The Alpha Centauri system is not visible from much of the northern hemisphere. The below image shows this star system and other objects near it in the sky. Proxima Centauri, the closest star to our own, is still 40,,,, km away.
Or about , AU. When we talk about the distances to the stars, we no longer use the AU, or Astronomical Unit; commonly, the light year is used.
A light year is the distance light travels in one year - it is equal to 9. Proxima Centauri is slightly closer at 4. The methods astronomers use to measure distances to the stars are pieces of fundamental and active work in astronomy with important implications for how we understand the Universe around us.
One of the most accurate methods astronomers use to measure distances to stars is called parallax. If you hold your finger in front of your face and close one eye and look with the other, then switch eyes, you'll see your finger seem to "shift " with respect to more distant objects behind it. This is because your eyes are separated from each other by a few inches - so each eye sees the finger in front of you from a slightly different angle. The amount your finger seems to shift is called its "parallax".
Astronomers can measure parallax by measuring the position of a nearby star very carefully with respect to more distant stars behind it, then measuring those positions again six months later when the Earth is on the opposite side of its orbit.
One of the obstacles to making this happen appears to have a solution. Image Credit: Breakthrough Institute. It will take thousands of years for humanity's fastest spacecraft to reach even the nearest stars. The Breakthrough Initiatives have been exploring the possibility of reducing this to decades, potentially allowing the scientists who launch the mission to live to see the results.
A new paper, in the Journal of the Optical Society of America B , shows one of the major obstacles for such a project can be overcome with existing technology, although the authors admit other hurdles remain. The more massive an object is, the harder it is to accelerate it, particularly as you approach the speed of light , representing a major problem for any spacecraft carrying its own fuel. Alpha Centauri is the nearest star and planetary system to Earth — it is 4.
Lightweight missions could be given an immensely powerful push and left to voyage on alone. The idea of using lasers to provide this push has been around for decades but is now being explored more seriously as part of Breakthrough Starshot.
The twinkling of the stars reminds us how much the atmosphere affects incoming light. Famed physicist Freeman Dyson calculated that such engines could reach Alpha Centauri within roughly a century, and Carl Sagan suggested that this would be an excellent use for current stockpiles of nuclear weapons.
However, treaties strictly regulating nuclear weapons make these difficult to build. Generation ships accept the fact that a flight to Alpha Centauri might take millennia and so are giant spacecraft that can house generations of astronauts, but much remains unknown about whether people can face the physical and psychological challenges of spaceflights lasting that long.
The most realistic scenario for interstellar travel on the scale of a human lifetime may be the laser sails that Breakthrough Starshot project now proposes. This strategy involves equipping spacecraft with mirrors and relying on powerful lasers to push these probes outward.
Although light does not exert much pressure, prior projects have already successfully tested a number of solar sails — spacecraft propelled by light from the sun. Experimental cosmologist Philip Lubin at the University of California, Santa Barbara, and his colleagues previously calculated that a kilometer-wide laser array orbiting the Earth, firing at to gigawatts, could propel a chip-like spacecraft weighing 1 gram, with a 1-meter-wide sail, to more than 25 percent of the speed of light with about 10 minutes of lasing, which means the craft could reach Mars in 30 minutes, and Alpha Centauri in about 20 years.
Instead of an orbital laser platform, Breakthrough Starshot proposes building a ground-based high-altitude laser array. Breakthrough Starshot would next launch a mothership carrying thousands of space-chips into orbit, and its laser array would then send these probes where no one has gone before.
This strategy does have one significant drawback — the spacecraft currently have no way of slowing down once they reach their target. Still, Lubin, a Breakthrough Starshot team member, suggests these probes could at least fly by Alpha Centauri, relaying data back on what our closest neighbor is like.
Future research could develop even more exotic forms of sails. For instance, Landis has proposed magnetic sails — while laser sails depend on laser beams that disperse over space and so would not push laser sails as effectively at great distances, magnetic sails would get driven by particle beams that could in theory push a spacecraft with relatively constant force over time.
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