• Sara Thompson

Look up for International Observe the Moon Night

by Vinita Domier (vcdomier@yahoo.com)

NASA Solar System Ambassador

Saturday, October 1, is NASA sponsored International Observe the Moon Night. The Davis Astronomy Club will be hosting a special meeting on October 1 starting at 7:00pm in front of the Explorit Science Center (3141 5th Street, Davis) to commemorate this annual event. All ages are welcome to this free outdoor star party where we will observe the Moon, planets, and stars.

International Observe the Moon Night reminds us to appreciate the beauty, grandeur, and importance of Earth’s sole satellite. The event is held on the Saturday closest to the first first-quarter phase of the fall Moon when the Moon is ideal for evening observing as it is overhead at sunset and sets around midnight. More information about the event and moon activities for all ages can be found at https://moon.nasa.gov/observe-the-moon-night/.

After the Sun, our Moon is the most prominent and brightest object in the sky. It is 27% (about a quarter) of the size of the Earth and 60% less dense, resulting in the Moon’s surface gravitational force being only 16.6% (about one-sixth) of the Earth’s. The Moon is our nearest neighbor in the solar system, revolving around the Earth in an elliptical orbit at an average distance of only 240,000 miles.

The Moon takes 27.3 days to rotate on its axis and that is equal to the time it takes to revolve around the Earth as seen against the background stars (its sidereal period). This results in the same half of the Moon (near side) always facing Earth and the other half (far side) never visible from Earth. The Moon has an extremely rarified atmosphere with no wind or water on the surface to cause any appreciable erosion, and has extreme daytime and nighttime temperature swings from +260°F to -280°F.

The Moon is visible to us on Earth because it reflects the Sun’s light falling on it. While half of the Moon is always bathed in sunlight and the other half is always plunged in shadow, observers on Earth see different parts of the Moon illuminated as it orbits around Earth. The changing shapes of the sunlit portions of the Moon are known as its phases and it goes through a complete cycle in 29.5 days (its synodic period) as seen from Earth.

The Moon is also responsible for solar and lunar eclipses visible from the Earth. Solar eclipses can occur when the Moon is between the Sun and the Earth (new moon phase) and lunar eclipses can occur when the Earth is between the Sun and the Moon (full moon phase). Eclipses do not happen at every new/full moon because the Moon’s orbital plane is tilted at 5.15° to the Earth’s orbital plane. The next total lunar eclipse visible in its entirety from Western USA will be after midnight on November 8, 2022.

On October 1 evening, the Moon (in the Ophiuchus constellation) will be close to the first quarter phase.

We will also observe the very bright planet Jupiter (visual magnitude -2.8 in the Pisces constellation) and semi-bright Saturn (visual magnitude (+0.5 in the Capricornus constellation) in the southern sky. Now is the best time to view Jupiter as opposition, when a superior planet is visible all night because it rises when the Sun sets and sets when the Sun rises, was on September 26. Co-incidentally Jupiter made its closest approach to Earth in 59 years during this opposition, resulting in Jupiter appearing bigger and brighter in the night sky.

Exploit's coming events:

• Explorit is open to the public on Fridays from 1-4pm, Saturdays and Sundays from 10am-2pm. Admission is $5 per person. Explorit Members, ASTC, and those age 2 and under free.

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