Childrens Illustrated Encyclopedia

Astronomy

48

Exploring thE univErsE

stars and other objects in the universe produce streams

of tiny particles and many kinds of waves such as radio

waves. Except for light, these waves and particles are all

invisible, but astronomers can study them to provide

information about the universe. the atmosphere

blocks many of the rays, so detectors are

mounted on satellites that orbit

above Earth’s atmosphere.

x-rays

special satellites carry detectors

that pick up x-rays. these

satellites have discovered black

holes, which give out x-rays as

they suck in gases from

nearby stars. this is an x-ray

image of a nebula blown off a

star that exploded.

infrarEd rays

objects in space can also send

out infrared (heat) rays.

satellites and ground-

based telescopes pick up

these rays. they can reveal

the centers of galaxies

and gas clouds called

nebulae (right), where

stars are forming.

ultraviolEt rays

stars that are much hotter than our sun give

out far more ultraviolet radiation than visible

light. this ultraviolet image of a spiral galaxy

was taken from a space observatory to help

astronomers understand when and

where new stars have formed.

gamma rays

some satellites detect gamma rays, which are

waves of very high energy. gamma rays come

from many objects, including pulsars, which

are the remains of exploded stars. this is

a gamma ray map of our own galaxy.

visiblE light

telescopes on the

ground and on satellites

detect the light rays

that come from planets,

comets, stars, and

galaxies. Earth’s

atmosphere distorts

light rays, making

pictures slightly

fuzzy. however, new

computer-controlled

telescopes are able to

reduce this distortion.

An image of a

nebula made with

an optical telescope.

Radio image of a

quasar. A quasar

is a kind of

powerful

galaxy with a

very bright

center.

radar signals

astronomers

produce radar

maps of planets

and moons by

bouncing radio

waves off their

surfaces. the

radar map of

venus (left) was

recorded by the

Pioneer Venus spacecraft

of the united states.

the map is color-

coded to represent

plains and mountains

on the planet’s surface.

Some neutrino

detectors consist

of large tanks of

water, in which flashes

of light occur as the

neutrinos pass through.

An array of sensitive light

detectors pick up flashes of

light produced when neutrinos

enter the tank.

nEutrinos

tiny particles called neutrinos

come from stars. most neutrinos

pass right through Earth, but

special detectors lying deep

underground can detect a few

of them. by studying neutrinos,

astronomers can find out about

the sun and exploding stars.

radio wavEs

many bodies

produce their own

radio waves, which are

picked up by the large

dishes of radio telescopes.

objects called pulsars,

quasars, and radio

galaxies were

discovered in this way.

Find out more

black holes

moon

planets

satellites

space flight

stars

sun

telescopes

universe

The ancient observatory at

Jaipur, India, contains stone

structures that astronomers built

to measure the positions of the

sun, moon, planets, and stars.

Sky watcherS of the paSt

in the third century bce, the greek scientist aristarchus

suggested that Earth and the planets move around the

sun. the telescope, first used to observe the heavens

by italian scientist galileo, proved this to be true and led

to many other discoveries. in the 1920s, the astronomer

Edwin hubble found

that stars exist in huge

groups called galaxies

and evidence that the

universe is expanding.

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