Light is the window through which astronomers view the cosmos. It fills the Universe. Once light has been emitted, it travels on and on, moving constantly at the speed of light. It only stops when it hits something, be it a gas particle, a planet or even a black hole.
Because of light's eternal nature, we see distant galaxies not as they are now, but as they were when their light was emitted. If it has taken the light from an object a billion years to reach us from a galaxy, then we see that object as it was a billion years ago. Look far enough away, and you could view all the way back to when the first stars began to shine.
Look back even further and it's possible to see light from the very earliest days of our Universe's existence, which we see now as the cosmic microwave background (CMB).
"The simple way to explain the CMB is as the very first light ever emitted in our Universe," says Erminia Calabrese from Cardiff University. "It's been travelling from that moment all the way to today."
In the beginning...
The Big Bang theory states that in the very first moment of the Universe, all the energy and matter of the cosmos was at an infinitely dense point. In the initial fractions of a second of existence, this rapidly expanded, cooling as it went. When the Universe was a second old, it was cool enough for that energy to take on the form of matter particles - such as protons, neutrons and electrons. It also formed light particles known as photons, setting the entire Universe aglow long before the first stars began to shine.
この記事は BBC Sky at Night Magazine の December 2023 版に掲載されています。
7 日間の Magzter GOLD 無料トライアルを開始して、何千もの厳選されたプレミアム ストーリー、9,000 以上の雑誌や新聞にアクセスしてください。
すでに購読者です ? サインイン
この記事は BBC Sky at Night Magazine の December 2023 版に掲載されています。
7 日間の Magzter GOLD 無料トライアルを開始して、何千もの厳選されたプレミアム ストーリー、9,000 以上の雑誌や新聞にアクセスしてください。
すでに購読者です? サインイン
Could We Find Aliens by Looking for Their Solar Panels?- Designed to reflect ultraviolet and infrared, the panels have a unique fingerprint
Researchers searching for life beyond Earth spend a lot of time thinking about what telltale signs might be detectable astronomically. Forms of unambiguous evidence for the presence of life on another world are known as biosignatures. By extension, techno signatures are indicators of activity by intelligent, civilisation-building life.
Antimatter- In our continuing series, Govert Schilling looks at antimatter, the strange counterpart to most of the matter filling our Universe
Particles and corresponding antiparticles are very much alike, except they have opposite electrical charges. For instance, the antiparticle of the electron - known as the positron - has the same tiny mass, but while electrons carry a negative electrical charge, positrons are positively charged.
Where Have All The Milky Way's Early Stars Gone?- Our Galaxy has a curious lack of pristine stars
The Big Bang produced a Universe filled almost exclusively with hydrogen and helium; all other elements - what astronomers call metals - were produced by stars, supernovae and everything that happens later. So if you can pick out a pristine star with no metals polluting it from among the billions in the Milky Way, then you are likely to have a star dating from our Galaxy's earliest days.
Inside The Sky At Night - Two years ago, exoplanet scientist Hannah Wakeford received some of the first data from the JWST
Two years ago, exoplanet scientist Hannah Wakeford received some of the first data from the JWST. In July's Sky at Night, we discovered what she's learned since then.
How to stack DSLR data in Siril
Easily combine multiple frames to boost detailin your astro photos
Lunar occultation of Saturn
You'll need to strike a balance on 21 August to capture the Moon covering the ringed planet
How to plot a variable star light curve
A rewarding project to chart stars that change brightness
Smartphone photography with a telescope
Mary Mcintyre explains how to get impressive night-sky images using your phone
Once-a-century solar storm is overdue
If a Carrington Event struck today it would be catastrophic, says Minna Palmroth
The new era of human spaceflight
There's been a step-change in crewed space missions since the dawn of the 21st century. Ben Evans charts its course and looks ahead to future horizons
