re: James Webb space telescope reaches final destination 1 million miles from earth

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Why did it have to orbit around the sun

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Because the earth orbits around the sun and it’s at a Lagrange point which is a gravitationally stable spot. Think of it as just tracking the Earths orbit instead of it orbiting the Sun (although that’s what it’s doing).

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Asking the brains of the OT, how does it see backwards in time?

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We see a thing because light from the thing is observed. For example, you see your monitor because light from the monitor is observed by your eyes. Your monitor is close so the light from the monitor reaches your eyes almost instantaneously.

A "light year" is the distance light travels in one year. It's about 6 trillion miles.

Proxima Centauri (a star) is about 4 1/4 light years away from Earth. That's about 25 trillion miles. When you see Proxima Centauri, you are seeing light that came from Proxima Centauri. That light travelled about 25 trillion miles from Proxima Centauri to your eye. It took that light about 4 1/4 years to travel from Proxima Centauri to your eye. A proton that leaves Proxima Centauri today will not arrive at your eye until about 4 1/4 years in the future.

The Proxima Centauri light you are seeing today departed from Proxima Centauri about 4 1/4 years ago. If you saw Proxima Centauri explode in a supernova today, the light by which you observed that supernova would have departed from Proxima Centauri about 4 1/4 years ago. In other words, Proxima Centauri would have exploded around October 2017, but people on Earth would have seen it for the first time in January 2022.

Accordingly, you are seeing a supernova that occurred 4 1/4 years ago. You are seeing backward in time.

The farther from Earth an object is, the longer it takes for light from it to be observed on Earth. Light from a Virgo star that is one million light years from earth takes one million years to travel to Earth.

Accordingly, if you observed a Virgo star pulsing today, those pulses actually occurred one million years ago, and the light from those pulses took one million years to travel from the Virgo star to Earth for you to observe it. You are seeing pulses that occurred one million years ago. You are seeing backward in time.

Again, the farther from Earth an object is, the longer it takes for light from it to be observed on Earth, and the further back in time you are seeing. You are seeing backward in time.

If one could see far enough, it is possible to see back in time to the beginning of the Universe.

This is a cool post for the math nerds out there:

Twitter

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Around 2 p.m. ET today, JWST will enter the L2 halo orbit, with a 4m 58s MCC-2 thruster burn using 2.3 kg fuel, dV = 1.5 m/s.
Here is my guess of JWST's trajectory before and after the burn.



JWST is in an elliptical orbit around earth, nearing it farthest point and has slowed down to 0.2020 km/s. JWST is high above the ecliptic plane to the right as seen from earth. The MCC-2 burn will steer it a bit towards the L2 point on its way down and back as shown above.
2/
Note that the halo orbit is ellipse-like, 1.6mil km wide and 0.8mil km tall, tilted so that the bottom is closer to earth. The center of the ellipse lies above the ecliptic and closer to earth than L2.
The above trajectory is based on this diagram at jwst-docs.stsci.edu/



Please feel free to point out any mistakes or inaccuracies in the above analysis. It is simplistic no doubt.

It is possible that the words "above" and "below" in the first diagram should be interchanged, i.e., JWST is below the ecliptic plane at this point. The diagram from the jwst.stsci site may be illustrative and not the actual JWST orbit.

Here is the L2 halo orbit of the Herschel Space Observatory. Very similar to JWST. The spacecraft traveled up and right from earth and then maneuvered down and left into the halo orbit, very similar to tweet 1.
Size = 1500k x 800k km, period = 178 days.

herschel.esac.esa.int



The Herschel Space Observatory was retired in 2013, when it ran out of its liquid Helium coolant. Herschel was moved out of L2 into a heliocentric orbit where it would not encounter Earth for several 100 years.

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but it's funny.



Seriously, without him we wouldn't have this photo:

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I was like damn, imagine being the dude who has to say "well I mean i didn't WALK on the moon but i was there"

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Looking at this picture, you can tell who got to walk on the moon and who didn't



Sorry @BCK

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Said he had his best pictures on that camera and it's a shame it floated out of the cabin.

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I feel sorry for all the moms having to wash y'all's jizz out of your pants.

At least take them up to the laundry room instead of piled in the corner of the basement.