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October eNewsletter from the Minnesota Planetarium Society

In this message from the Minnesota Planetarium Society:
President's Message
October Skies
The Moon Illusion
Elliptical Orbits


President’s Message

Planetarium Clears Another Big Hurdle

Great news! On Tuesday, September 23, the Hennepin County Commissioners in their Budget Committee approved proceeding with the Planetarium project, with two amendments. The vote was 5-to-2. We thank Commissioners Dorfman, Stenglein, Opat, McLaughlin, and Johnson for their support.

The amendments added two contingencies that
1) in the event private fund raising efforts failed, the County would not use its bonding authority to raise capital funds for the Planetarium, and
2) that the operating contribution by the City of Minneapolis must at least equal the amount provided by the County.

The issue will now be before the Board of Commissioners for final approval at their next regular meeting on October 7.

Thank you to all who wrote or called your Hennepin County Commissioners or who urged others to do so. We will send out additional information about scheduled votes at both the City and the County soon.

We're on our way!

Peggy Leppik, President MNPS


October Skies

“Wow, what a huge Moon on the horizon!” Look for yourself on October 14 a little after 6pm as the Full Moon rises. Is it really bigger or is your mind playing tricks on you? (see below for more information.) Then around 8:30pm look overhead to see the bright star Vega (pronounced vee ga). Deneb shines to the east while Altair lies to the south, forming the Summer Triangle. The Great Square of Pegasus flies high in the east. Further to the southwest is bright Jupiter. Watch the Moon dance past the king of planets on October 6 and 7.

For early risers, look for Mercury in the latter half of October around 6am about 5 degrees above the eastern horizon. Also around 6am on the 23rd, Regulus lies below and left of the crescent Moon. By the 25th the Moon has glided past Saturn, which will be above it.

For star maps for your location, see http://heavens-above.com .


The Moon Illusion

Most people think the full Moon looks bigger on the horizon than high in the sky--but it's an illusion!  The Moon is just about the same size no matter where you see it.  You can test this for yourself by "measuring" the Moon when it is at each place. Hold out your arm and compare the Moon to the size of your thumb or another finger when it is on the horizon, and then again a few hours later.  Mark your calendars; the best times to do this are shortly after moonrise on:
October 13, 5:30 pm
October 14, 6:00 pm
October 15, 6:30 pm

Scientists cannot agree on exactly why  this illusion occurs. For the best known explanation, try these websites:
http://www.timesonline.co.uk/tol/news/uk/article535931.ece
http://www.lhup.edu/~dsimanek/3d/moonillu.htm


Elliptical Orbits

Although optical illusions change our perception of the Moon's size in the sky, it actually does change slightly due to the elliptical nature of its orbit. The Moon changes its distance to the Earth by about +/- 5%, creating a quite noticeable +/- 10% change in the area it covers in the sky. As the Earth and other planets move around the Sun, they too are in somewhat elliptical orbits, changing their distance on average by +/- 6%. However, planets discovered around other stars have much larger ellipticities (eccentricities), changing by +/- 25% on average. The cause of this is currently unknown. It could be that the formation of our solar system was unusual in this regard, or there could be an extra large mass perturbing the planetary orbits around other stars; one type of candidate is a type of "brown dwarf," an object bigger than Jupiter but too small to start nuclear fusion and become a star on its own.