If you have ever done public awareness activities about astronomy, given public lectures, volunteered at stargazing events, or written about the sky. anything–And at one point we had to warn people not to look directly at the sun.
The need for such warnings naturally peaks around solar eclipses, when people tend to be discouraged from observing the sun. Raw, unfiltered sunlight is so strong that it can actually create tiny holes in your retina. This is a good reason not to look directly at the sun. Although this generally does not cause complete and permanent blindness, it is not always recommended by ophthalmologists, as it can result in pockmarked blind spots at the back of the eye.
So you can imagine how much that damage is multiplied if you use optical aids like binoculars or even real lenses. telescope. The point of these devices is to collect more light from the sky, like a bucket collecting rainwater, to make faint objects appear brighter.
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literally the sun the brightest object in the sky, Even a small boost from binoculars or a telescope can turn this bright object into a torch. This is the same principle as using a magnifying lens or mirror to start a fire. Never look at the Sun using astronomical equipment unless you want to know what it feels like to stare into the barrel of an active phaser bank. (The only exception is if the instruments are properly filtered.) Also, the amplified brightness is not only harmful to the eyes, but can also have a devastating effect on the telescope’s delicate sensors and instruments. Remember, it’s possible.
So, without further ado, let’s talk about the time when astronomers used the Hubble Space Telescope to observe the Sun. Yes, seriously.
I first heard this story from my friend Glenn Schneider. He was an operations astronomer at the Space Telescope Science Institute (Hubble’s science operations center) after Hubble launched, tasked with understanding and using the telescope’s first flagship instrument called Widefield. planetary camera. WF/PC (pronounced “whiff-pick”), as it is known to those in the know, was launched with an observatory in the early 1990s and remained operational until 1993, when it was replaced by WFPC2.
I worked with Schneider on the development of the Space Telescope Imaging Spectrograph (STIS), a camera that flew to Hubble on the Space Shuttle. discovery It was founded in 1997 and is still in operation. One day, he was using STIS to observe nearby stars and asked me to help him analyze the images because he suspected there were planets there. I don’t remember now what prompted him to tell me that story, but I do remember the mischievous glee on his face when I told him frankly that Hubble had observed the Sun.
When he did that, about 30 horn alarms went off in my head. A thought came to the fore and I was able to say: I have only detoured once to see Venus. Still, observation was difficult and dangerous! ”
He smiled again and told me the rest of the story.
In the late 1980s, when WF/PC was being built, engineers had a problem. Digital detectors used in cameras have been plagued by a problem called quantum efficiency hysteresis (QEH). When WF/PC took images of bright objects, it left behind an afterimage that ruined later observations. Essentially, something bright (not the sun, but Never the sun, Remember? ).
QEH’s treatment was to expose the camera to ultraviolet light, “resetting” the detector and flashing it. QEH was integrated into the detector and only required one modification before WF/PC was replaced by WFPC2. Given that the Sun emits ultraviolet light all the time, Schneider and his colleagues decided to take advantage of it once Hubble was in orbit.
But how did they get all these purifying photons into the detector? Here’s the trick, Schneider told me: Engineers didn’t actually point Hubble at the Sun. That would be bad. Something like, “Let’s destroy much of the valuable multi-billion dollar observatory equipment.” Instead, they realized they could turn the telescope with its back to the sun and point it directly at the sun. away From our star in a placeholder spot in the sky called Anti-Sun, It is a point that moves in the sky due to the orbital motion of the Earth and Hubble, but it is always 180 degrees opposite the star.
Next, a small “pickoff” reflector (a bit like a submarine’s periscope or a dentist’s mirror) is deployed outside the instrument bay on the side of the back half of the Hubble to capture sunlight and direct the WF/PC’s camera. I was able to turn to
So they built the necessary equipment, launched Hubble into orbit in April 1990, and executed their ingenious plan in December of the same year. Hubble’s backside was warmed by the Sun, its pickoff mirror popped out, and WF/PC received a cleaning blast of ultraviolet light from 150 million kilometers away to clean QEH’s detector.
Because the Sun is much larger than WF/PC’s field of view, engineers programmed Hubble to make a series of very small movements that scanned the entire Sun, taking a series of split-second exposures to I drew a map of our planet. The WF/PC, on the other hand, was equipped with a filter that blocks visible light and only allows some of the “far” UV radiation to pass through, ensuring that the correct amount of sunlight hits the sensor. Hubble’s ability to stare at the Sun not only made the QEH scrub possible, it also allowed engineers and scientists to see exactly how light reflected inside the telescope. This is useful both for pointing telescopes and for analyzing future scientific images.
The images engineers ultimately obtained were full of defects and artifacts. With a light source this bright, any camera will reveal many sins. Some of the scans didn’t even show the Sun, but overall they scanned enough to create a rather garish image of our star. It was the first solar image ever taken in the deep ultraviolet and predates NASA’s space-only solar observatories, such as the Sun-Heliophysical Observatory.
Even now, when I tell people about solar eclipses and sunspot observations, I caution them never to do so. Until now Looking at the sun without proper protection or filters sometimes puts a wry smile on your face. Because I know that the super-cautious, risk-averse engineers at NASA used one of the most expensive observatories ever built to observe the brightest and brightest sun. It’s a dangerous light source in the sky and basically cleans your camera.
It turns out that sunlight really is the best disinfectant.
