Exoplanet, NASA

Exoplanets

Giant Planets and Wonky Orbits

Kepler-108 is the first system observed with really wonky orbits, which may be a result of giant planets bumping into each other.

Astronomy Questions & Answers

Can Venus ever be far enough from the Sun to appear east of the meridian?

During the Northern Hemisphere winter solstice, when the Sun is farthest south and sets in the southwest, can Venus ever be far enough from the Sun to appear east of the meridian? Yes, but only when viewed from near-arctic latitudes. In late 2008, for example, Venus is the Evening Star…

Totality

Astronomy Questions & Answers

When will the last total solar eclipse occur?

With the Moon slowly receding from Earth, there will come a time when it no longer has sufficient angular size to cover the Sun completely. When will the last total solar eclipse occur? When the Moon’s at its closest and biggest and it can no longer cover the Sun at…

Milky Way Galaxy, NASA / JPL-Caltech

Science-based Q&A

What percentage of our galaxy’s stars move in retrograde orbits?

Do astronomers have any idea what percentage of our galaxy’s stars move in retrograde orbits? The short answer is yes, a very small percentage. But the long answer is more interesting. First, let’s agree what we mean by “retrograde.” If you were to look down on the solar system from…

Astronomy Questions & Answers

How can binary stars orbit each other so fast?

In a News Note (S&T: November 2004, page 16) you described WR 20a, a binary star in Carina with components of 83 and 82 solar masses and an orbital period of 3.686 days. How can two huge balls of gas move so fast? Grab any introductory astronomy textbook and turn…

Alpha, Beta, and Proxima Centauri

Science-based Q&A

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…

Moon's far side

Hobby-based Q&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…

Venus Ring of Light

Hobby-based Q&A

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…

Hobby-based Q&A

Four Galilean moons shadows

Can all four Galilean moons cast their shadows on Jupiter ’s disk at the same time?No. A triple shadow transit is as good as it gets (S&T: July 2004, page 94). The motions of the three inner moons are gravitationally locked so that, as English astronomer George B. Airy wrote…

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