61–80 of 188 results

Astronomy Questions & Answers

Why Do Stars Twinkle?

Though it wouldn’t work so well in the nursery rhyme, a star’s twinkling actually has a technical term, astronomical scintillation: the effect of our planet’s atmosphere on starlight.

Astronomy Questions & Answers

Asteroids: What Are They and Where Do They Come From?

Asteroids are rocky objects leftover from the solar system's formation, found primarily in the asteroid belt, a region of the solar system in between the orbits of Mars and Jupiter.

Comet ISON (C/2012 S1)

Astronomy Questions & Answers

Comets: What Are They? Where Do They Come From?

Comets are suspected to be remnants of planet formation in the solar system about 4.6 billion years ago and primarily originate in the Kuiper Belt and the Oort Cloud.

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.

Astronomy Questions & Answers

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.

Astronomy Questions & Answers

How Many Planets Are In Our Solar System?

There are eight planets in the solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

Space weather

Astronomy Questions & Answers

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.

NASA's solar system

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.

Science-based Q&A

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.

Big Dipper photo

Hobby-based Q&A

How far away are the stars I see through my telescope?

The faintest stars I can see in my 4-inch refractor are 12th magnitude. If one of these stars is just like the Sun, how far away is it? The Sun would be magnitude 12.0 if it were 880 light-years away. That’s not very far in the grand scheme of the…

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…

Jupiter with two moons and three shadows on its face

Hobby-based Q&A

Is it possible to detect Jupiter's satellites with the unaided eye?

I’ve heard it might be possible to detect Jupiter’s satellites with the unaided eye if Callisto and Ganymede appear together when Ganymede is at greatest elongation from Jupiter. Will this happen anytime soon? Jupiter is now setting soon after sunset. But three times in 2008, Texans (and North Americans generally)…

Astronomy Questions & Answers

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…

Schmidt-Cassegrain

Astronomy Questions & Answers

Is obstruction of less consequence for photography than for visual observing?

Some of the best images of planets are taken with Schmidt-Cassegrain telescopes, yet people often say that the large central obstruction makes this design ill-suited for planetary observing. Is the obstruction of less consequence for photography than for visual observing? Do CCDs and digital cameras make the central obstruction less…

Saturn and Mars hug the ecliptic

Astronomy Questions & Answers

Why doesn't S&T produce a star atlas with mirror-image charts?

Why don’t you produce a star atlas with mirror-image charts? It would be of immense value to the many observers who use a star diagonal on their telescopes. It’s a great idea in theory, but not in practice. Here’s why: · economics. Printing two versions of an atlas would double…

Hobby-based Q&A

How can a telescope have an f/ratio of f/42?

I was amazed at Jim Melka’s beautiful picture of Mars on page 136 of the January 2006 issue but puzzled by the caption, which said that he used a 12-inch reflector at f/42. How is this possible? Knowing that a telescope’s f/ratio is its focal length divided by its aperture,…

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…

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