Light-year is the distance light travels in one year. Light zips through interstellar space at 186,000 miles (300,000 kilometers) per second and 5.88 trillion miles (9.46 trillion kilometers) per year.
How far can light travel in one minute? 11,160,000 miles.
It takes 43.2 minutes for sunlight to reach Jupiter, about 484 million miles
away. Light is fast, but the distances are vast. In an hour, light can travel
671 million miles.
Earth is about eight light minutes from
the Sun. A trip at light-speed to the very edge of our solar system – the
farthest reaches of the Oort Cloud, a collection of dormant comets way, way out
there – would take about 1.87 years. Keep going to Proxima Centauri, our
nearest neighboring star, and plan on arriving in 4.25 years at light speed.
When we talk about the enormity of the cosmos, it’s
easy to toss out big numbers – but far more difficult to wrap our minds around
just how large, how far, and how numerous celestial bodies really are.
To get a better sense, for instance, of the true
distances to exoplanets – planets around other stars – we might start with the
theater in which we find them, the Milky Way galaxy
Our galaxy is a gravitationally bound collection of
stars, swirling in a spiral through space. Based on the deepest images obtained
so far, it’s one of about 2 trillion galaxies in the observable universe.
Groups of them are bound into clusters of galaxies, and these into
superclusters; the superclusters are arranged in immense sheets stretching
across the universe, interspersed with dark voids and lending the whole a kind
of spiderweb structure. Our galaxy probably contains 100 to 400 billion stars,
and is about 100,000 light-years across. That sounds huge, and it is, at least
until we start comparing it to other galaxies. Our neighboring Andromeda
galaxy, for example, is some 220,000 light-years wide. Another galaxy, IC 1101,
spans as much as 4 million light-years.
Based on observations by NASA’s Kepler Space
Telescope, we can confidently predict that every star you see in the sky
probably hosts at least one planet. Realistically, we’re most likely talking
about multi-planet systems rather than just single planets. In our galaxy of
hundreds of billions of stars, this pushes the number of planets potentially
into the trillions. Confirmed exoplanet detections (made by Kepler and other
telescopes, both in space and on the ground) now come to more than 4,000 – and
that’s from looking at only tiny slices of our galaxy. Many of these are small,
rocky worlds that might be at the right temperature for liquid water to pool on
their surfaces.
The nearest-known exoplanet is a small, probably rocky
planet orbiting Proxima Centauri – the next star over from Earth. A little more
than four light-years away, or 24 trillion miles. If an airline offered a
flight there by jet, it would take 5 million years. Not much is known about
this world; its close orbit and the periodic flaring of its star lower its
chances of being habitable.
The TRAPPIST-1 system is seven planets, all roughly in
Earth’s size range, orbiting a red dwarf star about 40 light-years away. They
are very likely rocky, with four in the “habitable zone” – the orbital distance
allowing potential liquid water on the surface. And computer modeling shows
some have a good chance of being watery – or icy – worlds. In the next few
years, we might learn whether they have atmospheres or oceans, or even signs of
habitability.
One of the most distant exoplanets known to us in the
Milky Way is Kepler-443b. Traveling at light speed, it would take 3,000 years
to get there. Or 28 billion years, going 60 mph.
Source: NASA
Source: What is a
light-year? – Scents of Science (myfusimotors.com)
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