- General Questions
- When the Sun converts mass to energy, do the orbits of the planets change? (Advanced)
- How long does it take for the Sun's light to reach us? (Beginner)
- Is it possible to measure the temperature of the Sun? (Beginner)
- Do we know everything about the Sun? (Beginner)
- Do asteroids hit the sun? (Beginner)
- If we invented special suits could we ever go to the sun? (Beginner)
- How does the Sun compare to other stars? (Beginner)
- How can the Sun have such a strong gravitational field if it's made of gases? (Beginner)
- Is there sound coming from the Sun? (Beginner)
- Does the Sun have a scientific name? (Intermediate)
- When did people discover that the Sun is a star? (Intermediate)
- Solar Cycle and Sunspots
- What's that dark spot on the Sun? (Beginner)
- What is the solar cycle? (Beginner)
- How many sunspots can the Sun have at once? (Beginner)
- How do solar flares affect airline pilots? (Intermediate)
- What are some of the effects of solar flares on Earth? (Intermediate)
- How do we know that sunspots are associated with the Sun's magnetic field? (Intermediate)
- Does the Sun rotate? (Intermediate)
- How are sunspots formed? (Intermediate)
- Birth, Death and Evolution of the Sun
- Composition
- Interior
- The Solar System
- How likely is it that the Solar System has had or will have a close encounter with another star? (Intermediate)
- Can the theory of formation of the solar system explain all the observables? (Intermediate)
- !How do I make a scale model of the Solar System? (Intermediate)
- What is the size of the Solar System? (Intermediate)
- What are the names of the earth, moon, sun, and solar system? (Beginner)
- What is the evidence supporting the nebula theory of Solar System formation? (Intermediate)
- Where is the supernova remnant that led to our solar system? (Intermediate)
- How are galaxies and solar systems similar? (Advanced)
- Are the planes of solar systems aligned with the plane of the Galaxy? (Intermediate)
- The Sun in the Milky Way
- Observing the Sun
- Why do rays from Sun appear to converge at a point? (Beginner)
- Why does the Sun's apparent path through the sky change throughout the year? (Beginner)
- Why can we see the sun's image before sunrise and after sunset? (Beginner)
- Which way does the sun travel in the southern hemisphere? (Beginner)
- Is the green flash real? (Beginner)
- Why does the Sun appear larger on the horizon than overhead? (Intermediate)
- How do astronomers observe the Sun's interior? (Intermediate)
- Why does the location of sunrise change? (Intermediate)
- Solar Eclipses
- Why can we have solar eclipses? (Beginner)
- How long does a solar eclipse last? (Beginner)
- Will I be able to see the shadow of the Moon streaking towards me in a total solar eclipse? (Beginner)
- Is there a simple formula to calculate solar eclipse timings from any position on Earth? (Intermediate)
- Is it a coincidence that we can have total solar eclipses? Are there other planets which also have them? (Intermediate)
- Will we ever stop having solar eclipses because of the moon's motion away from the Earth? (Intermediate)
- General Questions
- Comets
- Could we send a space mission to a comet? (Beginner)
- When is the next comet due to arrive? (Beginner)
- How many comets are currently orbiting our sun? (Beginner)
- If comets are boiling away, why are there any left? (Intermediate)
- When will Halley's Comet return? (Intermediate)
- When will Hale-Bopp return? (Intermediate)
- Will Comet Elenin (C/2010 X1) affect the Earth on its close approach in Fall 2011? (Intermediate)
- What caused Shoemaker-Levy 9 to split up? (Advanced)
- Asteroids
- Are the asteroids the remains of a planet which broke apart? (Beginner)
- Are there any asteroids on a collision course with Earth? (Beginner)
- Do asteroids hit the Sun? (Beginner)
- How did asteroids form and what is the difference between an asteroid and a comet? (Beginner)
- Do asteroids ever do anything good in the Solar System? (Beginner)
- How are asteroid compositions and classifications determined? (Intermediate)
- How dangerous are the asteroids? (Intermediate)
- Meteors (Shooting Stars) & Meteor Showers
- How can I watch the Perseid meteor shower? (Beginner)
- What are shooting stars? (Beginner)
- What color are meteors? (Beginner)
- Will the Leonid meteor shower go away? (Beginner)
- Why don't skydivers burn up like meteors? (Beginner)
- What was that really big falling star that I saw? (Intermediate)
- What is the typical size of a visible shooting star? (Intermediate)
- Did I really hear a meteor? (Intermediate)
- Do more meteorites fall at low latitudes? (Intermediate)
- How do I maximize my chances of seeing shooting stars? (Intermediate)
- Meteorites
- How can I tell if the rock I found is a meteorite? (Beginner)
- Why is it important to study meteorites? (Beginner)
- What's the biggest meteorite? (Beginner)
- Was I hit by a meteorite? (Intermediate)
- Are meteorites hot or cold when they hit Earth? (Intermediate)
- How many meteorites hit Earth each year? (Intermediate)
- How do we detect incoming meteorites? (Intermediate)
- What do meteorites tell us about life on other planets? (Intermediate)
- The Kuiper Belt and Oort Cloud
- General Questions
- How many Earths fit into the Sun? (Beginner)
- Is the Earth slowly getting larger? (Beginner)
- Where did the name 'Earth' come from? (Beginner)
- How much longer will the Earth last? (Beginner)
- Can we feel the Earth spin? (Beginner)
- What if the Earth rotated twice as fast? (Beginner)
- Did I see the Aurora Borealis as a child? (Beginner)
- What causes the aurora? (Beginner)
- How does melting a material reset its radioactive clock? (Intermediate)
- How do we know the age of the Universe and the Earth? (Intermediate)
- Do the Sun's or Earth's magnetic field reverse? (Intermediate)
- What makes the Earth rotate? (Intermediate)
- Did the Sumerians measure precession? (Intermediate)
- How long has there been water on Earth? (Intermediate)
- Do the Earth's magnetic poles ever change places? (Intermediate)
- Impacts
- What would happen if an impact caused Earth to stop rotating? (Beginner)
- Are there any asteroids on a collision course with Earth? (Beginner)
- What would happen if an asteroid 10 kilometers across hit the Earth? (Beginner)
- Why are there no craters on Earth? Did all the meteorites miss us? (Beginner)
- Did a giant impact cause the Dark Ages? (Beginner)
- What is the biggest crater recorded on Earth? (Beginner)
- Why are craters round? (Beginner)
- How dangerous are the asteroids? (Intermediate)
- Would the biggest airplanes cause tsunamis if they crashed? (Intermediate)
- Will Comet Elenin (C/2010 X1) affect the Earth on its close approach in Fall 2011? (Intermediate)
- Other Catastrophes
- What would happen to us if the sun went out for an hour? (Beginner)
- How long could life on Earth survive if the Sun stopped shining? (Beginner)
- What will happen to life on Earth when the Sun becomes a red giant? (Beginner)
- What would happen if the gravity on Earth was suddenly turned off? (Beginner)
- How will the two black holes that are going to collide affect Earth? (Beginner)
- Will we get sucked into the black hole at the center of the Milky Way? (Beginner)
- How close does a supernova need to be to damage the Earth's environment? (Intermediate)
- Will the sun go supernova in six years and destroy Earth (as seen on Yahoo)? (Intermediate)
- How big a change in the Earth's orbit would be required to destroy all life? (Intermediate)
- How long would it take the Earth to fall into the Sun? (Intermediate)
- What's going to happen on December 21st 2012? (Intermediate)
- What would happen if a supermassive black hole came close to the Earth? (Advanced)
- Will the magnetic field of the Earth reverse its direction in the future? Will this cause problems? (Advanced)
- How long would it take for a mini-black hole to eat the Earth? (Advanced)
- Day-night Cycle
- How does night and day work? (Beginner)
- Is the Sun always up for exactly 12 hours at the equator? (Beginner)
- Why is a day divided into 24 hours? (Intermediate)
- How can I calculate the position or path of the Sun for a given time and location? (Intermediate)
- How do sunrise and sunset times change with altitude? (Intermediate)
- Why doesn't the length of each day change much around the solstices? (Intermediate)
- How is the time of sunrise calculated? (Intermediate)
- How much can the location of sunset differ from due West? (Intermediate)
- Why is twilight short near the equator? (Intermediate)
- How does the location of sunrise and sunset change throughout the year? (Advanced)
- Why doesn't the earliest sunset occur on the shortest day of the year? (Advanced)
- Seasons
- What causes seasons? (Beginner)
- Why does the Earth tilt back and forward once a year? (Beginner)
- Will the seasons change due to precession? (Intermediate)
- What are the "dog days of summer"? (Intermediate)
- What is the significance of the Tropic of Cancer, Tropic of Capricorn, Arctic Circle and Antarctic Circle? (Beginner)
- Climate and Weather
- Why isn't the summer solstice the hottest day of the year? (Beginner)
- What is the hottest time of day? (Beginner)
- How critical is the Earth-Sun distance in maintaining our average temperatures on Earth? (Intermediate)
- Can any comparison be made between spiral galaxies and hurricanes? (Intermediate)
- How would the weather on Earth be different if it were a cube? (Intermediate)
- What makes the wind? (Intermediate)
- Why do airplanes take longer to fly West than East? (Intermediate)
- If the sun went out and our atmosphere froze solid, what color would it be? (Intermediate)
- Orbit
- At what speed does the Earth move around the Sun? (Beginner)
- Does the Sun orbit the Earth as well as the Earth orbiting the Sun? (Beginner)
- Is there a proof that Earth moves? (Intermediate)
- How do you measure the distance between Earth and the Sun? (Intermediate)
- Considering the motion of the Earth, the solar system, and the galaxy, how fast am I moving while lying in bed asleep? (Intermediate)
- How fast does the Earth go at perihelion and aphelion? (Intermediate)
- Can the Sun be closer to the Earth than any planet is to Earth? (Intermediate)
- Is the distance from the Earth to the Sun changing? (Advanced)
- What is the difference between nutation and precession of the Earth? (Advanced)
- How can I find the distance to the Sun on any given day? (Advanced)
- Gravity
- Why don't people walk upside-down on the bottom of the Earth? (Beginner)
- Does your weight change between the poles and the equator? (Intermediate)
- Does gravity vary across the surface of the Earth? (Intermediate)
- Would your weight change as you go underground? (Advanced)
- How close do you have to come to the Earth to be influenced by its gravity? (Advanced)
- General Questions
- Where does the name "Moon" come from? (Beginner)
- What percent of the time can astronomers observe without interference from the Moon? (Beginner)
- How do we measure the size of the Moon and of the Sun? (Beginner)
- How long is twilight on the Moon? (Beginner)
- Does the Moon rotate? (Beginner)
- Is the Moon hollow? (Intermediate)
- Does the Moon rotate? Are there other moons that always keep one face toward their planet? (Intermediate)
- How does the Moon stay "suspended" in the air? (Intermediate)
- Can I buy land on the Moon? (Intermediate)
- Can you fire a gun on the Moon? (Intermediate)
- What happens to a bullet fired on the Moon? (Intermediate)
- Can moons have moons? (Intermediate)
- Can we prove that the Moon isn't hollow? (Intermediate)
- Is the Moon spherical? (Intermediate)
- The Moon Landings
- Observing the Moon
- Why is the Moon so bright? (Beginner)
- What is that ring (or rainbow) around the moon? (Beginner)
- Are there telescopes that can see the flag and lunar rover on the Moon? (Beginner)
- Why is the shadow on the Moon the shape it is? (Beginner)
- Why are the Moon and Sun sometimes orange or red? (Beginner)
- Why is the moon in a different place every night? (Beginner)
- Will the Moon be invisible in 500 million years? (Beginner)
- How can you tell if a crescent moon is preceding or following a new-moon phase? (Beginner)
- How do I explain to my children why the Moon has phases? (Beginner)
- On which days can I see the Moon in the evening / morning and why is this so? (Beginner)
- The Moon and Sun are the same apparent size in the sky. The Moon is moving away from us at 3.8 centimeters/year. Isn't it improbable that we live in an epoch in which they appear the same size in the sky? (Beginner)
- Does the direction of the moon's crescent change through the night? (Beginner)
- Does the Moon look different in the northern and southern hemispheres? (Beginner)
- Why is the Moon higher in the sky in winter and lower in the summer? (Beginner)
- Why does the Moon look big on the horizon? (Intermediate)
- Is it possible to see the full Moon and the Sun simultaneously in high northern latitudes when the Sun doesn't set? (Intermediate)
- How can I find out if the new moon has been sighted? (Intermediate)
- Why do the size and brightness of the full moon change? (Intermediate)
- Are there any new craters on the Moon? (Intermediate)
- How does the position of Moonrise and Moonset change? (Intermediate)
- When can I see the Moon through the hole in the Pantheon? (Intermediate)
- Is the Moon always visible during winter on the North Pole? (Intermediate)
- How does libration allow us to see more than 50% of the Moon? (Advanced)
- Why is the time between two successive full moons different from the lunar synodic month? (Advanced)
- Is the Moon seen as a crescent (and not a "boat") all over the world? Is the same phase of the moon visible from the Northern and Southern hemispheres? (Advanced)
- A line drawn perpendicular to a line through the tips of the horns of the crescent moon doesn't point to the Sun! Why not? (Advanced)
- Lunar Eclipses
- Geology
- The Moon and the Earth
- Are Earth and the Moon "twin planets"? (Beginner)
- How much does the Earth "wobble" on its orbit due to the Moon's gravity? (Intermediate)
- What will happen to Earth's tides as the moon moves away from us? (Intermediate)
- Why are there high tides during a Full Moon? (Intermediate)
- Did the Moon or planets form in a manner similar to that of Earth? (Beginner)
- Are there solar tides? (Beginner)
- Does lunar gardening really work? (Beginner)
- What would happen to the Earth if an asteroid hit the Moon? (Intermediate)
- What would happen if we did not have a Moon? (Intermediate)
- Is the gravitational force exerted by the Earth on the Moon equal to the centripetal force acting on the Moon? (Intermediate)
- The Moon slows the Earth's rotation, but how fast was it spinning billions of years ago? (Intermediate)
- What happens to the Earth as the moon gets farther away and will it ever go away entirely? (Intermediate)
- Why does the Earth only see one side of the Moon? (Intermediate)
- Why are there both high and low tides? (Intermediate)
- Why does the Earth have only one moon? (Intermediate)
- Is the Moon moving away from the Earth? When was this discovered? (Intermediate)
- What would happen if Earth had more than one moon? (Intermediate)
- What would happen if the Moon fell out of its orbit around Earth? (Intermediate)
- What is Earthrise over the Moon? (Intermediate)
- Have astronomers discovered Earth's second moon? (Intermediate)
- Does Mt. Everest cast a shadow on the moon? (Intermediate)
- Does the Mediterranean sea have tides? (Intermediate)
- How close was the Moon to the Earth when it formed? (Intermediate)
- Is Earth-moon tidal friction causing global warming? (Intermediate)
- How do we know the mass of the Earth and the Moon? (Advanced)
- Can other terrestrial moons be (or have been) stable? (Advanced)
- What is the three-body problem? (Advanced)
- General Questions
- What direction do planets rotate? (Beginner)
- Why are stars and planets round? (Beginner)
- Is there really a 10th planet? (Beginner)
- What are the requirements for being a planet? (Beginner)
- Who named the planets and who decides what to name them? (Beginner)
- How can I find my age on another planet? (Beginner)
- Can we colonize other planets? (Beginner)
- Will we discover an 11th planet? What would it be called? (Beginner)
- Do planets radiate noise? (Beginner)
- Who discovered each planet? (Intermediate)
- Why is our solar system so different from all the others we've found? (Intermediate)
- Why do planets rotate? (Intermediate)
- What is the physical difference between a star and a planet? (Intermediate)
- How far is each planet from Earth? (Intermediate)
- Could a planetary system survive if its star merged with another, or if its star went supernova? (Intermediate)
- How can we tell what the interiors of planets are like? (Advanced)
- How do we know what other planets (and stars, galaxies, etc.) are made of? (Intermediate)
- Can planets collide with one another? (Intermediate)
- Orbits
- Have the inner planets cleared their neighborhood? (Intermediate)
- When was the last time all of the planets were aligned? (Beginner)
- How do you measure a planet's mass? (Beginner)
- Why do planets have elliptical orbits? (Beginner)
- Why do the planets orbit the sun? (Beginner)
- Why do all the planets orbit in the same plane? (Intermediate)
- What is the significance of the second focus of elliptical orbits of planets in our Solar System? (Intermediate)
- What is the pattern to the distances between each planet and the sun? (Intermediate)
- What do all the angles in a table for a planet's orbit mean? (Advanced)
- When the Sun converts mass to energy, do the orbits of the planets change? (Advanced)
- Planet Watching
- How do I tell which planet is which? (Beginner)
- What is the observational difference between a star and a planet? (Beginner)
- What was that eclipse I saw in the sky? (Beginner)
- During close approaches, can Mars appear in our sky as large as the Moon? (Beginner)
- Why do planets not twinkle? (Intermediate)
- Why can't we see Venus at night when it is an inner planet? (Intermediate)
- What color is each planet? (Intermediate)
- What kind of eyepieces do I need to look at planets? (Intermediate)
- How did a transit of Venus provide astronomers with the first measurement of the Earth-Sun distance? (Intermediate)
- Why do pictures of distant galaxies have higher resolution than those of nearby planets? (Intermediate)
- Venus
- Comparisons with Earth
- Mars
- How did Mars get so dusty? (Beginner)
- During close approaches, can Mars appear in our sky as large as the Moon? (Beginner)
- Can the sun rise from the west on Mars? (Beginner)
- Is it sensible to consider terraforming Mars? (Beginner)
- Why does one side of Mars look more catastrophic than the other? (Intermediate)
- What are the atmospheres of Mars and Pluto like? (Intermediate)
- If Mars is only about 35-60 million miles away at close approach, why does it take 6-8 months to get there? (Intermediate)
- What was different on Mars in the past to allow liquid water to be present? (Intermediate)
- Is the reddish dust of Mars biogenic? (Intermediate)
- The naming of Mars (Intermediate)
- What color would Mars be if you were standing on it? (Advanced)
- Why does Mars have a dusty atmosphere? (Intermediate)
- Jupiter
- Saturn
- Pluto
- Moons
- Why are there active volcanos on Io? (Intermediate)
- Will astronauts ever be able to go ice-skating on Europa? (Intermediate)
- Can we hear sound on Titan? (Intermediate)
- How do planets capture satellites? (Advanced)
- How can two moons of Saturn share the same orbit? (Intermediate)
- Why do most moons orbit their planets at the equator? (Intermediate)
- Why does Titan, in spite of being smaller than Mars, have an atmosphere more dense than Earth's? (Intermediate)
- Where can I find information on the moons of other planets? (Intermediate)