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International Observe the Moon Night, Saturday, October 21

by Vinita Domier (

NASA Solar System Ambassador

Davis Astronomy Club will host a special meeting on the evening of Saturday, October 21 to observe NASA-sponsored International Observe the Moon Night starting at 6:30pm at Explorit Science Center (3141 5th Street, Davis). All ages are welcome to this free outdoor annual event where we will observe the Moon, planets, and stars.

Observe the Moon Night reminds us to appreciate the beauty, grandeur, and importance of Earth’s sole satellite. The annual event is held on a Saturday closest to the first-quarter phase of the Moon in September/October when it is ideal for evening viewing. More information about the event and Moon-related activities for all ages are at the following link:

The Moon has played a significant role in most world cultures and religions. Being the Earth’s nearest celestial neighbor, it is a relatively big and familiar object in the sky and easily viewable with the naked eye. Its cyclical movements and ever-changing appearances in the sky have been continuously observed by mankind for eons. Its effects on the Earth’s ocean tides are experienced twice daily, and the Moon plays an important part during lunar and solar eclipses.

The Moon revolves around the Earth in an elliptical orbit at an average distance of 240,000 miles in 27.3 days as seen from the Sun. It also takes 27.3 days to rotate once on its axis as its rotation and revolution are tidally locked, resulting in the same half of the Moon (near side) always facing the Earth.

The near side of the Moon is visible only because it reflects the Sun’s light falling on it. Earth observers see a daily change in the sunlit portion or phase of the Moon. The orbiting Moon goes through a complete phase cycle (new, first quarter, full, last quarter, new again) in 29.5 days as seen from Earth. As the Moon has an extremely rarified atmosphere, there is a huge temperature swing from +260°F to -280°F between the Moon’s roughly 14-day daytime and 14-day nighttime.

The Moon is 27% of the Earth’s size and 60% as dense, resulting in the Moon’s surface gravity being one-sixth of the Earth’s. A person weighing 100 lbs. on Earth will weigh 16.6 lbs. on the Moon. The Moon’s composition is similar to Earth’s, giving credence to the theory that it was created from the debris resulting when a Mars-sized object collided with the newly formed Earth about 4.5 billion years ago.

Our Moon is the only non-Earth place visited by humans thus far. 24 NASA’s Apollo-mission crewmen visited the Moon between 1968-1972, and 12 of them walked on the Moon leaving permanent boot prints on the surface as there is no wind or water on the Moon to erode them. Four NASA’s Artemis II crewmembers are currently training to do a lunar flyby in the near future.

On October 21 evening, the Moon (in Sagittarius constellation) will be at the first quarter phase. We will also observe the very bright planet Jupiter (visual magnitude -2.7 in Aries) rising in the east at 7pm and semi-bright Saturn (+0.7 in Aquarius) that will be overhead around 9pm. (Super-bright Venus (-4.3 in Leo) is visible before dawn).

For more information, please contact Vinita Domier at

Explorit's coming events:

• Explorit is open Fridays from 1-4pm and Saturday and Sundays from 10am-2pm. The current exhibit is “Our WILD World”. Admission is $5 per person, free for Explorit Members and those aged 2 and under.

• Additional public hours during Thanksgiving and Winter Breaks. Check our website for more details

• Now is a great time to donate and help Explorit continue to educate and inspire the scientists of tomorrow:

• A Membership to Explorit grants the recipient free visits to Explorit’s regular public hours, discounts on events, camps, and gives you ASTC benefits to visit other museums throughout the world. To purchase or for more information visit or call Explorit at 530-756-0191.

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