We're on the good side now. Two astronomical events happened this week that give us signs the summer is going away. I know there are some of you in the more northern reaches of the world who respond with the opposite reaction to mine, but we're on the good side of the analemma. I've been saying for years that here in Florida, we're almost completely out of phase with the rest of the US; this time of year, those of you in Minnesota, and most northern places are getting out and enjoying the warmer weather. For me, we're staying inside more. The sun wants to kill us; staying inside under the air conditioning is better. That's the thing about fourth of July barbecues, and I've done my share. I think the best barbecue season is around January through April.
Getting back to the astronomical events, the easy one to document is that yesterday, Thursday (July 6) at 4:06 p.m. Eastern Daylight Time (2006 GMT), the Earth went through aphelion - the farthest distance from the sun that it will be all year. The sun at that moment was 94,506,364 miles from our Earth (measured from center to center), or 3,103,330 miles farther than when the Earth is closest to it (called the perihelion) on Jan. 4.
There are some people who reflexively will be saying, "wait... it's the hottest days of the year. The press is saying it has been the hottest days EVAH, and we're the farthest away from the sun? Shouldn't it be the coolest? Well, no. Bear in mind it's winter in the southern hemisphere now and what makes the biggest difference in the seasonal temperature isn't the distance from the sun, but the 23.5 degree inclination of the Earth's rotational axis to the plane of our orbit. During our summer, the sun is farther north in both hemispheres. It's higher in the sky in the northern hemisphere and lower in the sky for the southern hemisphere. The relative size of the land masses in the northern versus southern hemispheres make our summers hotter and winters cooler, too.
The other event is that, as measured just to the minute, the week of the latest sunset of the year also ended yesterday, July 6. The week of the latest sunset, 8:23 PM here, started on June 29. Yesterday it clicked back to 8:22. The days are getting shorter. Slowly at first, then faster as we approach the equinox in September, but nevertheless, the good trend has started. I'm under no delusions that the weather is going to get nicer tomorrow, next week, or next month. Typically, next month is the roughest month of the year, but we're headed there.
BTW, I can't provide a reference for this because I get the sunrise/sunset times from an app on my phone. The exact time of those two is going to depend on exactly where you are, down to far decimal places in both latitude and longitude. Your days for the start and end of the latest sunsets and their times will vary from mine. From what I see, the app agrees with the numbers my local NWS forecasts provide but I don't know of a site that provides a calendar of the year or the month with sunrise/sunset times on it.
How the inclination of Earth's axis causes the seasons. - By Tauʻolunga - Wikipedia
A short discussion of the Equation of Time and what the analemma is might be in order now that you've talked about aphelion and perihelion.
ReplyDeleteI had to include those equations when I was writing part of the performance model for the space station. About the only factor we igored was the precession of the equinoxes (too slow to matter).
Knowing about the analemma and EoT illuminates why the date the castaways landed on the Mysterious Island was important..
I like this site for sun info: https://www.timeanddate.com/sun/usa/cocoa-beach
ReplyDeleteSurface air temperatures don’t just depend on day length, solar elevation, and distance to the sun. They also depend on the heat storage in the ocean and ground. That’s why the annual temperature extremes lag the solstices in most places.
We've had a cool, wet Summer so far. It hasn't broken 90* here yet, but that's scheduled for next week!
ReplyDeleteMuggy and hot (for New England) here also.
ReplyDeleteAlso on this date:
On July 8, 2011, the orbiter Atlantis was launched on the last space shuttle mission. It is pitiful to think that NASA has essentially just been hitching rides for our manned space program, ever since then.
"A short discussion of the Equation of Time and what the analemma is might be in order now that you've talked about aphelion and perihelion."
I second this thought.
Perhaps strangely, I've never studied the equation of time. Rick T, you're more able to write such a discussion off the cuff than I am. Not that I can't research it.
ReplyDeleteOur June was very unusual weather-wise. It was wetter and cooler than usual for almost the entire month, with an occluded or stalled front wobbling around over the northernmost part of the state from the last week of May almost a full month. Then it broke down and the last week or 10 days has been dry and hotter than usual.
The two tropical storms that started up early ended up behaving more like I expect in an el Nino year. The first (Bret) stayed very far south and was torn apart by wind shear. Cindy curved north while out east of the islands and was likewise torn apart by wind shear. Cindy was more like el Nino-year storms.
I used google and checked the sunset times for the town I'm in, yep the sun is setting earlier now... It's all downhill for the next 6 months...
ReplyDeletehttps://aa.usno.navy.mil/data/RS_OneYear
ReplyDeleteThis is the site I use. It is precise and official such that the data therewith has been used to fend pilots from persec ... I mean prosecution by the FAA.
Mariners may set their chronographs by it.
Bookmarked. While I pretty much never require that much precision, it's good to have such a solid reference.
DeleteThanks!!
I *had* to have such precision, but we got our time hacks from the GPS ground station that was a few hundred meters away from us.
Delete"I went to the source, and asked the horse..."
;P