{"id":55237,"date":"2024-02-17T08:34:00","date_gmt":"2024-02-17T08:34:00","guid":{"rendered":"http:\/\/48e4644d-b373-40d0-a36c-21cd4fc809e4"},"modified":"2024-02-19T16:32:33","modified_gmt":"2024-02-19T16:32:33","slug":"a-guide-to-lightyears-the-unit-used-by-astronomers-to-measure-vast-distances-in-the-cosmos","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/rss_feed\/a-guide-to-lightyears-the-unit-used-by-astronomers-to-measure-vast-distances-in-the-cosmos\/","title":{"rendered":"A guide to lightyears, the unit used by astronomers to measure vast distances in the cosmos"},"content":{"rendered":"

Using lightyears to measure distance in the Universe and how long it would take to travel one lightyear by foot, car, plane and rocket. <\/p>

By Jenny Winder\n <\/p>

Published: Saturday, 17 February 2024 at 08:34 AM<\/p>

\n\n

The numbers we use in astronomy are, literally, astronomical. It can be hard to get your head around so many zeros.<\/p>

If we were to use kilometres and miles it would be like measuring your commute in millimetres.<\/p>

To try to simplify things, when we discuss objects within our Solar System, we use the Astronomical Unit (AU) to measure distance.<\/p>

One AU is the average distance between the Earth and the Sun or 150 million kilometres (93 million miles). Our Solar System has a diameter of just 1,921 AUs. So far so good.<\/p>

To measure vast distances across space<\/a>, scientists use the Parsec<\/a>, the distance 1AU subtends an angle of 1 arc-second (1\/3600 of a degree) which is 206,265 AUs, or 30.9 trillion km (19.2 trillion miles) and difficult for most of us to comprehend.<\/p>

So the lightyear is the standard measure of distance for anything outside the Solar System.<\/p>

Earth’s distance from the Sun is 1AU, but to describe much larger distances across the cosmos we need much bigger values. This is where the lightyear comes in. Credit: NASA<\/figcaption><\/figure>

A simple definition of lightyear<\/strong><\/h2>

Put simply, a lightyear is the distance light travels in space in a year, 9.46 trillion km (5.88 trillion miles) or 63,241 AU, 0.30 parsecs.<\/p>

Nothing travels faster than light. It travels nearly one million times faster than sound. A lightsecond equals 300,000 km (186,000 miles).<\/p>

A lightminute is about 18 million km ( 11 million miles) and a lighthour is 1.1 billion km.<\/p>

One AU equals 8.3 light minutes and a Parsec equals 3.26 lightyears.<\/p>

\"A
A diagram showing parallax. A and B show how a nearby star appears to move against its background when Earth is at different positions. C is equal to 1 AU. D is a parallax angle of one arcsecond. E is a parsec<\/figcaption><\/figure>

Lightyears and looking back in time<\/strong><\/h2>

The further we look into space, the farther back in time we see.<\/p>

Proxima Centauri<\/a>, the nearest star is 4.25 lightyears away, so the light we see from it today, started its journey four years and three months ago.<\/p>

If Proxima Centauri exploded today it would take 4 years and 3 months before we saw it happen.<\/p>

The radius of the observable Universe and so the farthest we can see into space is 46.6 billion lightyears.<\/p>

\"Galaxy
Galaxy NGC 1097 is 45 million lightyears from Earth, meaning we see it as it existed 45 million years ago. Credit: ESO\/TIMER Survey<\/figcaption><\/figure>

Travelling a lightyear<\/strong><\/h2>

Our crewed spaceships, like Apollo, reach speeds of around 39,400 km\/h (24,500 mph). It would still take around 27 thousand years to travel one lightyear.<\/p>

A plane travelling at 965 km\/h (600 mp\/h) would take 1 million years to travel one lightyear.<\/p>

A car with an average speed of 90 km\/h (56 mph) would take 12 million years, and if you fancied a walk, at 5 km\/h (3 mph) it would take you a whopping 216 million years to travel one lightyear, with no comfort breaks!<\/p>

Earth orbits the Sun<\/a> at 107 thousand km\/h or 67 thousand mph, so it would take 10 thousand years for Earth travel one lightyear.<\/p>

But our Solar system is also travelling through the Galaxy at 720 thousand km\/h (448 thousand mph) which takes just 1,500 years to travel one lightyear.<\/p>

\"A
A car with an average speed of 90 km\/h (56 mph) would take 12 million years to travel a lightyear. Credit: Jeffrey Davis \/ Getty Images<\/figcaption><\/figure>

Travelling at the speed of light<\/strong><\/h2>

Currently, faster-than-light travel seems an unreachable goal, despite movies showing us using wormholes<\/a>, warp drives and spore drives in the future.<\/p>

The closest proposition is to use the energy and momentum of light itself to propel a spacecraft.<\/p>

A city-sized arrangement of synchronised lasers, firing photons to push a small hand-sized spacecraft to 25 per cent the speed of light.<\/p>

That would get us 4.25 light years to Proxima Centauri in under 20 years.<\/p> <\/body><\/html>\n

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