Resources and Education

Here you’ll find the resources you need to get started observing, photographing, and more — your essential introduction to astronomy. Find out which telescopes are best for starting out, the basics of using a star wheel, and what terms you need to know.

And that’s just to get your started. As you delve into the hobby, you’ll want to start using our interactive observing tools and star charts, and maybe you’ll even try your hand at astrophotography. Whatever you try, good luck and clear skies!

Crescent cradles the 'old moon'

Earthshine, the Moon’s Darker Side

With a subtle beauty all its own, the earthshine we see glowing in the lunar night invites us to consider Earth's many connections to the Moon This week's crescent Moon offers more than two horns to hang your hat on. Take a close look, and you'll see an entire circle of moonlight. Sunlight illuminates...

Closed universe (top), open universe (middle), and flat universe (bottom).
NASA

Is space flat or curved?

Locally, spacetime is curved by the presence of massive objects. The total mass and energy density of the universe also has an effect on the overall curvature of space.

The dark matter concentrations in the galaxy cluster Abell 1689 are tinted blue. Astronomers determined the location of those concentrations from gravitational lensing.
NASA, ESA, and D. Coe (NASA JPL/Caltech and STScI)

What is dark matter?

Dark matter is a mysterious type of matter that doesn't interact with any form of electromagnetic radiation, i.e., light. Although we’ve never detected dark matter directly, a large amount of evidence points to its existence.

Artist's rendering of a supermassive black hole.
NASA/JPL-Caltech

How big is a black hole?

Black holes are singularities: points of infinitely small volume with infinite density. However, the amount of a mass concentrated in a black hole varies, and the mass determines how wide the black hole's sphere of influence is.

Two-dimensional representation of the three-dimensional curvature of spacetime around a massive object.
NASA

Are black holes real? If so, who discovered them?

The concept of a black hole was first contrived in by John Michell 1783. For a long time, many notable scientists, including Albert Einstein, believed black holes were merely theoretical. However, in the last century, astronomers have gathered a good deal of observational evidence for the existence of black holes.

Our expanding universe

What is dark energy?

Cosmologists have invoked the concept of dark energy to explain the accelerated expansion of the universe, but the nature of dark energy remains one of the most pressing questions facing modern cosmology.

Smattering of distant galaxies imaged in the Ultraviolet Coverage of the Hubble Ultra Deep Field Project.
NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI)

Is there a center of the universe?

The universe began as a singularity that started expanding in the Big Bang. But the Big Bang was no regular explosion. Rather, space itself expanded, so there is no center of the entire universe. The observable universe, on the other hand, is a different story.

Smattering of distant galaxies imaged in the Ultraviolet Coverage of the Hubble Ultra Deep Field Project.
NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI)

How many galaxies are there in the universe?

Astronomers determine the number of galaxies in the universe by counting up the number visible in a tiny portion of the sky, and then accounting for all the regions of the observable universe. A 2013 study estimates that there are 225 billion galaxies in the observable universe.

Planck temperature map of universe

What is the age of the universe?

Determining the age of the universe requires a knowledge of the universe's expansion rate, as well as its density and composition. Cosmologists currently set the age of the universe at about 13.77 billion years.

The Big Dipper asterism in the constellation Ursa Major.
Starry Night Software / A.Fazekas

What are constellations?

In 1930, the International Astronomical Union (IAU) divided the sky into 88 constellations. Each constellation is defined by an imaginary boundary on the sky and named after a classical star pattern within those boundaries. So when we say a star is “in” a particular constellation, we mean it lies within the IAU-defined boundaries of...

Chandra X-ray photograph of young supernova remnant Cassiopeia A.
NASA/CXC/MIT/UMass Amherst/M.D.Stage et al.

How long do stars live? How do stars die?

Both the life and death of a star depend on its mass. Generally speaking, the more massive a star, the faster it burns its fuel and the shorter its life. The most massive stars meet their end in a supernova explosion after only a few million years of fusion, while the tiniest stars continue...

Image credit: NASA

What is a star, exactly?

A star is a luminous ball of gas, mostly hydrogen and helium, held together by its own gravity. Nuclear fusion reactions in its core support the star against gravity and produce photons and heat, as well as small amounts of heavier elements. The Sun is the closest star to Earth.

Image credit: Hubble

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.