Guide to the Autumn Highlights” (S&T: Oct. 2018, p. 28) made me want to set up my telescope and wait for nightfall like nothing else I have read in more than 40 years as an amateur astronomer. Jaime Tomé San Juan, Puerto Rico Diverse Interests Antonio Peña’s article on David Malin’s work in color astronomy (S&T: Nov. 2018, p. 30) reminded me of my ﬁ rst and only encounter with this ultimate expert in imagery. While doing a lecture tour in Europe in the 1990s, David visited our local planetarium in Aarhus, Denmark, and I was a bit surprised and also annoyed to learn that he insisted on using his Having used a variety of telescopes at various Northern and Southern Hemisphere sites, I really enjoyed Tom Dobbins’s analysis of the optimal tele- scope aperture for lunar and planetary observing (S&T: Nov. 2018, p. 52) and concur with his overall conclusions. However, a number of other factors also come into play. As with real estate, location really makes a difference. For p It’s hard to beat the views with the 24-inch Clark refractor at Lowell Observatory. instance, that elite group of amateur solar system imagers (Christopher Go, Damian Peach, and Leo Aerts, among others) works mainly at low elevation near seas and oceans, far removed from major mountains. Hence, they frequently enjoy atmo- spheric inversions or smooth laminar ﬂ ow air currents. Often as well, haze and high humidity prevail at such sites, with diminished transparency but very steady seeing. The best seeing conditions I’ve experienced over the years were at Mt. Wilson Observatory, the Atacama Desert, and Mount Pinos in California. While these are arid mountain locations, they border the Paciﬁ c Ocean and hence enjoy frequent westerly laminar air ﬂ ow. In contrast, at my current location east of Flagstaff, where dark, crystal-clear skies and superb transparency dominate, seeing is often rather poor. That’s ideal for deep-sky but rarely for lunar and planetary observing. Still, while 12- to 16-inch-aperture telescopes may be best all-around as Dob- bins attests, size still matters. Under comparatively rare superb seeing conditions at Lowell Observatory, the venerable 24-inch Clark telescope outperforms smaller- aperture instruments hands down every time. I’ve been reading your magazine for over 40 years and have always appreciated the clear, crisp, and accurate science writing. But my appreciation hit a new high with David Nakamoto’s article on BL Lacertae objects (S&T: Sept. 2018, p. 30). This is one of the best articles I have ever read, combining clarity, accu- racy, and good organization with an underlying mystery tale to solve.

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