Wednesday, September 26, 2018

high on life

Around now you can see four planets across the full evening sky. One of my favorite things to do in this situation, especially when the Milky Way is also visible, is to visualize how I'm spinning through the solar system and the galaxy. Kinda like XKCD's habit, but with movement along with orientation.


Having four planets overhead makes this really easy and vivid. You can literally see the layout of the solar system in front of you (or rather, looking backwards :) And with a little bit of prior knowledge about the relative distance of things, you can un-project the celestial map back into three dimensions.

Excuse the kindergarten-level illustrations, and the fact that these are outdated from the time of Mars opposition two months back, but here's what I mean. First, here's the view just after sunset, facing north, on August 1st, from Australia.* The sun is just below the horizon to the left, and Mars is rising to your right**. It's a day past full moon, so the waning moon will be rising shortly.***  Jupiter is almost directly overhead, Venus is above and to the left, and Saturn is above and to the right.

The planets are moving right to left across the sky, and that tells you the first key element of your movement through the solar system: You're spinning on the Earth's axis in the direction of doing a cartwheel to your right (except tilted north/forward a bit, since you're not on the equator). The earth's axis is directly below your feet by a few thousand miles, and parallel to a the line from about the back of your neck to your sternum.

The second key piece comes from the knowledge that, looking down on the solar system from far above the north pole, the Earth spins counterclockwise and also revolves around the Sun counterclockwise. So, right at sunset you're flying around the sun in the direction of your feet if you lean forward enough to compensate for the fact that you're not on the equator.


Now, project outwards a bit, and imagine yourself standing on the globe of the Earth instead of the flat ground. The visibility line shows the horizon. Since you're looking North, this diagram is zoomed way out in a basically southerly directly, so the south pole is a little above the center of the Earth's disk. It would have been much simpler if I'd done this assuming you were standing on the equator, but that's not very practical is it! That means that the "flying around sun" arrow is actually pointing down and a little bit right and a little bit up out of the paper.


Lastly, imagine the relative distance between the planets that you know about. All planets revolve counterclockwise around the sun just like the Earth, so Venus, up to your left, is flying down between you and the Sun and will soon catch up and pass us, putting it in the morning sky. Mars is at opposition, so we're passing it by currently and it's rising into the evening sky over the months. Jupiter and Saturn, similarly, are MUCH farther away, much farther than I could ever indicate in a scale diagram, so they move through the sky relatively slowly. You should be able to picture something like this:****


You can see all the angles between what you're seeing in the sky are the same as in the previous two diagrams, but knowing the relative distances lets you imagine yourself flying through space, waving as you pass Mars and waiting for Mercury and Venus to catch up.

Accounting for the solar system's movement within the galaxy is left to the reader as an exercise.

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* For the North American view, you'd have to walk forward in this image about 70 degrees around the globe, thereby putting the arc of planets behind you to the south, instead of directly overhead. The east/west movement doesn't matter because wherever you are on an east-west axis when you go outside after sunset in North American is the same place I'll be in Australia after waiting ~8 hours for the Earth to spin me around to same easterly position.

** This is what Mars opposition means (or any other opposition). On July 31st we were exactly between the Sun and Mars, putting Mars closer to us than it's been since 2001, and correspondingly bigger and brighter in the sky than it's been since 2001. Since we're flying around the Sun about twice as fast as Mars is, in the downward direction designated with the red arrow, now Mars is much higher in the sky at the time of sunset.

*** The moon comes up about 50 minutes later each day, so at full moon it rises at the same time the sun sets, thereby putting us directly between the two and able to see the fully illuminated face. The next day, it comes up a little later and the top edge is in shadow.

**** Yes, planets revolve counterclockwise around the Sun, and I've indicated clockwise orbits. That's because this picture is looking up through the solar system from below (at the south pole) instead of from above.

Thursday, September 13, 2018

An Ode To Free Trade

or, Things That I've Received In Thankfully Nontransparent Tiny Packages From Hong Kong Via Ebay (with Free Shipping!)

10 sawtooth frame hooks (+20 screws) $1.90
1 purple breakaway cat collar, $1.89
1 green breakaway cat collar with engraved tag, $5.99
1 dust brush universal vacuum attachment (as seen on TV) $6.83
1 instant hair bun maker donut, $1.58
10 heavy-duty D-ring frame hooks with screws, $6.99
10 CR2016 batteries, $8.99
10 CR2032 batteries, $7.89
1 77mm UV filter for Nikon cameras, $11.19
8 yards cheese cloth, $3.97
1 citrus press squeezer, $2.19
1 thin hard shell for Nexus 5X phone, $1.93
5 telescoping BBQ roasting skewers, $16.35
3 3-in-1 knife-fork-spoons, $5.58
2 braided micro USB cords, $5.90
1 77mm circular polarizing filter for Nikon cameras, $7.03
1 77mm center pinch lens cap, $3.89
3 2A 2-port USB wall chargers, $16.80
1 red leather coin purse wallet, $5.99
3 77mm neutral density filters for Nikon cameras, $15.59
1 100-LED string of solar powered fairy lights, $15.71
3 50-LED strings of solar powered fairy lights, $34.35
1 1080P HDMI Male to VGA Female adapter, $6.99
2 4K HDMI cables, $15.98
500g pharmaceutical-grade sucralose, $149.87
3 oil filters for Suzuki VL250 Intruder, $28.62
1 large motorcycle cover, $16.89
2 braided USB-C cables, $7.90
1 replacement touch screen LCD for Nexus 5X phone, $67.19
1 silicone dish washing sponge, $3.98
1 pull-up bar for doorways, $14.50
1 personalized engraved pet ID tag, $4.90
20 scopolamine motion sickness ear patches, $29.41
1 mini-DP to HDMI adapter, $4.99
1 Swiss Tech Utili-key multi-tool, $1.87
1 replacement backlit keyboard for Lenovo thinkpad, $39.64
1 tempered glass screen protector for Nexus 5X, $1.00
50 meters heat-resistant double-sided tape, $8.87
4 1600mAh batteries plus charger for GoPro 4, $23.99
1 stainless steel mesh sink strainer, $1.69
10 hair bun spiral claws, $2.29
100g sumac, $6.95
1 large tea infuser ball, $6.00
50 N35 neodymium magnets, $4.90
3 A3 black picture frames, $29.97
20 3M Command small poster strips, $12.98
250g andydrous caffeine, $19.07
1 replacement wrist band with metal buckle for Fitbit Flex, $1.67
100 cinnarizine motion sickness tablets, $30.80
1 pair boot laces, $1.80
1 remote shutter release for Nikon cameras, $19.99
8 mandolin strings, $3.99
1 rocket air duster for camera lenses, $4.47
150 packets of Emergen-C, $30.82
2 aluminum bicycle water bottle holders, $2.38
100 colored push pins, $3.16
4 power cable adapters for Lenovo thinkpads, $6.80


~~~~~

Australia is really expensive, compared to the U.S. But with ebay, given a little bit of patience, I can save ludicrous amounts of money (even more than with Amazon Prime, which I do miss for the things that need to be higher quality than you can count on from Chinese Ebay sellers) and skip the hassle of shopping. I have no idea how sellers are making any money on some of these things. That's the magic of the invisible hand.