SUNSET: 
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…
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…
Should you set your digital camera to a low or high ISO value in twilight?
When I’m shooting a planetary grouping in twilight, should I set my digital camera to a low or a high ISO value? The easiest way to answer this question is to make test exposures of a skyline during twilight, with or without planets. Try all the available ISO values (analogous…
Are machine-made telescope mirrors better than those made my hand?
Are machine-made telescope mirrors better than those made my hand? In general, no. Making a telescope mirror is a two-step procedure. First you generate and refine the curve in the glass, and then you carefully modify that curve, in the process known as figuring, to give the mirror’s polished surface…
How is the date of Easter determined?
How is the date of Easter determined? The rule most people remember is that Easter falls on the first Sunday after the first full Moon following the March equinox. In practice, Roman Catholic and Protestant churches follow a method of calculation adopted with the Gregorian calendar reform of 1582. The…
Can you use a replica of an 18th century New England sundial in Washington?
I have a museum’s pewter replica of an 18th-century New England sundial. The inscription says it was designed for latitude 42°. Can I use this sundial in Seattle, Washington? The iconic garden sundial, with triangular shadow-casting gnomon and horizontal plate, gives accurate readings at the latitude for which its hour…
What's the most distant object I can see with my telescope?
Is there a more distant object than NGC 4889 (Caldwell 35) that I can see with my 5-inch reflector? Yes, by a factor of 7! Think quasars. NGC 4889 is a member of the Coma Galaxy Cluster, which lies about 300 million light-years away. But the quasar 3C 273 is…
How can you determine a sunsport's size compared to that of Earth?
Turn off the telescope's motor drive (if any). Count the number of seconds it takes for the sunspot to drift past crosshairs or any speck of dust that is visible in your eyepiece. The number of seconds equals the spot's breadth in Earth diameters. The method is approximate. If…
How will you know when you telescope mirrors need re-aluminizing?
I have read that telescope mirrors require periodic re-aluminizing. How will I know when mine needs this? While it’s true that the aluminized surface of a telescope mirror will deteriorate over time, there is no hard and fast rule about how long this will take. Some coatings last only a…
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.…
