a question for those with experience in astro-photography

[sk66]

Actually two:

How can you tell when the moon will appear to be very large...not full vs crescent, but like "harvest moon"?

And should I even care? I suspect this "apparent" largeness is due to magnification by moisture in the air (or similar) and might actually degrade a high magnification photo...

[BryanC]

It is an optical illusion. When the moon is closer to the horizon, it appears larger because it's near objects that the human eye compares it to, as opposed to when it is higher in the sky alone. When it is close to the horizon, and measured it...say by holding something at arms length and making 2 marks to measure the diameter...and then holding it out at same arms length when it was high in the sky, it would be the same diameter.

The difference in color when it is closer to the horizon as opposed to it higher in the sky is because there's more atmospheric conditions you are looking through when it is closer to the horizon.

The distance between the Moon and Earth is variable, but not really discernable by the naked eye.

[sk66]

Originally Posted by BryanC

It is an optical illusion. When the moon is closer to the horizon, it appears larger because it's near objects that the human eye compares it to, as opposed to when it is higher in the sky alone. When it is close to the horizon, and measured it...say by holding something at arms length and making 2 marks to measure the diameter...and then holding it out at same arms length when it was high in the sky, it would be the same diameter.

The difference in color when it is closer to the horizon as opposed to it higher in the sky is because there's more atmospheric conditions you are looking through when it is closer to the horizon.

The distance between the Moon and Earth is variable, but not really discernable by the naked eye.

I can understand that, to an extent. BUT there are times when the moon seems unusually large regardless of position.

[BryanC]

Recently there was an event where the Moon was at it's closest distance in that slight variable I mentioned, and was a full moon at the time. From what I understand, that doesn't happen too much. The apparent size was negligible, but I believe the figure was 30% more light given off.

A 'Harvest Moon' isn't about size, but the timing of moonrise to sunset. Around the autumnal equinox in the northern hemisphere (harvest time), a full moon will rise a little earlier than usual for a few days right at sunset. During this time, there is an overlap between sunlight and moonlight, no total darkness in between. In the past, it gave farmers continuous light of some kind to work their fields.

[candleman]

i know what you mean sk66..
as far as i understand the moons orbit isnt circular, but eliptical, so at times it is physically closer (hence leap tide/spring tide)
as to when thes cycles occur.. i cant answer.

[mseigafuse]

I can't answer your question directly either. But, I use this site as a resource and have found it very helpful:

http://stargazing.suite101.com/articles.cfm

This site is very good too (for planning when to go out to shoot a sun/moon rise/set):

http://aa.usno.navy.mil/data/docs/RS_OneDay.php

I hope those are helpful to you.

[BryanC]

Also...

http://www.moonconnection.com/apogee_perigee.phtml

[mseigafuse]

Oh - I forgot to add this one - http://spaceweather.com/

and this site has some good info too

http://www.luminous-landscape.com/tu...60-night.shtml