{"id":508,"date":"2018-06-21T18:29:44","date_gmt":"2018-06-21T18:29:44","guid":{"rendered":"http:\/\/jonvoisey.net\/blog\/?p=508"},"modified":"2018-06-21T18:29:44","modified_gmt":"2018-06-21T18:29:44","slug":"data-summer-solstice-solar-altitude","status":"publish","type":"post","link":"https:\/\/jonvoisey.net\/blog\/2018\/06\/data-summer-solstice-solar-altitude\/","title":{"rendered":"Data: Summer Solstice Solar Altitude"},"content":{"rendered":"

Happy Summer Solstice everyone!<\/p>\n

Since one of the things Ptolemy was concerned with was the angle between the ecliptic and celestial equator, I built a solar angle dial<\/a> to help determine this. Given that the measurements needed to be taken on the solstices (or a solstice and equinox), I set up the instrument today to take the measurement.<\/p>\n

\"\"<\/a><\/p>\n

Let’s back up a bit before getting right into it.<\/p>\n

The first step was to ensure that the dial was aligned along the meridian. I’ve discussed before how the north star is useful for doing this, but since this tool doesn’t have a good sighting mechanism without using shadows, that wasn’t going to be my best bet. Plus it was cloudy last night and this isn’t something I want to leave set up terribly long.<\/p>\n

So I used the shadow method<\/a>. This involves setting a stick in the ground and marking the tip of the shadow over a period of time.<\/p>\n

\"\"<\/a><\/p>\n

Here you can see two buttons I left, marking the tip of the shadow at two different times separated by about half an hour. Connecting those two lines should be the east-west line. However, this method is somewhat imprecise since the sun’s path is an arc. Similarly, the path traced will be an arc as well, so depending on exactly where the points are taken, the path can be skewed.<\/p>\n

To illustrate this, I replaced the buttons with chalk marks and drew the lines connecting the initial one to the later ones.<\/p>\n

\"\"<\/a><\/p>\n

As you can see, the lines are very close, but slightly different.<\/p>\n

Regardless, it was close enough for me to get a good baseline. I’d also looked up exactly when the sun should be on the meridian in Stellarium (1:03pm locally) so if the shadows of the pointers didn’t line up, I could twist my post slightly as necessary.<\/p>\n

However, minor tragedy struck. I’d screwed the dial into a wood post, but when hammering the post into the ground, the force cracked the dial.<\/p>\n

\"\"<\/a><\/p>\n

But a little bit of duct tape and it was at least stable enough to use.<\/p>\n

Worse, about 40 minutes before the sun was on the meridian, heavy clouds started rolling in with drizzle.<\/p>\n

\"\"<\/a><\/p>\n

There was nothing to do except hope that they’d pass quickly.<\/p>\n

Fortunately, they did and it was a clear blue sky come 12:50. As the time got closer, there was a bit of wind as well which made keeping the dial vertical more challenging as the dial wanted to catch the wind and tilt slightly. However, by holding it in place, I could fix this as well as ensure that the horizontal was level as well via the plumb.<\/p>\n

\"\"<\/a><\/p>\n

You can see that the shadow of the upper pointer is falling precisely on the lower one as the corners are still in the sunlight. This meant it was aligned.<\/p>\n

So how did the measurement turn out?<\/p>\n

\"\"<\/a><\/p>\n

It read just<\/em> under 75\u00ba.<\/p>\n

Popping back to Stellarium, the true value was 74\u00ba50’39.7″.<\/p>\n

Can’t ask for much better!<\/p>\n","protected":false},"excerpt":{"rendered":"

Happy Summer Solstice everyone! Since one of the things Ptolemy was concerned with was the angle between the ecliptic and celestial equator, I built a solar angle dial to help determine this. Given that the measurements needed to be taken on the solstices (or a solstice and equinox), I set up the instrument today to … <\/p>\n

Continue reading “Data: Summer Solstice Solar Altitude”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[33],"tags":[36,35,14,34,18],"class_list":["post-508","post","type-post","status-publish","format-standard","hentry","category-data","tag-celestial-equator","tag-ecliptic","tag-ptolemy","tag-solstice","tag-sun"],"acf":[],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p9ZpvC-8c","_links":{"self":[{"href":"https:\/\/jonvoisey.net\/blog\/wp-json\/wp\/v2\/posts\/508","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/jonvoisey.net\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/jonvoisey.net\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/jonvoisey.net\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/jonvoisey.net\/blog\/wp-json\/wp\/v2\/comments?post=508"}],"version-history":[{"count":1,"href":"https:\/\/jonvoisey.net\/blog\/wp-json\/wp\/v2\/posts\/508\/revisions"}],"predecessor-version":[{"id":518,"href":"https:\/\/jonvoisey.net\/blog\/wp-json\/wp\/v2\/posts\/508\/revisions\/518"}],"wp:attachment":[{"href":"https:\/\/jonvoisey.net\/blog\/wp-json\/wp\/v2\/media?parent=508"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/jonvoisey.net\/blog\/wp-json\/wp\/v2\/categories?post=508"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/jonvoisey.net\/blog\/wp-json\/wp\/v2\/tags?post=508"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}