SUNSET: 
How do astronomers accurately determine wobbles in a star's motion?
The discovery of planets around other stars is based on wobbles in the stars' motions. Don't you have to measure from a stationary point in space to accurately determine this/ Isn't there an added wobble because Earth rotates on its axis and travels around the Sun? Yes, Earth's rotation and…
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.…
A Field Guide to Supernova Spectra
With this kit, you're ready to identify stars that explode.
Reporting and Validating a Nearby Supernova
The next time a massive star explodes in the Milky Way, it will cause a mad scramble among amateur and professional astronomers.
You May Already Have a Supernova Detector
Whether you scan the heavens with your eyes, a film camera, or a CCD chip, you've probably got what it takes to find the next galactic supernova.
The Revival of Amateur Spectroscopy
It has never been easier to explore the fascinating world of astronomical spectroscopy with backyard telescopes.
What Are Celestial Coordinates?
"Right ascension" and "declination" tell you where your telescope is pointed in the sky. But what do they really mean?
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…
Finding the Next Nearby Supernova
Somewhere in our galaxy a time bomb is ticking down. When the next supernova blows up, will you be ready?
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.
Do error bars have to overlap the line of best fit?
You often print graphs in which data points have error bars that are too short. About a third of the error bars don’t overlap the line of best fit. So which is wrong? Neither! When it comes to describing statistical uncertainty, such as drawing an error bar, the usual measure…
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…
What's the density of the black hole in galaxy M87?
On page 20 of the March 2004 issue, you say the 3-billion-solar-mass black hole in the center of the galaxy M87 has an average density about that of air. I would love to understand how this makes any sense. The diameter of a black hole scales directly with its mass.…
