94 results
Spokes in Saturn's rings

Astronomy Questions & Answers

What happened to the "spokes" in Saturn's rings?

In 1979 the Voyager spacecraft revealed “spokes” in Saturn’s rings. Yet recent images from Cassini have shown no spokes. What happened to them? Those spokes have kept planetary scientists scratching their heads for decades. It’s thought that the spokes are radial fingers of dark, extremely fine dust particles that become…

Alpha, Beta, and Proxima Centauri

Astronomy Questions & Answers

What date were the two principal stars of the Alpha Centauri system last known to be closest to each other?

On what terrestrial date were the two principal stars of the Alpha Centauri system last known to be closest to each other in space? According to the orbit recently published by Belgian astronomer Dimitri Pourbaix, α1 and α2 Centauri were closest in space (at periastron) in early August 1955, and…

Science-based Q&A

If you combine the magnitudes of all visible stars, how bright a star will you come up with?

Just wondering. . . . If you combine the magnitudes of all visible stars (down to 6th magnitude), how bright a star will you come up with? About 9,000 stars are brighter than magnitude 6.5, the traditional criterion for naked-eye visibility. Their combined magnitude is almost exactly –5, which is…

Science-based Q&A

If you lived on Saturn, would its rings be visible from the equator or the poles?

If I lived on Saturn, would its rings be visible from the equator or the poles? Above the cloudtops and neglecting refraction, geometry dictates that you’d see nothing from the poles. As you moved toward the equator, the bright A ring would start coming into view at latitude 66° (roughly…

artist's impression of a black hole

Astronomy Questions & Answers

What would happen if I fed animatter into a black hole?

What would happen if I fed animatter into a black hole? Could this be a treatment to get rid of black holes? No. Antimatter has positive mass just like ordinary matter, so the black hole would merely get larger and heavier. Whatever fireworks happened inside the hole, if the anitmatter…

Titan steals the show

Astronomy Questions & Answers

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…

Cosmology

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.

Light curves by class

Astronomy Questions & Answers

Why Are There No Green Stars?

There are red stars, orange stars, yellow stars, and blue stars. Why no green stars?

Apophis and Earth in 2029

Astronomy Questions & Answers

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…

Science-based Q&A

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…

Twisting the night away

Astronomy Questions & Answers

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…

Astronomy Questions & Answers

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…

M87

Astronomy Questions & Answers

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.…

Stand-out star on the rise in December

Astronomy Questions & Answers

Why are the stars so far away?

Why are the stars so far away? That question has a real answer: Because if the stars were much closer, Earth wouldn’t exist, and we wouldn’t be here to ask.

1 3 4 5
Advertisement
Advertisement
Advertisement
Advertisement