Supermoon

[jambouk]

How much bigger is the apparent diameter of a full moon at perigee compared to a full moon at apogee?

The internet is littered with various numbers (4-20% bigger), but I'm not clever enough to work it out for myself. 

Thanks for any replies.

James

[brantuk]

When I last saw a super moon it appeared 2-3 times bigger than it's regular size when it was near the horizon - then get's smaller the higher it goes. It was amazing that night cos conditions were just right.

[Stu]

From some quick searching through SkySafari, I found a range of sizes from 29.6 to 33.8 arc minutes over the next year or so. That would make it around 14% bigger at perigee than apogee. This will vary a fair amount I'm sure.

Appearance of being much larger when near the horizon is an optical illusion though. I confess to disliking the term 'super moon', it seems like a media hyped kind of thing.

[michael.h.f.wilkinson]

At perigee, the moon appears some 5.8% bigger in diameter than the average disk size. It is 11.6% larger in diameter than at apogee, In terms of the apparent surface on the sky, these figures are 11.9% and 24.5% respectively. These figures can readily be computed from the perigee (363,396 km), apogee (405,504 km) and average (384,500 km) distances to earth. The effect Brantuk describes is essentially an optical illusion. The sun and moon appear larger when low in the sky

[brantuk]

Yup - I should have mentioned it was an optical illusion at the horizon (for newcomers) - but I do know jambo personally and I'm sure he's aware of the phenomenon. A super moon at the horizon was my real point - it's a truly amazing sight in the right conditions - I was dead lucky to have seen it that night - a "once in a lifetime" experience. Thanks for adding the measurements - I'd have no idea how/where to get those.

[Stu]

At perigee, the moon appears some 5.8% bigger in diameter than the average disk size. It is 11.6% larger in diameter than at apogee, In terms of the apparent surface on the sky, these figures are 11.9% and 24.5% respectively. These figures can readily be computed from the perigee (363,396 km), apogee (405,504 km) and average (384,500 km) distances to earth. The effect Brantuk describes is essentially an optical illusion. The sun and moon appear larger when low in the sky

Are those numbers averages Michael? This site, which I assume is accurate has quite a variation.

http://www.moonsighting.com/perigee-apogee.html

[Stub Mandrel]

According to Sky and Telescope the lunar eclipse on the 27 September will be the 'biggest you will ever see' because the moon will be so close.

http://www.skyandtelescope.com/astronomy-news/observing-news/get-ready-for-septembers-total-lunar-eclipse-091420155/

This says 13% larger on diameter than the April eclipse, which is over 27% larger in area. I suspect that's where the two different ranges of size variation come from.

[michael.h.f.wilkinson]

My numbers are indeed averages.

[niallk]

Yup - I should have mentioned it was an optical illusion at the horizon (for newcomers) - but I do know jambo personally and I'm sure he's aware of the phenomenon. A super moon at the horizon was my real point - it's a truly amazing sight in the right conditions - I was dead lucky to have seen it that night - a "once in a lifetime" experience. Thanks for adding the measurements - I'd have no idea how/where to get those.

I love the moon-horizon illusion! A magical effect reminding us of the mysteries behind how our brains work...

[jambouk]

Thanks all for the comments and help and links.

James

[Dave In Vermont]

Here are two quick articles on the subject of "super" and "micro" Moons:

http://www.timeanddate.com/astronomy/moon/super-full-moon.html

http://www.timeanddate.com/astronomy/moon/micro-moon.html

Hope it helps,

Dave

[Victoria1410]

Here are two quick articles on the subject of "super" and "micro" Moons:

http://www.timeanddate.com/astronomy/moon/super-full-moon.html

http://www.timeanddate.com/astronomy/moon/micro-moon.html

Hope it helps,

Dave

These articles are awesome    thanks for the links

[Stub Mandrel]

Dave, your link confirms that the eclipse next week will be a 'supermoon' :-)

[JamesF]

So I shouldn't have been telling people that the Moon looks bigger when it's close to the ground because it isn't as far away as when it's high up in the sky?

Oh!  I feel such a fool now!

James

[Peter Drew]

If you spread your legs and look through them with your head upside down at the Moon when it's near the horizon it appears to shrink to its normal size. (The Moon that is!  ).

[Stu]

If you spread your legs and look through them with your head upside down at the Moon when it's near the horizon it appears to shrink to its normal size. (The Moon that is! ).

, funny

[JamesF]

If you spread your legs and look through them with your head upside down at the Moon when it's near the horizon it appears to shrink to its normal size. (The Moon that is!  ).

I'm only half certain that you've made that up to see how many people will admit to trying it

James

[Pig]

If you do it with no pants on at all it would most certainly be a super moon

[JamesF]

If you do it with no pants on at all it would most certainly be a super moon

[Peter Drew]

Joking apart, it really is so. The Moon appears larger at or near to the horizon because of your normal frame of reference, when you are facing upside down this changes the perspective.