As we prepare for the next major solar eclipse in North America – mark your calendars for the 8th of April, 2024! – it’s fun to look back at Observatory records from previous eclipses. On May 10th, 1994, nearly 300 people congregated at the Observatory to take in the spectacle of a partial eclipse.
It’s worth noting that getting the full experience of totality requires a perfect combination of timing, location, and decent weather. Not simple.
This particular event was an annular eclipse, in which the moon’s apparent diameter was less than that of the sun, so that there was always a portion of the sun’s disc visible, creating an annulus (ring) when viewed along the path of greatest eclipse. Still amazing.
Summer is progressing quickly, and it won’t be long before it’s toy kit time once more, including this multicolored assortment of silicone poppers! Available in different colors and sizes, over time you learn which ones pop the best.
Marbled performs better than solid colors.
Pink is often the best. A good one can nearly slap the ceiling from bench height.
It’s not just telescopes at the Observatory. We also have a spyglass. What’s the difference?
There are a variety of potential optics for a telescope, using reflectors to reflect and focus light, using refractive lenses to bend and focus light, using mirrors to turn a beam around corners, using these in combination. Each has its pros and cons, and careful optical design and precise manufacturing work to gather lots of light, to provide good resolution and magnification, and to correct for optical aberrations.
And in doing all of that, the image reaching your eye or the camera sensor gets flipped upside down. Also in reverse, if you’ve got a mirror in your optical train. When looking at stars and deep sky objects, that’s not a big deal. “Up” is arbitrary in space. For terrestrial viewing, however, up matters. Seeing that incoming pirate ship upside down is disorienting. So a good spyglass keeps up as up.
1943!
It does so by using a Galilean refractor design, which has a concave lens in the optical assembly to avoid the upside-down flip. The resulting telescope is necessarily longer than a comparable refractor with convex lenses, and thus heavier. That weight tends to limit the possible objective aperture size, and the practical magnification limits are low. Still: very effective for spotting Edward Teach at a distance, or for identifying the four largest moons of Jupiter.
Binoculars, incidentally, manage to keep the world upright thanks to a set of prisms between the objective lenses and the eyepieces. Yet another handy trick in the optical design toolkit.
Sometimes you just have to love the directness of the manufacturers of scientific apparatus and equipment. “Sensitive Research Instrument Corporation” is not, by any standards, snappy. But it is clear about their product line.
An accuracy guarantee of 0.25%, standardized by Louis Miller on 10/29/62. Charmingly hand-written on this label affixed inside the case. (Sadly, no one marked this one with the price.)
Not presented entirely without comment, as it’s hard to contain the urge toward snark. Yes, we know what this is and why it’s useful; yes, we know what they mean by “gender” and how F/F looks the same but changes things. Yes, yes.
At any rate: the cables which once needed this adapter are gone, as is the equipment it carried electronic messages to and from. Now we just have a block of metal and plastic and the opportunity to squint and say, “I’m not sure that’s how that’s supposed to work.”
In 1963, one could purchase a Standard Astro-Dome with a 17′ inside diameter for the low, low price of $14,667. It must have been a worthwhile investment, because we’re still using it 60+ years later with no plans to update or replace it anytime soon.
When you need to keep things cold, you have options, depending on your temperature needs and what’s available. Carnot cycle refrigeration is handy, effective, and reversible when you need to supply heat (think a heat pump or household refrigerator). You can use the thermoelectric effect via a Peltier device, in which electric current through dissimilar materials causes heat energy to flow in one direction. Or you can just huck a bunch of cold stuff at your target and wait for thermal equilibrium.
Cool running water is remarkably effective in this case. Even colder: ice, though a slurry of ice and water is often faster because of the increased convection and heat transfer through the cold liquid. Sometimes that sizable dollop of energy required for phase transition is really handy! Salt/ice/water slurry gets you colder still, and it’s a great way to make ice cream in the backyard.
Colder still: dry ice, or solid carbon dioxide. (We’re now at the point where you really don’t want this stuff to get on your bare skin.) It has some limited cooling potential, as it sublimates directly to gas at atmospheric pressure, and so good contact and heat transfer can be slow. You can get it to liquid form – the correct cold temperature range and high pressure – which is how we make dry ice when we need it. If you need a suitable liquid for extra-cold chilling, you’re probably looking at liquid nitrogen.
At -77°C, it’s very cold. Your chilling rate becomes limited by the Leidenfrost effect – that thing where a layer of insulating gas forms between the hot and cold materials, thermally and spatially separating them. Same thing happens when you dip a wet finger into a vat of molten lead, or the slippery skitter of a water droplet across the surface of griddle heated just right for pancakes. But, still, cold. Very cold. We use it as a backup for a freezer that’s supposed to hang out at -80°C as long as the power’s on. The stuff inside can handle slightly “warmer” temperatures for the time it takes to repair a power outage.
If you need even colder? Really dedicated folks dial it up to 11 and use liquid helium. That’s a whopping -269°C, which sounds intense. Or, if you prefer, about 4 K. It gets used here at the University, just not in Physics. (Astronomers might study it, but at the safe distances used for telescopic observation.)
All of these extra-cold normally-gases need special handling and care, not only for the temperature concerns, but also for what happens when they warm up and expand and displace all of the breathable air around. (Bad.) We all have some sense of the too-much-carbon-dioxide/monoxide symptoms – sluggishness, blue lips, etc. – but those of us not trained as fighter pilots aren’t as readily aware of the distinct symptoms of too much nitrogen, not enough oxygen. If you are one of the lucky few, you get to undergo normobaric hypoxia training, which can lead to roughly 18 seconds earlier awareness of hypoxia, which sounds like an awful lot in a plane that can travel a third of kilometer in that period at Mach 1.
As for the the dangerous effects of breathing a sudden roomful of now-gaseous helium? We assume your final words are hilariously high-pitched.
Among the stacks and stacks of old records and books at the Observatory, we have a substantial text discussing best practices for astrophotography from…
1895. Sweet.
You may read a scanned version online if so inclined. Fun to note that, broadly speaking, the difficulties remain. With every improvement in technology comes an increased ability to explore and a growing expectation of quality, so there’s always opportunity to do better. From page 2:
“In order to appreciate the accuracy with which the mechanical adjustments must be made, and the care with which they must be used, we should recollect that in a telescope of sixteen feet focal length, a second of arc is rather less than .001 of an inch, — a quantity quite invisible to the naked eye. We are required, therefore, to keep a mass of metal weighing several hundred pounds following the star with such accuracy, for perhaps an hour, that it shall not for any length of time shift to one side of the other from its true position by this amount.“
No one expects an antique box of chocolate bars – a Boston-based brand which went out of business in 1981 – to contain those candies anymore. We reuse boxes all the time, and the key factors are size and durability. D-cell battery boxes are in relatively high demand, for example; good size and sturdy. Chocolates boxes, it seems, were once just right for storing lots of glass plates. This was so long ago, though, that the original use has become somewhat obscure. (The glass plates. No one’s confused about the eventual fate of the chocolate bars.) Now the boxes are more intriguing than their contents.
Five cents seems reasonable.
Idle thoughts bubble:
What an interesting array of flavors! Belmont? Mallowfudge? Creole Nut? Presumably Caramallow is a caramel-marshmallow hybrid, whatever that meant in practice.
Why is it Coconut Cream, but all of the others are ordered as Cream Almond or Cream Walnut? (Cream Brazil Nut?)
“Pure = Wholesome” feels appropriately late-19th-century and kind of creepy.
“Rich In Food Value” feels appropriately early-20th-century and definitely creepy. Or possibly written by ChatGPT; still creepy.
