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Library of Past Questions

We realize that, if you don't know the keywords that we use for the topic areas, it would be difficult for you to select the right area for submitting your question. So here we describe each topic area using a few sample questions. Our Library Search Engine is another excellent way to find the relevant topic area, and even archived answers for your question!

Topics About Which We Answer Questions

Astronomy as a Profession

  • What is it like being an astronomer?
  • Which institutions offer the best programs in astrophysics?
  • What does it take to work for NASA?

Binary Star Systems

  • What is Cygnus X-1?
  • Why are binary stars interesting?

Black Holes

  • How has it been demonstrated that black holes are real?
  • What evidence is there for a black hole at the center of our Galaxy?
  • What properties define a black hole?
  • What would happen to Earth's orbit if the Sun became a black hole?
  • How do black holes emit X-rays?

Cosmic Rays

  • Why is the study of Cosmic Rays important?
  • Who first discovered anti-matter?


  • What does the evidence tell us about the origin of the Universe and what is the evidence that concludes this point?
  • How do you determine the age of the Universe?
  • How do you measure the size of the Universe?
  • Is there enough matter in the Universe for a "Big Crunch"?
  • Which formed first in the Universe - galaxies or stars?

Dark Matter and Dark Energy

  • Can you tell me how dark matter affects galactic spin?
  • How are WIMPS distributed in a galaxy?


  • Can you tell me about those new planets that were found?

Gamma-ray Bursts

  • Exactly how energetic are Gamma-ray Bursts?
  • Could Gamma-ray burst we are seeing be the effects of the formation of a new black hole?
  • How can two merging Neutron Stars make a Gamma-ray Burst?

Milkyway and Other Galaxies

  • How large is the Milky Way Galaxy?
  • What is the proof that the Milky Way is a barred spiral?
  • What different types of galaxies are there?

Neutron Stars/Pulsars

  • What is the difference between pulsars and neutron stars?
  • How does a Magnetar form?
  • How do you know the approximate weight of a neutron star?

Physics of Stars

  • How are the temperatures of stars related to their colors?
  • How do astronomers find the distances to stars?
  • How does the Sun compare to other stars, is it average?
  • How are stars formed, and how do they end up?

Quasars & Active Galaxies

  • What are Quasars? Is the Earth affected by them?
  • Why don't all Quasars show the nebulosity of host galaxies?
  • What is an AGN (Active Galactic Nucleus)?


  • What evidence is there that supports the theory of curved space?
  • Why is it not possible to travel at the speed of light?
  • If photons have no mass, how are they affected by gravity?
  • How fast do gravity waves travel?

Supernovae and Their Remnants

  • What is the difference between a nova and a supernova?
  • How could an element heavier than iron be created?
  • What caused the ring around SN1987a?

X-ray/Gamma-ray Astronomy

  • How does an X-ray Telescope work?
  • How are X-rays and Gamma-rays produced in space?
  • Do Gamma-rays penetrate our atmosphere?

Topics About Which We No Longer Answer Questions

We no longer answer questions on these topics, to concentrate our limited resources on questions on high energy astrophysics and closely related areas (see this page for more explanation).

Earth and Moon (also calendars)

  • How does the tilt of the Earth's axis affect the seasons?
  • What effect do the tides have on the Earth's rotation rate?
  • How do sunspots affect the Earth?
  • Why is the Moon's revolution and rotation period the same?

General Astronomy & Astrophysics

  • What is interferometry?
  • When a star (or light source) is moving away from you, does it emit blue or red light?
  • Who discovered that the Earth orbits the Sun?

Night Sky (stars, planets & more)

  • Why did the Moon turn red during the last lunar eclipse?
  • What are the three brightest stars in the summer sky?
  • Can you see satellites with the naked eye?

Satellites & Space Technology

  • What's in rocket fuel?
  • What is the altitude required for a geostationary orbit?

The Solar System

  • Does the Sun rotate?
  • Why aren't the orbits of the planets circular?
  • Why are the densest planets closest to the Sun?
  • What is the average thickness of Saturn's rings?
  • What would an alien life be like on Europa?

Space Travel & Exploration

  • What do I have to do to become an astronaut?
  • Who was Valentina Tereshkova?
  • What is the farthest a spacecraft has ever been from Earth?
  • Is a manned trip to Mars and back possible very soon?