SUNSET: 
How could an astronomer living on the far side of the Moon verify Earth existed?
How could an amateur astronomer who lived her whole life on the far side of the Moon verify that Earth existed? Well, not by tuning in episodes of reality TV. Since the Moon has virtually no atmosphere, there is no mechanism (like ionospheric skip) by which radio signals from Earth…
What was the cloud spotted near the western horizon August 31, 2004?
Around 9 p.m. on August 31, 2004, I saw a bright patch of light about half the size of the Moon near the western horizon. It moved slowly upward and fluctuated somewhat in brightness. Through an 8-inch Schmidt-Cassegrain telescope here in New Bloomfield, Pennsylvania, there were two points of light…
Is it possible to have no full Moon in February during a leap year?
Everyone knows there can be two full Moons in a month. Is it possible to have no full Moon in a February containing 28 days? Yes, but only about four times in a century. This happened in 1999 and will next occur in 2018, assuming the phases are expressed in…
How did early astronomers calculate accurate solar system positions?
In the pre-computer age, say 50 years ago and back, how did astronomers calculate accurate positions of the Sun, Moon, and planets for predicting an eclipse or a transit of Venus? They did it by hand, with the help of numerical tables. These weren’t the trigonometric and logarithmic tables you…
How can I spot satellite triads?
While binocular observing from Northern California on August 19, 2004, at 6:33 Universal Time, I picked up a trio of satellites moving from the northwest to overhead and passing through Cygnus. I’m sure they were satellites, as all three turned reddish at the same time before disappearing into Earth’s shadow.…
How can an astrophoto shot through a refractor have diffraction spikes on bright stars?
In your Gallery department (S&TSeptember 2004, page 144), you had a nice image of the star Pollux showing diffraction spikes. That suggests it was taken with a Newtonian reflector, but the accompanying note says a Takahashi refractor was used. Where did the spikes come from? Many imaging enthusiasts like the…
What should I do if my telescope mirror is dusty?
I took my new scope out last night and pointed a flashlight down the tube. My mirror looks really dusty. What should I do? The answer is simple: Don’t shine a light down the tube at night! Seriously, it only makes the dust look a lot worse than it is.…
Will I save money by making my own telescopes?
If I make my own telescope, will I save money? That depends on two things: how large a telescope you’re considering, and how many of the pieces you plan to build versus buy. Given the low prices of today’s commercial telescopes, you will be hard pressed to save money building…
How many daylight hours do you get in a year?
No matter where in the world you live, do you get the same number of daylight hours over the course of a year? No. The equator actually gets fewer hours of daylight than most other latitudes. Any given place would be in daylight exactly 50 percent of a year’s time…
What’s the phase of the Moon during the Perseids?
What’s the phase of the Moon during the Perseids? Use this simple calculation to figure it out.
How Can I Prevent My Finder From Dewing Over?
How do I keep my finder from dewing over when I observe? Your finder should have a light shield (“dewcap”), which you can cover between uses. Or you can purchase an anti-dewing device. This need not be expensive. You probably have a box full of them at home: A simple…
What's my naked-eye magnitude limit?
How can I find out my naked-eye magnitude limit? Count stars inside the Great Square of Pegasus, which is well placed on November evenings. If you can see only two stars within the square, you are reaching visual magnitude 4.6 and your skies are probably light polluted. If you spot…
Can telescopes increase an object’s surface brightness?
I normally can’t see the Triangulum Galaxy (M33) with the naked eye, but it’s easy in a rich-field telescope. So how can you claim (June issue, page 128) that a telescope never increases an object’s surface brightness? The explanation has nothing to do with optics and everything to do with…
Where can I find double star SAO numbers for my Go To telescope?
I want to observe double stars, but my Go To telescope needs their SAO numbers. Where can I get them? SAO numbers come from the Smithsonian Astrophysical Observatory Star Catalog (1966). They aren’t normally used by double-star enthusiasts, who prefer special notations such as ADS 1630, S748, and Krueger 60.…
Could you see astronauts on the Moon?
If there were astronauts on the Moon, could we see them? I get some variant of this question almost every time I show someone his or her first view of the Moon through a telescope, especially at high magnification. The breathtaking sight of lunar craters, mountains, and other features down…
How do you pronounce “Vega” and “Canis Major”?
How do you pronounce “Vega”? “Canis Major”? In 1941 the American Astronomical Society formed a committee of Samuel G. Barton, George A. Davis Jr., and Daniel J. McHugh to consult with astronomers, educators, Arabic scholars, and planetarium lecturers and come up with a list of preferred pronunciations for common star…
Should I wear eyeglasses while observing?
Should I wear eyeglasses while observing? If you are near-or farsighted, with no other eye problems, definitely take them off. You’ll have to tweak the focus, but you’ll see objects in the telescope just as clearly as if you had 20:20 vision. By taking off your glasses you’ll avoid the…
What’s the difference between nebula filters and light-pollution filters?
What’s the difference between nebula filters and light-pollution filters? Nebula filters block out most of the visible spectrum while transmitting the handful of finely tuned colors that emanate from the most luminous constituents of cosmic gas clouds: hydrogen atoms and oxygen ions. Light-pollution filters, by contrast, are designed to block…
How can I get my German equatorial mount to hold its tilt?
My old German equatorial mount won't hold the proper tilt for my latitude. What can I do? Believe it or not, grease the threads and washer of the large bolt that clamps the polar-axis housing to the tripod head. Then tighten it. — Dennis di Cicco
Four Galilean moons shadows
Can all four Galilean moons cast their shadows on Jupiter ’s disk at the same time?No. A triple shadow transit is as good as it gets (S&T: July 2004, page 94). The motions of the three inner moons are gravitationally locked so that, as English astronomer George B. Airy wrote…
