SUNSET: 
What determines a moon's atmosphere? (Why is Titan's atmosphere so dense?)
Why is it that Saturn’s moon Titan has a dense atmosphere, yet Jupiter’s Ganymede and Callisto (about the same size as Titan) do not? Blame it on their parent planets. All three moons are a mixture of rocky materials and water ice, and the crystalline structure of ice is particularly…
Why Do Bright Stars Look Bigger?
If stars appear as mere points, as we’re always told, why are some stars big and some small in every image I’ve ever seen? Photography does strange things to stars. In fact, the sky on photographs looks rather different from the sky we see visually (S&T: June 2004, page 128).…
Can you adjust a f/7.7 spherical mirror to act like a f/8.0 parabolidal mirror by racking the focus farther out?
My 114-millimeter (4.5-inch) Newtonian reflector came with an f/7.7 spherical mirror. I can purchase a 114-mm f/8.0 paraboloidal mirror. Can I simply adjust for the 34 mm of added focal length by racking the focuser farther out, or should I extend the main tube? Either way, is the upgrade worth…
Where was the Big Bang located?
The commonest misconception about the Big Bang is that it happened at some particular spot in preexisting empty space.
What was that flashing light in the sky?
I'm new to astronomy (1½ months) and I live in New Jersey. Last night, July 31st, I saw a bright planet (I assume Jupiter) in the southwestern sky, and just below it what looked like an airplane with a flashing red tail marker — but it never moved. When I…
Would a large concave mirror suffice for low-power views of extended deep-sky objects?
A large concave mirror, even of low quality, has lots of light-collecting power. Would such a mirror suffice for low-power views of extended deep-sky objects, even if it didn't show stars as neat dots? For example, a 20-inch plastic mirror might be fairly inexpensive. My 7th-grade science teacher once let…
Were stars artistically depicted with diffraction spikes before the invention of the Newtonian reflector?
Were stars artistically depicted with diffraction spikes before the invention of the Newtonian reflector? If so, why? Stars were being drawn with points or spikes long before Isaac Newton announced his reflecting telescope in 1671. Just look at early works of art, flags, ancient coins, and the charts of the…
Why Are There No Green Stars?
There are red stars, orange stars, yellow stars, and blue stars. Why no green stars?
Why aren't Earth's night skies more colorful?
Why are Earth's skies so boring? You see pictures of galaxies, nebulae, clusters, etc., but they're always far away. Why couldn't Earth have been in the middle of a colorful nebula or some other non-boring zone of space? Celestial photos show what things would look like if your eyes were…
Where did the 1 1/4-inch standard size for eyepiece barrels come from?
Where did the 1 1/4-inch standard size for eyepiece barrels come from? This barrel size was adopted shortly before 1890 by John A. Brashear in Pittsburgh, Pennsylvania, says Bart Fried of the Antique Telescope Society. Then W. & D. Mogey of Plainfield, New Jersey, and other firms followed suit.…
Would a perfectly reflecting full Moon be just as bright as the Sun?
I've read that the full Moon has a magnitude of about -13 and an albedo of about 3%. That implies that if the lunar disk reflected 100% of sunlight it would appear more than 30 times as bright, or about magnitude -17. But since it has the same angular diameter…
Will asteroid 99942 Apophis eclipse the Moon when it passes by?
When I heard that a 300-meter asteroid will approach Earth at a distance of only 18,000 miles in 2029, I figured it was time to break out the old slide rule. Wouldn't an object that big and close be able to eclipse the Moon, if it should pass in front…
What is the unfamiliar star in Johnny Horne's image of the Horsehead Nebula?
While looking at Johnny Horne's recent image of the Horsehead Nebula (September issue, page 65), I glanced up at my own picture mounted on the wall and suddenly noticed a "star" in Johnny's image that does not exist in this part of the sky. It must be a passing asteroid,…
With an associate's degree in electronics and computer technology, what are your chances of getting a job in astronomy?
I've been an active amateur astronomer for more than 10 years and would like to turn my hobby into a career. With an associate's degree in electronics and computer technology, what are my chances of reaching this goal?If you define a career in astronomy broadly enough, and if you want…
How does the Moon's phase affect the skyglow of any given location, and how many days before or after a new Moon is a dark site not compromised?
How does the Moon's phase affect the skyglow of any given location? How many days before or after a new Moon is a dark site not compromised? The answer is complicated because the Moon's glow is even more directional than light pollution. Skyglow is several times brighter near the Moon…
Does a comet's tail (or lack there-of) tell us what direction it's heading?
When Comet Holmes was heading away from Earth, we on Earth didn't see an angled view of the comet's tail. Was it tailless because of its motion? That is, would a comet also appear tailless if it were approaching, with Earth right in its path? It's impossible to tell where…
How much space debris falls into Earth's atmosphere every year?
Has anyone ever calculated the combined tonnage of meteroids and space debris falling into our atmosphere yearly? Yes, but it's hard because different methods are needed for different particle sizes. Ground radar and exposed spacecraft surfaces are best for detecting the very smallest bits, whereas photographic surveys have been used…
Should you use light-years or parsecs for astronomical distance?
You give astronomical distances beyond the solar system in light-years, but professional astronomy papers use parsecs. Which is preferable? Light-years, no question! Here’s how I see it. The parsec (which equals 3.26 light-years) is defined as the distance at which a star will show an annual parallax of one arcsecond.…
Did that earthquake off the coast of Sumatra alter Earth's rotation and tilt?
Did the earthquake off the coast of Sumatra that triggered the horrific tsunami on December 26, 2004, alter Earth’s rotation and tilt, as some news stories suggest? The Sumatra earthquake released as much energy as 475 megatons of TNT. That’s some 23,000 times the energy released by the atomic bomb…
When we say a galaxy is 300 million light-years away is that its distance now or 300 million years ago?
When we say a galaxy is 300 million light-years away, is that its distance now or 300 million years ago? Oftentimes, neither! In most cases astronomers try to get a handle on a galaxy’s distance by measuring its redshift: the degree to which the universe’s expansion has stretched its light…
