mindstalk | Entries tagged with astronomy

If you look at e.g. timeanddate, you can see not just sunrise and sunset times, but various twilights. What are they?

On the dusk side -- I expect more of my readers see dusk than dawn -- they are civil, nautical, and astronomical twilights.

Civil: the sun has set[1], but there's still refracted light so it's fairly bright and you won't get mugged.

Nautical: it is darker, and some stars are out, but you can still make out the horizon, making this the *perfect* time for old-fashioned navigation, where you need to see stars and the horizon.

Astronomical: the horizon is gone, and most people would just call this 'night'. But astronomers trying to observe the faintest objects will still complain about natural light pollution.

They're non-symmetric with respect to work: with civil, civilians can still do work, or be coming home from work; for nautical, this is the best/only time that navigators can work; for astronomical, astronomers still *can't* work.

In dusk order, they are CNA, and I don't a better mnemonic than "CNAs really like sunset." (Certified Nursing Assistants.) On the sunrise, side, astronomical obviously comes first, and the sky gets marginally too light for astronomers.

In a fantasy setting, one might imagine various vampire twilights, depending on how robust your vampires are. From "the sun has set, but there is still time to scurry home safely" to "the sun has not yet set but the vampires are already out."

[1] Technical details: sunset means the entire sun has set, i.e. that the upper edge of the sun has passed below the horizon. But the twilights are defined by how many degrees the *center* of the sun is below the horizon: 6, 12, or 18. The sun itself seems to be half a degree wide.

Phobos, the lower moon of Mars, has an orbital period under 8 hours, so from the surface it looks much like a artificial satellite of Earth: over the course of a night it rises in the west, sails across the sky, and sets in the east. In fact it does so twice. Nothing in Earth's natural sky is so quick and regular, and I find myself wondering how astronomy and astrology might have been different if we'd had a Phobos. Not very productive wondering, but still. I suppose it might have been a nocturnal timepiece.

The fact that it really obviously moves west to east seems like it might have had some effect, compared to everything else rising in the east. (The Moon moves eastward over the course of the month[1], but that may be less obvious.)

The other moon, Deimos, has a 30 hour period, slower than Mars's day, so it rises in the east. But it should move quite visibly against the stars, and it takes a couple days to set for a Martian observer.

Wondering about all this reminded me of my old wondering whether the local presence of monkeys, an obvious link between humans and animals, had an effect on Eastern religions.

[1] Over the course of a night the moon moves east to west, like the sun and stars. But night to night, the moon at dusk starts over the western horizon as a waxing crescent, moves overhead as a waxing half, and appears over the eastern horizon as a full moon.

Crossposts: https://mindstalk.livejournal.com/568701.html

My coconut oil thermometer continues to 'work'; I observe my kitchen is marginally under 77 F, given solid but very soft oil.

There are non-maple red leaved trees around here. After a bit of research, I guess they are red plum trees. I also learned that there are red maples native to North America, that are not Japanese maples. Thanks evolution, I thought I had something simple.

I discovered what seemed to be a blackberry tree overhanging the garden: very tall tree, shiny heart shaped leaves, dropping lots of thin "blackberries". Mulberries, in fact, with very mild fruit. (I ate some off the ground. Can't reach the branches.)

I saw Saturn! It's not a planet I'm usually aware of seeing, but my night sky app pointed it out. Which is probably how I IDed it the first time I knowingly saw it.

Crossposts: http://mindstalk.livejournal.com/450931.html

Something I've been brooding about recently, especially after re-reading Neptune's Brood. It's rather amazing how much we think we know about the visible universe, just from peeking out at it from our little planet. Astronomers tell us the structure of the Sun, it's lifecycle, that of other rather different stars, explain novae and supernovae... I'm not saying there aren't any mysteries, but if you stop and think about it, the amount of stellar detail is absurd. We barely know that much about Earth, and the rest of our system's planets -- or planemos, planetary mass objects, big enough to force themselves to be a sphere and at least briefly geologically interesting -- are an endless wellspring of surprises, with more to learn every time we peek closer. What we can guess of exoplanets has not changed that.

But it does make sense in a way. Stars be definition are shining light and therefore information at us. (The Earth intercepts 2 kilograms of sunlight every second, for a gratuitous figure.) That very fact constrains them a lot -- they're big balls of hydrogen and helium and contaminants, under great forces of gravity and heat and light pressure and magnetism. If they weren't just so, they wouldn't fuse; if they weren't balanced between gravity and fusion, they wouldn't be stars. Like a high-speed fish or a rocket engine, there's not a lot of leeway. THey're plasma, so fluid, and tending to homogeneity. Finally, there's a lot of them, all shining at us; if we've populated a periodic table of stars types and age categories, it's probably because we've seen multiple examples of each. In short, it's a data-rich and highly constrained field.

I've just started reading the 1999 edition (from the library) of The New Solar System (Beatty et al.), rather younger (and much thicker) than the one I had as a planetary science major in college. It alerted me to one specific way in which stars fall over themselves to tell us about themselves: helioseismology is a thing. How can we track sound waves in the Sun? Not by listening to them, but by simply looking at them: sound waves in the Sun move the photosphere, the light-emitting 'surface', which causes Doppler shifts in the light. Voila! Your telescope is also a seismometer -- a global seismic detector net, even -- and we can apply seismological techniques to infer the structure and composition of the Sun. Heck, we can apparently even do this with other stars, which I don't remember hearing about before.

By contrast, planets are dark and opaque. They're potentially a lot more complicated: much more diverse in chemical composition, able to be gaseious, liquid, or solid, or all three (solid is the big one, allowing really wacky differentiation); able to support actual chemistry. The Himalayas probably causing long-term cooling and eventually the Ice Ages, by scrubbing CO2 out of the air via excessive weathering, *as well as* causing the monsoon cycle, is my favorite "who would have expected that?" example. And finally, there's not that many observable planets: 32 planemos, including all the large moons, Ceres, and recently named Kuiper belt objects; more like 27 within range of telescopes or fly-by craft so far, though New Horizons will add Pluto and Charon. So even if there is a regular pattern to planets, we could easily lack the data to perceive it.

Still, I'm impressed by how *nothing* closely resembles anything else. Moon and Mercury are different, all the gas giants are different, even Ganymede and Callisto are different. There are some similarities and discernable forces, but AFAIK nowhere can we say "yeah, given A, B is no surprise."

***

As for Kant, the book reminded me that he came up with the nebular hypothesis, that the solar system was formed from the collapse of a rotating nebula of gas. That wasn't his only work in physics. WP is more intriguing than informative, but Kant was cited by Lord Kelvin and Thomas Huxley -- not bad!

***

It seems odd to be reading a thick book from 1999, when there's been so much new work (e.g.), but this seems to be the latest edition from these authors, and I don't know what's similarly lay-comprehensive now. Wikipedia would be more up to date, but this has more depth and photos. And some stuff wouldn't go out of date, like history I hadn't appreciated: just how dead study of the planet was before the space program. NASA had trouble finding astronomers to get on board with them, Kuiper being one of the exceptions.

Also amusing to read the Sun description. Paraphrasing: "we think we know how the fusion works, but 2/3 of the neutrinos are missing. So we're either really wrong about the Sun, or about neutrinos. Leaning toward the latter, because helioseismology supports what we infer about the Sun." Ding!

Wow, I've never needed a geology or planetary science tag on LJ before. Astronomy, yes. Lame of me.

Crossposts: http://mindstalk.livejournal.com/413503.html

Today I learned of a Stross story, Bit Rot, set between his robot novels Saturn's Children and Neptune's Brood. I read it, it's cool, if dark.

It also led me to learn about soft gamma repeaters and magnetars, which can have magnetic fields so strong atoms are deformed into a 200:1 aspect ratio. I may have heard of this before, but still, wow.

Further link following brought me to pair-instability supernovas. Stars of mass 130-250 Sols can have gamma rays so energetic they form electron-positron pairs, removing the pressure imparted by the gamma ray and causing a collapse leading to total fusion of the star's contents, and total disassembly. No black hole remains, the star literally blew itself up, like a Type Ia supernova.

In turn I learned you can get nucleosynthesis by gamma ray. Also that there are proton-rich nuclei whose origin is not well-explained. We know the reactions that can produce them, we just don't know where those reactions would take place.

Also, there's a unit called the foe, a unit for 1e44 Joules, or 1e51 ergs. 'The word is an acronym derived from the phrase [ten to the power of] fifty-one ergs.[2] It was coined by Gerald Brown of Stony Brook University in his work with Hans Bethe, because "it came up often enough in our work".' as it does if you study supernovas.

And that reminds me of the later Heechee novels, which had energy-based aliens from the early universe known only as the Foe, as they genocided any species that might interfere with their project of returning the universe into a dense hot plasma, which one might say would involve many foes...

Crossposts: http://mindstalk.livejournal.com/411933.html

So I've been busy here in Bton. SF dinner, Gamer's Guild, anime club, and of course the wedding, which went great and I had fun, and I also got sentimental. And I've seen almost all my friends already, if some not as much as I'd like. But this isn't about those. This is about what may have been the best stargazing night of my life.

There've been other big nights. The Milky Way, meteors, other meteors, Comet Hyakutake and Mercury (same night, I think), the Southern Hemisphere. But I think this is the top night in my life for identifying what I was seeing.

That's a really low bar, mind you, what with having lived in cities most of life with few country trips and none with a star guide in hand. But still.

Came as I was walking 'home' from anime club, in the cold somewhat clear air, down 2nd street, and hitting somewhat dark spots -- not too many street and house lights, and only occasional car headlights to close my eyes against. It started as I looked north and identified Polaris straight off -- I don't even need the Big Dipper in an urban sky, if you know where north is then Polaris is the only thing visible in that part of the sky. Helps to be intimately familiar with the right angle to look at, of course, which was first identified 9 years ago via the Big Dipper. Anyway, having found that, I looked outward for the Big Dipper.

Couldn't see it. Rather baffling; lots of stars, but none of them right. Couldn't see Orion either, which I usually can if I can't see the Dipper. Baffling! Could see what I thought was Jupiter. But no Dipper.

But hey! As of a year ago, I have a smartphone. And as of sometime, I have Orrery on it, a stargazing program. (Also Stellarium, but that nearly kills my eee, never mind a phone.) So I started Orrery and got myself oriented.

Aha! The Dipper was basically buried behind trees and houses to the north, Orion blocked by trees to the east. 'Jupiter' was in fact Jupiter. But then I looked further. W-like thingy NE of Polaris, Cassiopeia? Yep -- I've absorbed *something* over the years. That's about it for what I knew off my head. But I identified a whole lot more. Perseus; star Capella just over some trees, and later an associated peak to its right that's part of Auriga; Andromeda, manifesting as two or three stars in a line; Triangulum; Aries, also manifesting as three simple stars, just above Jupiter; later, part of Cetus below Jupiter; Pegasus (also somewhat familiar), including a star to the right of Schaet and two stars below it, and a line of stars below Markab leading to Enif; Deneb capping Cygnus, and Altair and Vega by themselves. Maybe Cepheus. I don't think Draco. Aldebaran was below unobstructed visibility. As for magnitudes, I think the 4.6 map was more accurate than the 4.4 map or 4.8, but I wouldn't swear to it.

So, yeah. Biggest ID night ever, with just me and a star map program.

Crossposts: http://mindstalk.livejournal.com/299246.html

Alright John, you can envy me now.

Yesterday G and I went up to Las Campanas Observatory. First he showed me the Magellan telescopes, and later I got to see an image being taken, one with a possible Oh My God Particle event, given a cosmic ray track (or artifact) that amazed all the observers. Today I saw the 100 inch ("It's like my 8 inch Celestron, only much bigger") and 40 inch telescopes, and Indian petroglyphs in the region, and heard the rocks that give the mountain its name ("the bells"), iron rich rocks that ring when you strike them against each other. But last night was the light, when he hauled out his aforementioned Celestron up on the mountain and his Nikon Eagleview binoculars and we went stargazing in the Southern Hemisphere. First we saw the thin crescennt of a two day old Moon, and the Mercury/Jupiter/Venus conjunction. Craters on the Moon, Io Europa and Callisto around Jupiter, Jupiter's banding, the phase of Venus -- old hat for some, but new for a city boy like me, where stargazing tends to mean looking at the Big Dipper or Orion, or finding Polaris.

But then Hemispherical stuff. Upside-down Orion, Canopus, then fuzzy patches visible only out of the corner of one's eye -- the Greater then Lesser Magellanic Cloud. But soon they were visible, even obvious, to direct view. And the Milky Way came into view, not as obvious as it was on Catalina for freshman orientation, but still pretty good. The Southern Cross, actually more of a kite. At the end of the evening he pointed out Alpha Centauri coming up over the horizon, pointed to (along with Hadar) by the short limb of the cross.

We saw a satellite; later, while looking at the nebular glow of the Pleiades through the telescope, I think I saw another satellite zip through the field. I caught a meteor, too. He picked out the Crab Nebula in the scope; I with the binoculars found some open star cluster that he recognized but couldn't ID, above the Milky Way in the south. It's got a wavy line of stars in the upper left, and an M of stars in the lower right, with a band of darkness running between.

S has used the term "house farms" for the monoculture development housing tracts in Southern California; G's translation "granjas de casas" for the Chilean equivalent got instant recognition from Chileans.

There's an 'official' map of the Firefly universe:
http://www.fireflyshipworks.com/2008/11/map-of-the-verse/
G mentioned actual support by Joss; there may be a more informative link somewhere. The construction is a close star cluster with lots of hot jovians and thus moons. Fans have imagined the latter but it's the star cluster that helps to expand the habitable range, or range of zones (maybe). And Blue Sun corporation comes from... a blue sun. And all those Asians we never saw might have been on some world we never saw, there's over 200 of the things. Though I still like the B-Ark interpretation (was that me, or James, or someone else?)