Just a quick note to remind folks that the 19th of March 2011 is the night of the Lunar Perigee, which is the point in the moon’s eliptical orbit when it comes closest to the Earth, closer than it’s been in the last twenty years. It’ll be about 15% larger and brighter in the sky that normal – I’ve got my telescope out and my fingers crossed for clear skies :-)
I saw the dress rehearsal last night.
good thing too. last night was overcast.
According to Neil Degrasse Tyson, the last time was actually in 2008:
Cost of laying off your science staff: @CNN reports the last full moon w/perigee was 1993. Actually, last time was Dec 2008
Don’t forget – it’s a full moon at perigee (as Hans comment alludes to) – that’s what makes this rare(r)…
I don’t see where the oft-repeated figure of 15% larger and brighter comes from. It does not follow from the minimum and mean distances of the moon in its orbit. The angular diameter is inversely proportional to the distance, so:
Mean dist/minimum dist = 1.056 (about 5.6 % difference in diameter, or 11.6% change in area/brightness).
The numbers are even farther off if you compare the apparent lunar diameters at minimum and maximum distances (11.6% difference in diameter/24.6% difference in area/brightness).
I think 15% is some kind of internet meme that nobody bothers to check.
Well, I’m still excited about it :p
It is very beautiful. The sky is clear here as of 4 a.m. and there is a light frost on the ground to reflect the moonlight. The effect is really quite striking.
@Ursa-
You crack me up!
I have always wondered how percentages are determined. *Kills 99.9% of germs* Says who? *Lasts 50% longer* Than what? *15% better mileage* Get real. There are way too many variables to be able to assign an exact percentage.
I must admit here that I realize there are probably fewer variables when it comes to something like planetary movement. 15% just sounds about right to them.
@Custador-
Break out the surf boards!
I think my favorite is “The average funeral can cost up to $9000.” If you can’t see what’s wrong with that sentence, the court should appoint a guardian to manage your affairs for you, as you are not competent to reason your way out of a paper bag.
And the hair clippers. Lycanthropes should brace themselves for a 15% increase in hirsuteness tonight.
Oh, dear; I may have to have someone take care of me, because I think I see what’s wrong with the sentence…here’s my stab at it:
1. What is that figure based on?
2. “Can” isn’t used when talking about an average
3. Also, since funerals happen all the time, it’s virtually impossible to determine what an “average” funeral would cost–you can never determine the intermediate quantity.
Math fail. Sorry. If it can be calculated at all, an average is a single, discrete value. It cannot vary “up to” some other value.
“The average funeral costs $9000″ is acceptable. This statement has meaning.
“A funeral can cost up to $9000″ is acceptable. This statement also has meaning.
“The average funeral can cost up to $9000″ is nonsensical, but apparently it doesn’t have to make sense to be effective in a world where most of your target market for funeral insurance is innumerate.
So should the court appoint a guardian to manage my affairs for me?
Tsk, tsk. Maybe on a provisional basis, at least until such time as you complete a court-ordered course in elementary statistics. Don’t fret, I’ve heard that they’ve made many advances in the way the subject is taught since I suffered through it. Fewer than 10% of students go mad as a side effect these days.
Looked like a full moon to me. I like that I always see a rabbit in the full moon.
Right now the moon is about 40° above the horizon. It’s quite bright. Seems like I’ve seen it larger before. The sky looks especially brighter than usual, too.
There also seems to be an aura around the moon, or is that the beer and catnip making me see that?
Take a wild guess (hint: there’s no aura).
Actually, this full moon’s apparent size is only about 1/2 of one percent larger than last month’s full moon. Which was only one day away from last month’s perigee. The 15% figure is the difference in apparent size from perigee (when the moon is closest to the Earth in its orbit) and the apparent size at apogee, when the moon is farthest from Earth in its orbit. That 15% difference happens every month. This month, it just happens to be a full moon when it is at perigee.
That explains a lot. It looked no bigger than I have often seen it before.
Except that 15% isn’t the right number, it’s some kind of unkillable internet meme.
Lunar perigee distance = 364,397 km
Lunar apogee distance = 406,731 km
The ratio of apogee/perigee gives you the increase in the apparent diameter according to the small angle formula. This is 1.12, not 1.15.
Either way, the moon last night was really big and bright. It looked great.
The big was largely an optical illusion (I was expecting it, the moon was physically a little closer, the sky was amazingly clear, I expressly looked at times when there was something to compare it to and my memories of the last full moon were affected by my expectations of this one) and the bright was breath-taking. Luckily, I’d locked the doors and windows, and hidden the key where I could only get to it with small, dexterous fingers – not the big clumsy claws I usually have at those times.
Can’t wait for this evening :-)
Actually, if the Moon’s area increases 12% due to it being closer to Earth, its luminosity will increase by more than 12%, due to the inverse square factor of light scattering.
Since the Moon is not a point light source like a star I don’t know the formula for calculating its luminosity as a function of its distance to us, but I find it reasonable to believe the increase is somewhere around 15%.
Notwithstanding a number of factors, such as:
- The distance differs by 12% between apogee and perigee, so it’s clearly incorrect to say that the Moon is 12 (or 15)% brighter than normal (since “normal” is the average distance which is only 6% different from apogee). It would be more correct to say that the Moon is 12/15 % brighter than it is when it is at its furthest distance to us, but of course this doesn’t sound as sexy.
- The Moon’s position over the horizon may influence the luminosity (at least in the visible spectrum) a lot more than its distance to Earth. IIRC it may even affect its apparent size.