Savor what’s left of summer


Autumnal Equinox arrives at 10:29 pm Monday, 9/22. Since it takes quite a bit of time for water to heat up, it also takes a long time for it to cool so the ocean at the shore is still pretty warm even though the season’s changed and the air temps are cooling perceptibly. Halloween is the next seasonal milestone, the halfway point between fall and winter.

September 15, 2014


[Dave Heller] Time to make your end of summer plans. Joining me at the beach with pail and shovel is Derrick Pitts, chief astronomer at the Franklin Institute. Derrick, the water is surprisingly warm.

[Derrick Pitts] It certainly is, and boy am I glad it is because I couldn’t get down here during the summer very much myself. But now’s my golden time because even though we’re beginning to lose minutes of sunshine during the day — in fact, by now we’ve lost almost an hour of evening sunlight since June 21 — the ocean continues to hold that heat that it gained over the summer for quite a few weeks afterward. So, water’s still warm, and if you have some time you can still enjoy some of that summer spirit if you just dive into the water.

I’m feelin’ pretty good: Water’s still warm, and in a few months, the amount of daylight will start to build again. But a lot’s happening between now and December 21.

Yeah. First of all, there is a lunar eclipse next month — partial one for us. We don’t get to see all of it. And the other thing of course is the great fall holiday, Halloween. Halloween is the cross-quarter day of the season. It’s the halfway point between the first day of fall and the first day of winter, we all know when that is, October 31. And from that point on, we’ll really feel like it’s fall and really feel like we’re heading toward winter.

And a lot longer nights as well.

Indeed, a lot longer nights as well. So it’s a great boon for folks who want to get out a telescope and go take a look at the night sky. We don’t have to wait until 10 p.m. for the sky to be really dark; the sky can be really dark around 6:30 or 7. But of course, the trade off for that is that the air gets a little bit nippier, a little bit colder, so we have to pick our nights carefully.

Any of those winter constellations available yet?

Yes, in fact some of those winter constellations are making their way above the eastern horizon if you stay up late enough. Right now what we see are the late summer constellations over on the western horizon after sunset. The main ones are almost standing on the western horizon by 9 or 10 p.m. in the evening. So if you go up high in the south you find the main constellations of autumn. Pegasus, for example, is a really good one we can identify that way. But then if we look back off to the east, we begin to see those constellations of winter making their way up. Most notably, Taurus is one of those that comes up early with the star cluster known as the Pleiades. That begins the march of the winter constellation making their way into the evening sky.

  • Harvard College Observatory, circa 1899 / Wikipedia

Now let’s consider the nexus of astronomy and history.

How this works is that from 1880 through 1990 the Harvard College Observatory, with a number of other observatories from around the world, were doing surveys of the night sky. Photographic surveys of the night sky using the biggest telescopes that they had available. Well, the surveys being done were being recorded on glass plates. Not film, like you might expect, and certainly not digital, but these glass plates in the Harvard Collection number to a little more than 500,000. Half a million of them! So imagine we have a glass plate negative taken through a telescope of some area of the sky. Now Harvard did repeated surveys of the sky, and the idea was let’s take a snapshot of what the sky looks like now, and then 50, 100 years from now let’s look at it again and see what changes have taken place in either the star appearances themselves, or galaxy motion or star motion. Any of those things so that we can begin to track what activities happen in our sky, in our galaxy, in our universe. So what’s called metadata — the date, the time, the location, the object being observed — was being recorded in a log book. So what’s happening now with the collection is Harvard is digitizing the collection. And that’s pretty easy for the plates — they can simply scan those in a scanner, and they can do as many as 400 a day. But those plates don’t mean anything unless the data from the log book goes with the digitized data from the plate. So Harvard College is looking for volunteers. They want people to come on board with them, become citizen scientists in a way, and transcribe data from the log book into a digital file that then goes with the newly scanned digital image from the glass plate.

I presume you don’t have to travel to Cambridge to take part in this one.

No, you can do this kind of work online. And that’s the really good thing about it, you can do it right from home and from the comfort of your living room, if you’d like. But it’s a really great way meld history with astronomy. And the reason why is because even though these plates are, some more than 100 years old, the data that they contain really is very valuable. In fact, astronomers still mine those plates for data about the state of our galaxy, the state of the universe, 100 years ago.

Fascinating, getting us from 1880 to the present. Though now with the sophistications and computers and telescopes and computer simulation, can we then project what the night sky will look like from this point on?

Well what the data gives us is an opportunity to create models for what could happen going forward, or what kind of phenomenon we might expect to see. Or make a model of how a certain process might affect other stars so we know what to look for in the future or where to look in the future. So the model gives us something to look for in the current day, and then if we can hunt for that, we might be able to use that as a data point to help try to prove some idea or thought or theory.

  • Harvard-Smithsonian Center for Astrophysics DASCH project – Logbook MF #17. Transcribed and reviewed by digital volunteers.

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