61–80 of 95 results

Astronomy Questions & Answers

Why do comets have tails?

Comets develop tails as they approach perihelion—the place in their orbits when they are closest to the sun. The sun’s heat causes some of the material in a comet to vaporize, which in turn releases dust particles that were trapped in the ice.

Science-based Q&A

How big is the Sun?

The Sun is more than 330,000 times as massive than the Earth. It has a diameter of nearly 1.4 million kilometers (865,000 miles), and its volume could enclose about 1.3 million Earths.

Space weather

Science-based Q&A

What is the solar wind?

The Sun’s outer atmosphere, the corona, is the source of the solar wind, a steady outflow of charged particles from the Sun.

Eight planets await

Science-based Q&A

What Is the Smallest Planet and Largest Planet in our Solar System?

When it comes to both mass and volume, Jupiter is the largest planet in the solar system, while Mercury is the smallest.

Science-based Q&A

What is a meteor shower?

Meteor showers occur when Earth passes through a stream of meteoric material. The brief streaks of luminescence we call meteors are caused by meteoroids burning up as they pass through the atmosphere.

Astronomy Questions & Answers

Astrology vs Astronomy: What's the Difference?

The practices of astrology and astronomy have common roots, but they have evolved into two separate fields. Astronomy studies positions, motions, and properties of celestial objects. Astrology attempts to study how those positions, motions, and properties affect people and events on Earth.

Science-based Q&A

What is radio astronomy?

Radio astronomy is the study of the universe through analysis of very long-wavelength emission from celestial objects.

Science-based Q&A

What is a Sundog, and How Did "Sundogs" Get Their Name?

Why are "sundogs" called by that name? Bob Johnson / SkyandTelescope.com Photo Gallery Before answering the why question, let me answer the what question that comes before: namely, what is a sundog, or mock Sun, in the first place? A sundog is a concentrated patch of sunlight occasionally seen about…

Saturn on July 18, 2015

Science-based Q&A

Why do the outer, gas-giant planets rotate faster than the inner, terrestrial planets?

Why do the outer, gas-giant planets generally rotate much faster than the inner, terrestrial planets? The reasons why some planets rotate as quickly as they do remain puzzling to planetary scientists. Most studies in this area have focused on the inner planets. Earth and Mars, which accumulated gradually from rocky…

The 12 Planets of Our Solar System

Science-based Q&A

Will all eight planets ever line up on the same side of the Sun?

Will there ever be a moment when all eight major planets are in a straight line on the same side of the Sun? Jean Meeus addresses this in Mathematical Astronomy Morsels (Willmann-Bell, 1997). He points out that you have to start by defining the question precisely. Let’s reduce the problem…

Andromeda Galaxy

Science-based Q&A

Is it true that Andromeda Galaxy is moving toward us?

Is it true that the Andromeda Galaxy is blueshifted and moving toward us? How can this happen in an expanding universe? The Andromeda Galaxy (M31) is indeed approaching us, by about 300 kilometers (190 miles) per second measured with respect to the Sun. If you subtract the Sun’s orbital motion…

2003 UB313 art

Astronomy Questions & Answers

Why are Kuiper Belt discoveries made at aphelion?

Why is it that so many of the recent Kuiper Belt discoveries — including the “10th planet,” 2003 UB313 — have been made while the objects are at aphelion? Timing and luck. Objects that orbit the Sun spend most of their time near the farthest point of their orbits, where…

Astronomy Questions & Answers

How many stars are in the Milky Way?

What is the best educated guess for the number of stars in the Milky Way? I’ve seen figures ranging from “some 20 billion” to “just under 600 billion.” The first seems too low, whereas the latter too high. The short answer is, nobody knows. But your reasoning is sound: 20…

Westerlund 2 as viewed by Hubble's WFC3

Science-based Q&A

What does “true color” mean in a deep-space photograph?

What does “true color” mean in a deep-space photograph? How would a galaxy or nebula actually look to the naked eye from close up? “True color” is how an object would look if you were nearby or were viewing it in a telescope under a dark sky, and if its…

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…

Science-based Q&A

If asteroid 99942 Apophis ever strikes Earth, how big would the crater be?

If the near-Earth asteroid 99942 Apophis ever strikes Earth, how big would the crater be? Apophis (formerly 2004 MN4) ranks at the top of the worrisome-asteroid list. On April 13, 2029 (yes, that will be a Friday the 13th), it will pass only 30,000 kilometers (18,600 miles) from Earth’s surface…

Astronomy Questions & Answers

How large an asteroid could a person jump off?

How large an asteroid could a person jump off? This interesting question goes back to 1952 or even earlier. It turns out that the asteroid must be no bigger than 3.9 v(ρe / ρ) kilometers in diameter, where ρ is the asteroid’s density and ρe is that of Earth in…

microlensing diagram

Science-based Q&A

Why are there two peaks in the light curve on page 97 of the October 2005 issue?

Why are there two peaks in the light curve on page 97 of the October 2005 issue? One might imagine that a planet of the star would produce only one sharp peak on the rounded dashed line. But why two? This is an insightful question, because astronomers who use the…

Milky Way Galaxy, NASA / JPL-Caltech

Astronomy Questions & Answers

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…

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