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Comet Tempel 1

Astronomy Questions & Answers

What is the most distant human-caused event that’s been easily verifiable with ordinary optics?

Like other amateurs, I observed the brightening of Comet Tempel 1 after it was hit by Deep Impact on July 4, 2005. Was this the most distant human-caused event that’s been easily verifiable with ordinary optics? (I used my 12-inch Dobsonian reflector.) Yes, we think so. The Deep Impact collision…

Large and Small Magellanic Clouds

Hobby-based Q&A

Why are the Large and Small Magellanic Clouds not listed among the Caldwell objects?

Why are the Large and Small Magellanic Clouds not listed among the Caldwell objects? They are also not given in Stephen James O’Meara’s book The Messier Objects in the list of 20 spectacular non-Messier objects nor among O’Meara’s 20 spectacular non-Caldwell objects in The Caldwell Objects. Are they too bright?…

Venus 7 days from inferior conjunction, imaged by Damian Peach.

Hobby-based Q&A

Is it possible to see the crescent of Venus?

Is it possible, with better than normal eyesight, to see the crescent of Venus? That question has been controversial, but in fact some people can. The rough rule of thumb is that someone with excellent vision can just resolve two image elements 60 arcseconds (60") apart. At times, this is…

Take a walk on the wild side

Astronomy Questions & Answers

How do you convert celestial coordinates for equinox 1950.0 to 2000.0?

I use Burnham’s Celestial Handbook, which gives objects’ celestial coordinates for equinox 1950.0. How do I convert these to 2000.0, the current standard? First off, the difference isn’t great. Fifty years of precession change an object’s right ascension and declination by a total of 0.7° at most (if it’s near…

Astronomy Questions & Answers

How can I see more colors through my telescope?

Nebulae and galaxies invariably look like shapeless, colorless blobs in my 6-inch telescope, a far cry from their spectacular appearance in photographs. If I buy a 12- or 14-inch scope, will I see a dramatic improvement? Would that it were so! A larger telescope will better reveal the shapes of…

Crescent Moon and Venus at sunset

Astronomy Questions & Answers

Could the lunar crescent be seen in a telescope at new Moon?

Is the Moon’s orbit inclined sufficiently that, when it misses the Sun by the greatest amount north (or south), the lunar crescent could be seen in a telescope at new Moon? Probably not. The inclination of the Moon’s orbit to the ecliptic varies from 5.0° to 5.3°. French astronomer André…

Rising Moon

Astronomy Questions & Answers

How is the time of new (or full) Moon defined?

How is the time of new (or full) Moon defined? Astronomically, the Moon is new when it and the Sun have the same celestial longitude. The Moon is at first-quarter phase when its longitude is 90° greater than that of the Sun. The Moon is full when its longitude is…

Dione

Hobby-based Q&A

Do Saturn’s moons cast observable shadows on Saturn?

I’ve seen the tiny black shadows cast by Jupiter’s moons. Do Saturn’s moons cast observable shadows on that planet? Shadow transits of Titan, Saturn’s largest moon, have been seen with a telescope as small as 2 7/8-inch (73-millimeter) aperture. In 1891, two English observers saw the shadow of Rhea on…

Tim Hunter and his telescope

Astronomy Questions & Answers

How Can Amateurs Find Asteroids?

In a 1996 article titled “Hunting Asteroids,” you said a dedicated amateur could discover an asteroid on almost any night using a CCD-equipped 8-inch telescope. Is that still true today? It was easier for backyard observers to discover asteroids a few years ago. Today, massive professional surveys such as LINEAR,…

Hobby-based Q&A

Why doesn't a GPS receiver read longitude 0° 00' 00" while standing on the prime meridian at the Greenwich Observatory?

Why didn’t my GPS receiver read longitude 0° 00' 00" when I visited Greenwich Observatory and stood on the prime meridian? The NAVSTAR satellites of the Global Positioning System can provide your location to an accuracy of 3 meters (10 feet) or better. The coordinates you get are based on…

Comet Halley

Astronomy Questions & Answers

Will it ever be possible to observe Halley's Comet around its entire orbit?

With larger and larger telescopes being built, will it ever be possible to observe Halley's Comet around its entire orbit? It's already being done! The most recent observations of Halley were made on March 6, 7, and 8, 2003, by Belgian astronomer Olivier Hainaut and his colleagues, who acquired simultaneous…

Astronomy Questions & Answers

What defines a planet's north pole?

Uranus is often said to have a retrograde rotation with its axis tilted 98°. Why don’t we say it has a direct spin with the axis tilted 82°? Since 1982, the International Astronomical Union has defined the north pole of a planet to be the pole that lies north of…

SLRs: film (left) and digital (right)

Hobby-based Q&A

Why do people doing CCD imaging often stack five 1-minute exposures instead of taking just one 5-minute exposure?

Why do people doing CCD imaging often stack, say, five 1-minute exposures instead of taking just one 5-minute exposure? Modern digital cameras capture faint astronomical objects with much shorter exposures than their film-based counterparts did, but it still takes an exposure of many minutes to produce a good picture. So-called…

Hobby-based Q&A

Can you get sharper images by stopping down your scope with a cardboard mask?

Old astronomy books often say you can get sharper images on a night of poor seeing by stopping down your telescope with a cardboard mask so it has a smaller aperture. New books don’t mention this. It this a forgotten secret? In my experience, if stopping down a telescope sharpens…

Astronomy Questions & Answers

Will meteor showers be enchanced if you fly 3,000 feet above the ground in an airplane?

I recently got my pilot license. Will meteor showers be enhanced at all for my girlfriend and me in a low-winged Tomahawk airplane, flying 3,000 feet above the ground?There are several tradeoffs to consider. True, you’ll be 1 kilometer closer to the meteors overhead. But most of them flash into…

Hobby-based Q&A

How can we find the Sun's place among the constellations?

How can I find out how our Sun would look among the constellations, as seen from a nearby star? What made me curious was a painting by space artist David Hardy that pictured the Sun as an extra star in Cassiopeia. Fancy planetarium projectors produce such scenes, but you can…

Astronomy Questions & Answers

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).…

Newtonian

Hobby-based Q&A

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…

Full Moon

Hobby-based Q&A

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

Astronomy Questions & Answers

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.…

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