Wednesday, July 25, 2012

Wishing on stars.... with accurate science

There's a meme which keeps going round Twitter (and this morning appeared in my Facebook) stream which says:


We apart from being depressing, it's not actually true. And I am finally decided today to write why not.

All of the stars we see in our night sky are part of our own Galaxy - the Milky Way.

This is how the night sky looks from a really dark site (in a beautiful image taken by Stephane Vetter which appears on APOD). We live inside our galaxy, so we see stars in it in all directions, and along the disc of the galaxy (which is shaped a bit like two fried eggs held back to back) we see lots of stars all close together on the sky.



This is a picture of a nearby galaxy - the Andromeda galaxy, which has a similar structure to what we think the Milky Way would look like from the outside (also from APOD)


Andromeda Galaxy: Credit & Copyright: Jason Ware

We can measure distances to stars and other structures in our galaxy, so we know to a good level of confidence that it's about 100-200 thousand light years across. So every star we see in the night sky is closer than 200 thousand light years away. That means the light from them travelled for 200 thousand years or less to reach your eye.

 In fact most bright stars in the night sky are much closer than that. Most of the stars we see in the sky are within a 1000 light years (e.g. this list of the brightest 26 stars in the night sky), so the light from them has taken less than a 1000 years to reach your eye.

So if the star you wish on is a bright one in the sky (at a guess I'm going to say it is), that means it's probably within 1000 light years from us. So the light from it has been travelling for 1000 years to reach your eye. That's a long time, but it's not a million years, and it means that it's unlikely that that star is already dead.

 Most stars live for billions of years - only the very biggest live for shorter - but even that is a million years.

 The things which are millions of light years away, and in which the stars likely are already dead are all the other galaxies in the Universe. However the most distant one you can see with your own eye is the Andromeda galaxy (check out that faint blob below the Milky Way to the right of the all sky picture above - that's Andromeda; or see me point it out in this video). Andromeda is far away - about 2.5 million light years away, but even at that distance most of the stars you see whose light has taken 2.5 million years to reach your eye will still be alive.

Basically what I hope I've convinced you is that unless you're dreaming on stars in galaxies so faint you can't see them with your own eye, the statement above just isn't true.

So keep dreaming. That star most likely isn't dead already, and your dreams don't need to be either. After all I got to become a professional astronomer and have two beautiful kids as well.

27 comments:

  1. Valuable information in your blog and I really appreciate your work and keep it up dude I really very informative blog about the Science learning class well done.
    Science learning class

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  19. (2b)...interstellar travel (thousands G of constant acceleration)... electromagnetic force creating artificial gravitational force: "electrogravitics" effect, electric currents very high voltage using Tesla/Brown electromagnets and capacitors...gravitational transformers... They say that secret Tesla coils are so powerful that bend the same Gravity and the Ships and crews do not feel sudden accelerations or directional trajectory changes. So perhaps instead of antimatter rockets, in the future Spacecrafts will use Tesla anti-electromagnetic field impulse...

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  20. ...interstellar travel not acceleration constant (graphene: planet errant)... every bit a Terraformed planet errant into a bubble graphene how diamond transparent...with fusion reactors which will give the light and heat how an artificial sun, encircling an antigravitational field Tesla/Brown "electrogravitics" prevents objects collision against the "blue-arch of heaven"... Who needs already a star...

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  21. Interstellar travel /without religion/,,, religious-miserable intentionally maintain years and years forever? that "Third World" because WITHOUT POOR AND IGNORANT THERE IS NOT RELIGION,,, the religious are the firsts that not belief in "God", thus the Inquisition (miserable-religious did make burn alive in the "bon-fire" to Human Beings in the Middle Ages,,,"bon" from French bon: "good",,,), thus miserable-religious-criminals Vatica abuse of the poor Innocents, thus miserable-religious mislead to the foolish, thus miserable-religious bribe to the folks. At present miserable-religious-terrorist-religious from other credos are burning the forest in the entire World obviously using tech-artefacts (drones, balloons,,,for that reason, news, are robbing drones to the shops: governments must put in the forest towers of radar and nocturnal infrared for early detection of those drones used by terrorist-religious, although is more cheap and easy to say the truth and to declare that the RELIGIOUS ARE ENEMIES OF THE HUMANKIND), and the miserable-religious occult-power Rome-saint (terror against reason how they did to Galileo Galilei,,,recent threat: "the III World War has already begun") protects to other credos and silences to Politicians and the Global Media (they never say that are the incendiary-religious) for that the innocent people that still say "oh my God" do not know it a fact already evident: IS TRUTH THAT RELIGION IS LIE

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  22. ...electric cars (charge in street-lamps)... every street-lamp of the World with e.g. 4 standard electric-plugs 220 v.ac. Each electric car exits from factory obligatorily with 2 electric-plugs for 220 v.ac, one of entrance and other of exit. ENTRANCE PLUG: the own car´s converter adapts the network-current to the adequate voltage of the car. EXIT-PLUG: free available for whichever car that arrives and cans connect to the car before. So nobody has that wait for, all cars that arrive to street-lamp they can connect in line one another. When a car finishes its charge, disconnects all and runaway, the others go advancing towards the street-lamp and connect again one another. So nobody has that wait for. How the GRAPHENE BATTERIES Have Not Memory Effect, they can disconnect/connect without problem. If government has that give money for that electric-charge to each one, can do it applying a money-charge by kms/year declared. Electric car´s charge solved the problem. Have to put already the plugs in all street-lamps around the World...and the factories must to put those 2 electric-plugs to all cars, finished the electric-charge´s actual problem, for electric cars.

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  23. TO THE NEXT WAR OF THE GULF THAT GO THE GULFS OF THE WARS

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  24. ...interstellar travel not acceleration constant (laser)... L=2*3.14*r... that beam of a laser pointer that turn 180º, from horizon to horizon, in 1 second and 4 imaginary semicircular screens located, for example, to the distances from Earth... 1: 95493 kms... 2: Moon (384403 kms)... 3: Sun (150 Million kms, 1.5*10^8)... 4: Andromeda (2 million light years...19 Trillion kms, 1.9*10^19), Universal Large Scale: 1 billion=1 million of millions, 10¹²)... The mark of laser pointer to reach, would move alongside each screen to an angular speed of 180º/sec and a linear speed, based on the light, of...(3.14*r)/c... km 95493=1c... Moon=4c... Sun=1570c... Andromeda galaxy= 198 Billion*c, (1.98*10^14)*c... If turn laser pointer to the right, why is going to bend each laser beam to the left, not to exceed c, from km 95493, radius "frontier" in which the speed of laser mark on the screen = c ?... Decreasing magnitudes have a close limit, but growing...have an "infinite" limit, to our knowledge, understood here as "infinite", at least, an exorbitant figure... as with the TEMPERATURE (-273 ºC → "infinite")... MATTER (quark → "infinite")... TIME (0 → "infinite")... SPACE (0 → "infinite")... why it would be SPEED different?...(0 kms/sec → "infinite")...

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  25. (2)...interstellar travel not acceleration constant (laser)... the question is to ask oneself whether we should consider as a real or fictitious speed the apparent displacement of laser mark on the screen. Because (apart from the different photon´s wave trains that make up the light beam are "almost" parallels, that is divergent, increasing the cross-sectional area of light beam with distance, and becoming thus increasingly tenuous) it´s really not the same light beam that rotates, but an "unlimited" number of light rays with limited length, leaving together from light source but, on turning this, grow apart laterally from each other, as the ribs of a fan, with increasing travel distance; as we see in harbor lighthouse that rotates and the look towards us, seeing 1 beam of light instantly. So, as go turning laser pointer, each laser beam that go out in its direction going straight and to reach screen leaves its mark a moment, the next beam leaves its mark a moment, etc...separate two adjacent marks for a dark space, bigger in each farther semicircular screen, proportional to the radius. What we would see, as in frame of a movie, how the continuous displacement of 1 single mark apparent... Of course at an Andromeda´s radius, without obstacles, the photons of each waves train would arrive...but the others photon´s wave trains of laser beam would be so far...that would not see the mark.

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  26. (2b)...interstellar travel not acceleration constant (laser)... But, if someday could make a laser-ray with its photon´s wave trains auto-correcting the divergence...how if they go away inside of a fiber-optic tube reflecting on the walls without can go out, although the ray would travel millions of light-years, to the end would arrive the beam cross-section with the same area that beam departed from the light source... Laser/Antilaser? Trajectories: photons divergent, perhaps antiphotons convergent?, then would go 2 concenter "tubes of light" ◙, normal photons interior-tube divergent/antiphotons exterior-tube convergent, perhaps repulsion photon/antiphoton...the exterior-antilaser prevents go out outside the interior-laser; and the interior-laser prevents go in inside the exterior-antilaser...maintaining always the same diameter... What would happen to arrive those intact laser marks to the distant semicircular screens?...hyperluminal-speed.

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