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[Asherah]

Leonids Meteor Shower
November 15-20

The Leonids Meteor Shower is one of the two largest meteor showers of the year. It occurs each November when the earth passes through the tail of the Tempel-Tuttle comet. The name Leonids derives from the fact that the shower appears to emenate from the constellation Leo. This is, of course, an illusion, as the "constellations" (which are themselves an illusion) are very far distant from the tail of the comet.

Although the "stars" may appear to "fall" at a rate of several thousand a minute (as was the case in November 1966), generally it's more in the range of 10-15 an hour. They tend to be long white streaks that have a gentle arc to them.

The best time to observe the Leonids is between midnight and around five a.m., when the skies begin to lighten. The nightly peak is generally between 2 and 4 in the morning, since Leo rises at about 1:30 a.m. this week. The peak of the shower itself should be the night of the 16-17th.


For people who want to stay up late and watch the meteor shower, the light from the full moon will cause significant interference. Early birds, however, may be treated to better conditions, since by 4 a.m. the moon will be only a few degrees above the western horizon.  At that point, Leo will be about 50 degrees declination. Declination is the degree angle measured from the horizon. The horizon is 0 degrees and the zenith (the point directly overhead) is 90 degrees. (At 4 a.m. the very bright "star" at the zenith will be the planet Jupiter, currently "in" the constellation Gemini.)

Keep a watch on the extended forecast (Americans can check out http://www.weather.gov/), and plan to meteor watch on a night when it's going to be as clear as possible. Bundle up, make a nice picnic (yummy hot snacks), fill your thermos with hot cocoa and marshmallows (or tea or coffee), grab as many friends as you can and prepare for an hour or two of lounging in your backyard (preferably under sleeping bags) watching the show. It WILL be cold (in the northern part of the northern hemisphere). If you're in an area with too much light pollution, there are sites online that will show you, relative to your position, where the nearest "dark sky" spots are.

If you can't bring yourself to face the cold and/or you can do time-lapse photography, set it up to take pictures of the eastern sky (it'll be about 100 degrees east). Even in light polluted places and even with the moon glow, you may be able to get some pretty good shots. Be sure to share them with us!

[Asherah]

If conditions are right you MAY be able to see them from a large, very clean east-facing window.

This morning it's completely overcast.

[Diredog]

Declination is measured from the celestial equator (Earth's equator, projected out into space), not from the horizon.  Just for future reference.  While it DOES generally line up pretty well, that's only the case if you live in a level/flat area, such as Florida.

Also, +45 degrees DEC is a little more accurate than +50 degrees DEC.  Since the constellation of Leo is pretty much perpendicular to the Earth Edit: at this point in the year, most of the "body" of the "lion" is between +43 and +47 degrees DEC.  +50 degrees DEC is roughly the base of his "neck".

But otherwise, yes.

You forgot to mention that there's a full moon the next couple of days, so it will obscure a lot of the meteors.  Also, there's two peaks for the showers this year: 5 AM/0500 EST, favoring North America, and 11 AM/1100 EST, favoring the central Pacific.

And, for anyone curious, the reason why this is an annual thing is because the meteors are debris that was picked up by Comet 55p/Tempel-Tuttle, or material that has broken off of the back of the comet.  This comet orbits the Sun in nearly the same amount of time as the Earth, albeit on a different orbital path than us.  This causes the comet to cross our path in the same general time every year.

[Asherah]

ACTUALLY, I did mention the full moon, but only in a couple of words. Fortunately it will be low on the horizon at 4:00 which is when the viewing will be best, and all the NICEST and NEATEST people are already up doing THINGS.

I was always under the impression that you calculated declination from "flat".  You don't worry about the fact that there might be hills in the way. But if you take your sextant (everybody has a sextant, right?) and use 90 degrees as the zenith, you will automatically get 0 as the "horizon", visible or not. I think that derives from sea-faring navigation. Am I thinking of "altitude" for landlubbers?

And that 50 degrees was a darned good guess, wasn't it? I even did it without a sextant and looking at emphemera to estimate. You probably have better resources than I do.

It's heavily partly cloudy now...

[Diredog]

My bad, I was trying to check Leo's position and the peak times, and skipped over the full moon bit on accident.

But anyway, "altitude" is a measure of how high off the ground you are.  What you're thinking of is trying to find longitude and latitude by calculating a triangle.  Declination works like rings on a sphere, not angles from a point; otherwise, it would be with 0 as the horizon.

Motherdang, I just realized I used the wrong projection.  Leo's actually at +15 degrees DEC, not +45.  +45 is on an azimuthal projection, which DOES go off of the horizon and hits 90 at the viewer's zenith, like calculating longitude/latitude, because in that instance you ARE calculating a triangle.

You don't use DEC for that, instead, degrees N/S ("up/down") or E/W ("left/right").  Whereas the PROPER projection would be on an equatorial grid, where the equator is 0 degrees and +90 DEC is where the rotational axis of the Earth points.  In that instance, you use +/- DEC for "up and down," and 0 to 23:59 hr right ascension for "left and right".

[Asherah]

ATTITUDE not altitude! But that's not the right term either...

And you're right, I was thinking AP not DEC and still probably getting it wrong. AND by the way, this is precisely why I asked YOU, Mr. Chief Astronomer, to write this post! Other than photographing celestial WHATNOT I haven't even thought of using these terms in many years.

Anyway, it'll be fun.

And probably raining.

[Diredog]

"Attitude" is still the wrong word.  "Attitude" is way of telling how you're oriented to the path you're moving along, and you mostly use it for aircraft and spacecraft.  "If the course is here, and the vehicle is rotated this way, that is it's attitude," put simply.

[Asherah]

MUAHAHAHHAHAHA...


Regarding sextants:

"Its primary use is to determine the angle between a celestial object and the horizon which is known as the object's altitude."




https://en.wikipedia.org/wiki/Sextant


Of course, they're wrong a lot of the time. That's probably a pretty archiac term, but then I'm pretty archaic. I also remember the terms "pitch and yaw" which had something to do with ships or airplanes, but is totally tangential.

What were we talking about?

Oh, yes, the rain...