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Astronomy Questions & Answers

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…

FIsh's Mouth or Dementor?

Hobby-based Q&A

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…

Full Moon

Astronomy Questions & Answers

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…

Eyepiece Barrels

Hobby-based Q&A

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.…

Hobby-based Q&A

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,…

Hobby-based Q&A

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…

Moon's skyglow

Astronomy Questions & Answers

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…

Comet Holmes

Astronomy Questions & Answers

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…

Perseid fireball

Hobby-based Q&A

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…

Parallax

Astronomy Questions & Answers

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.…

Plate tectonics explained

Hobby-based Q&A

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…

Twilight view, September 6th

Astronomy Questions & Answers

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…

Hobby-based Q&A

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…

Astronomy Questions & Answers

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…

Porcelain sun dial

Hobby-based Q&A

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…

NGC 4889

Astronomy Questions & Answers

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…

Sunspot AR2192

Hobby-based Q&A

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…

Keck I

Hobby-based Q&A

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…

Moon's far side

Astronomy Questions & Answers

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…

Centaur 2nd-stage rocket

Astronomy Questions & Answers

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…

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