25 April 2007

Observing Location	VP
Observational Period	1015-1030 EDT
Atmospheric Conditions	Cloud Cover Broken Clouds nearly complete cover but thin cirrus Temperature 58°F Wind Light Breeze Humidity Low Feels Like a little cool There is a possibility of rain showers today and the clouds are beginning to build. Transparency Fair Seeing I
Instruments	Brunton 8x21 compact Binocular w/Welco gold shade 14 welder's filter - Charlie
Observing Party	Charlie Ridgway

Target Sunspots Constellation Ari Category Solar Time yyyymmdd.hhmm 20070424.1015 EDT Comments Distance Light Time 1.005953 AU 8ms Angular Size 31'50.9" Altitude 46.1° Heliographic Latitude (B0) -4.74° Heliographic Longitude (L0) 28.50° Position Angle (P) -25.04° Carrington rotation number (CR) 2055 Nothing to see. Space Weather says an active region is rotating onto the face of the sun but Active Region Explorer shows nothing on the back side but two pores and they are both out to the west.   Groups Spots R North 0 0 0 South 0 0 0 Total 0 0 0 R = (Groups * 10) + Spots)

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I have made another analysis of Moon size vs altitude to see if the movement of the Moon in its orbit during the night would negate its enlargement when overhead. This time I examined the full Moon at apogee (2Apr07) and compared it to the full Moon at perigee (26Oct07).

In both cases the apparent size of the Moon increases as its altitude increases.

In the case of the apogean full Moon the difference between the Moon on the horizon and when it culminates is only 0.73%. The same difference for the perigean full Moon is 1.54%. The Moon only rises half as high on the date of apogee this year as it does on the date of perigee so the difference in size increase is probably a factor of the maximum altitude attained. [i am not sure i said what i mean there and may reword this paragraph on further cogitation]

I also extended my apogee and perigee analysis to five years to see if minimum apogee always coincides with maximum perigee and it does. Now that I think about it that seems logical since the Moon is just moving to opposing extents of the ellipse.

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I got email from Peter today saying he had a gift for me. He had been down to Strand and picked up a copy of Antonin Rukl's Atlas of the Moon for me. It is a great atlas and a lot less frustrating to use than the digital copy of the LAC that I have, which I also love because of its detail, because I can turn from page to page to see adjoining plates and was able to walk the area of the terminator from Tuesday night. I have already roughed out a spreadsheet to figure the colongitude of the terminator based on the tables contained in the book (that information is built into Virtual Moon Atlas and is probably more accurate than my spreadsheet will be).