As you may know, Google Reader is set to disappear on July 1st. I (finally) transferred my subscriptions. It took longer than i expected, and transferred less than i'd hoped. Reader says you can export your date via Takeout. You get to save your stuff to your local hard disk. I downloaded everything, which gives you a .zip archive. I unzipped the zip (there's an unzip command line in Linux, but it's probably easy on any platform).

Historically, i ran Sage in Firefox as a reader. When Google Reader came around, I switched to it so that I could continue where i left off on multiple machines. With Google Reader gone, i've switched back. The directions found by searching the Internet yielded lots of false leads. What works is to bring up Firefox and Sage, in the options menu (on the left), import OPML, browse to the .xml file in the stuff you downloaded and unzipped. What you get is the subscriptions. It didn't have the stuff that's marked as read/unread, however.

Sage has changed since I last used it. It looks better. But it's still a basically simple blog reader. Since I really mainly use one machine, i think i'm going to like it better than Google Reader. For one, it either seemed impossible, or was impossible to mark something as unread that i might have started but didn't finish, or simply wanted to reread.

Sage shows the articles in the browser, just like they'd appear on the original blog. That's because you're looking at the original blog. Google Reader reformatted stuff. This was OK sometimes, but not always. And though you could click to see it in the original form, you had to do that in order to see if you were missing anything. Why not always look at the original? And, some blogs would make a big deal of how their work was copyrighted, and prohibited derivative work. Google Reader was clearly making a derivative work. And, this could hurt the original blog. That's because Google Reader didn't do any advertising for the original author - though they did do some for themselves.

## Monday, June 17, 2013

## Friday, June 14, 2013

### How far can the Sun be seen?

How far away from the Sun can you just barely see the Sun (using Wikipedia)? The Sun is magnitude -26.74 (from Wikipedia). The dimmest stars one can see with the naked eye are approximately magnitude 6. The Sun would have to be |-26.74 - (6)| = 32.76 magnitudes dimmer. The formula for magnitudes is x^5 = 100, x = 100^(1/5), where x is the multiplier to get from one magnitude to the next. The factor dimmer that Sun must be is x^32.76=12,705,741,052,085 (more or less). Light gets dimmer with the square of the distance. Since the Sun is at one AU (x^32.76)^(1/2)=3,564,511 AU is the distance where you can just barely see the Sun. How far is that? 1 AU = 149,597,870,700 meters, exactly. 3,564,511 AU * 149,597,870,700 m/AU = 533,243,305,691,677,319 meters. 1 light-year = 9460730472580800 metres (exactly). 533,243,305,691,677,319 m / 9.4607×10^15 m/LY = 56.363861885414590497131460401964 light years. (OK, so that's more digits than we need). If you were 56.364 Light Years away, you'd be just barely able to see the Sun.

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