Fall Connection #4 – Fall Phenomena Q&A

Today’s post features some great questions related to the autumn season of the year, questions we have all wondered about. Interesting stuff! Comments welcome!

Q: What is the Harvest Moon?

A: The Harvest Moon is the full moon closest to the fall equinox. At this time of year the interval between successive moonrises is relatively short in the mid latitudes o the Northern Hemisphere, so we see a full or nearly full moon rising soon after sunset on several consecutive evenings. This bright moonlight allows farmers additional time after sunset to bring in their crops, hence the term, “Harvest Moon.” (Note: this year’s Harvest Moon occurred on September 29 (the Equinox happened on Sept. 22.)

Q: What causes the leaves of deciduous trees to turn color in fall?

During the growing season, leaves contain chlorophyll – a green compound essential for photosynthesis. Chlorophyll absorbs energy from sunlight, and that energy fuels the chemical reaction that converts carbon dioxide and water into carbohydrates (the plant’s energy source) and oxygen. It is chlorophyll that gives leaves their spring and summer green. But chlorophyll itself is broken down by sunlight and must be continually manufactured by the plant – a process requiring sunlight and warm temperatures.

When days get shorter and temperatures begin to drop, chlorophyll production slows and stops. Eventually all chlorophyll disappears from the leaves, revealing the underlying colors produced by substances that remain – anthocyanins give leaves their red color, while carotenoids are responsible for the orange, yellow, and brown hues.

Trees lose their leaves to conserve water and guard against winter freezing. Decomposing leaves add nutrients to the soil, promoting healthy spring vegetation.

Q: At what time of year is the advance of daily darkness the most rapid?

: Near the fall equinox, when three minutes of daylight are lost each day – about 12 times the rate of change that takes place near the solstices.

Q: When do spiders make their biggest webs?

After eating insects all summer, spiders are at their largest – and make their biggest webs of the year – in late fall. Spider silk is made of complex proteins called fibroins, manufactured by the spider’s many different spinning glands. Fibroin production requires the nutrient choline, which the spider also needs for essential physiological processes. Spiders don’t produce choline naturally but must obtain it from their diet. So the spider must budget its available choline between web building and life support.

Q: How do butterflies escape spiderwebs?

Butterflies wings are covered with colorful scales that look and feel like dust. These scales come off easily, helping the butterfly escape the sticky webs.

(The above information came from “The Natureal Year: A Quiz Deck on Ecological Phenomena” by Chris Hardman. The card deck is available through Pomegranate Communications, Inc., www.pomegranate.com  .)

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