Interstellar
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| 3I/ATLAS |
I don't know what non-astronomer types think when they read about comets and asteroids in the news. Without a telescope, and without being familiar with the constellations, they can't go out at night and look at it for themselves. They must use their imaginations. If they've never looked at a comet or asteroid firsthand, they have no idea how to imagine them, and they may not have any understanding of what these objects are.
Even the beginners out there who have Go-To telescopes will find it a challenge to find these objects. That's because comets and asteroids do not appear in the object catalogs built into Go-To telescopes. And if the user chooses to incorporate planetarium software to control the telescope via computer, he or she will need to update the comet or asteroid catalog for newly discovered objects.
I routinely hunt down comets and asteroids with my backyard telescope, even the ones that don't make the click-bait news articles. From my years of experience, I know exactly what to expect, in terms of what they will probably look like in my telescope. I try to take pictures of as many comets and asteroids as I can. Each one is unique. I view them like collectibles. I want to collect them all.
So, whenever I read about a new comet or asteroid in the internet news, my first question is, "Will this object be bright enough for me to get an image?" If a sky chart or an ephemeris for the object isn't given in the article, I will search for one and see if it's going to be visible from my location. Sometimes comets are too low in the western (evening) or eastern (morning) sky. I'm not a morning person, so if a comet isn't visible until 6 or 7 AM, I'm likely to pass on it. I shoot from sundown to about 3 AM most nights and then get around five hours of shuteye by 8 or 9 AM and I can still feel like a normal human being. If I stay up till 7 AM, then I'll be sleeping in until the afternoon and feel like a vampire. Moreover, my eastern sky is blocked by Tucson's Santa Catalina Mountain range, with a peak elevation of over 8,000 feet. That blocks 10 to 15 degrees of sky over the horizon. Many times, a comet won't make it above the mountains before the morning sky becomes too bright to see or photograph it.
If you read between the lines of the previous three paragraphs, you know that "what I think of a new comet" boils down to a simple matter of whether or not it's something I can go out and look at with my telescope. I don't particularly care about all the other wild nonsense that the click-bait articles try to hype up. Phrases like, "How to see the green comet..." or "New comet set to light up the skies..." are so overcooked that you can pretty much accept the fact that the complete opposite will be true. Our eyes cannot see the green color of comets, not even by looking at them through the eyepiece of typical-sized backyard telescopes. The green color can be detected only in photographs. As for lighting up the sky, well, a comet that can't be seen without optical aid certainly cannot be described as something that's going to "light up the sky." The sun and moon light up the sky. An aurora may light up the sky. A super bright meteor or bolide can light up the sky (and the ground). Lightning can light up the sky. But if an 8th-magnitude comet is overhead, it does NOT light up the sky! You won't see it at all without a pair of binoculars, and that means you have to know exactly where to look for it. And if you don't know what an 8th magnitude comet looks like in binoculars, you probably won't even notice it in the field of view while you're staring right at it!
People who know very little about astronomy are left to focus on the sideline hype, which usually is not worth paying attention to. For instance, the article might say, "See this rare comet before it disappears!" Does "rareness" really motivate you to want to go out at night and look for something that you otherwise wouldn't even be interested in? No, but seeing the word "rare" in the headline just might trick you into clicking the link to find out what makes this comet more rare than other comets! And you'll have to scroll down through many paragraphs and close half a dozen pop-up ads to find out that it's rare only because, like most of all the other comets you've ever heard about, it comes around just once during your lifetime. Hmmm. You probably could have guessed that without reading the article!
But 3I/ATLAS actually is something special! And it truly is rare! When my friend asked me for my thoughts about it, my answer most likely would be considered "TLDNR."
The fact is that after I heard about 3I/ATLAS earlier this month, I had already taken the trouble to find out if I was going to be able to see it, and I had kinda made up my mind that it was out of reach for my equipment. So even I had to suck it up and read the click-bait material.
The designation of this comet reveals how rare it is. The "I" stands for "interstellar." And the leading digit "3" means that in all the human history of comet observations, this is only the third one that we know came from beyond our solar system. We know that it came from interstellar space because of its high velocity, as well as the straightness of its path. The orbital viewer in JPL's small-body database browser shows a nearly straight line with a slight bend in its path as it passes between earth and Mars and then goes back out into interstellar space.
The first interstellar object, 1I/'Oumuamua, discovered in 2017, did not have a comet-like appearance. Harvard astronomer Avi Loeb speculated that 'Oumuamua could be of artificial origin, perhaps a spacecraft sent by aliens to collect data about our solar system. The news media created a circus around that story! Radio telescopes, however, failed to pick up any signals coming from 'Oumuamua, restoring our sanity and permitting us to accept a more mundane origin.
But 3I/ATLAS triggered Avi Loeb back into action with suggestions that it, too, might be an alien spacecraft. The only problem is that, unlike 1I/'Oumuamua, 3I/ATLAS does indeed look like a comet, as seen in photos taken by the Hubble Space Telescope.
Those HST photos persuaded me to give up on trying to capture 3I/ATLAS from my back yard. I mean, if the object looks that tiny in HST pictures, I might as well forget about trying to get a shot of it with my peashooter. But the text from my friend caused me to take another look into it.
For all of the doubts I had regarding its visibility, when I downloaded an ephemeris from the JPL page, it showed an apparent magnitude of 17.0. I have successfully shot 17th-magnitude asteroids, so maybe it's not out of reach! And lucky for me, the current position of the interstellar comet in Ophiuchus means that I could try for it soon after sundown on the very day when my friend texted me!
I used TheSkyLive.com to show me where to find 3I/ATLAS on the night in question. That website had ample sky charts and DSS images of the field so that I could directly compare them to my pictures. The only snag was that the month of July is when we experience near-daily monsoon thunderstorms. Clear nights in July are a crap shoot. When I set up my scope on the night of July 27th (July 28 UTC), there were some pesky clouds passing through Ophiuchus.
I took a couple of sequences to create stacks of images which would be used to put together a blink of two images (top of page). Each image is a stack of 45 fifteen-second exposures. The fast-moving comet shifted its position slightly in each exposure, creating a short streak in the stack. The streak doesn't represent the true shape of the object. It is merely a "motion blur" of the point of light that showed up on the individual exposures. The second stack of images had more clouds than the first, causing the steak to appear weaker in the second image. You'll need to zoom in to see it best!
If you are a non-astronomer and you wonder what a 17th-magnitude object might look like, well, let's put it this way. The magnitude scale is rather backwards: the lower the number, the brighter the star. Moreover, stars get logarithmically dimmer as you increase the magnitude number. For example, a star of 1st magnitude appears 100 times brighter than a star of 6th magnitude (a difference of 5 magnitudes). And a star of 6th magnitude is 25,000 times brighter than a star of 17th magnitude (a difference of 11 magnitudes)!
The very faintest stars you can expect to see in a dark rural sky are of 6th magnitude. Remember: the faintest stars you can see are those that are just barely detectable above the sky background. You will not easily see 6th magnitude stars in a dark sky. You will struggle to see them. In the suburbs of a large city, you should not expect to see 6th magnitude stars at all, because they will be drowned out by the canopy of sky glow from the city lights. The faintest stars you can see under suburban skies will be around 4th magnitude. Under dark rural skies, you can expect to see stars as faint as 9th magnitude with the aid of binoculars. And if you use a 12-inch aperture telescope, you can see fainter stars down to magnitude 15.0. To reach 16th-magnitude stars, you would need a 22-inch aperture telescope. But, once again, in your 22-inch telescope, 16th-magnitude stars would be the very dimmest stars that you would barely make out above the sky background. Being able to see a 16th magnitude star in a 22-inch telescope doesn't mean that it will be easy! You will struggle to see a 16th magnitude star in a 22-inch telescope, on the clearest and most transparent (atmosphere) of nights, and with the youngest of eyeballs (as we age, our night vision degrades).
My 11-inch telescope struggles to capture 17th magnitude objects in 15-second exposures! So, while I was optimistic to capture a streak of 3I/ATLAS, I was prepared to accept failure, especially given the sky conditions. After stacking the frames, I had to use the Digital Development stretch in MaxIm DL software to see the streaks well enough to create this GIF. I wouldn't call my pictures "impressive," but I am happy that I got any pictures at all of 3I/ATLAS!
I extend many thanks to my friend who texted me out of the blue and got me to reconsider hunting down 3I/ATLAS. This is the very first interstellar object I've ever attempted to take a picture of. But, for the record, I strongly disagree with Avi Loeb. I do not believe that 3I/ATLAS is a spacecraft that was sent by extraterrestrials to gather information about our solar system. I think it's a natural object (asteroid or comet) that happens to be passing through our solar system quite by chance. Just my opinion, for what it's worth.
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