Bakersfield Night Sky - May 7, 2016

Bakersfield Night Sky - May 7, 2016
By Nick Strobel

On Monday, May 9th, we have a rare treat of Mercury transiting the Sun (passing directly between the Earth and the Sun). The last time this happened was back in November 2006. Back then we were able to watch the entire transit. On May 9th, the transit starts at 4:12 AM Pacific Time when the Sun is still below our horizon. The transit will be done at 11:42 AM.

Mercury will appear as a black dot that will be easy to distinguish from any sunspots that might be on the Sun that day because Mercury will be perfectly round and it won't have any gray penumbra around it like you see with sunspots. Also, it will move quickly while the sunspots will be essentially stationary for the seven-hour time period of the transit.

Back in 2006, the transit happened at a very convenient time of day for me to set up the Planetarium's solar scope and show people the transit. The May 9th transit happens during a final exam but I hope I can set up the solar scope and take a look before the final exam. See the William M Thomas Planetarium's website for a webpage about how to observe the Sun safely.

May's free KAS public star party will be next Saturday, May 14th, (if the weather is clear) at Panorama Park from 8 to 10 PM near where Linden Ave intersects Panorama Drive. The Waxing Gibbous Moon will be just one day past First Quarter. The Kern Astronomical Society chooses the Saturday closest to the First Quarter phase for the free public star parties for three reasons. The first is that as seen from Earth, the sunlight is hitting the Moon at a glancing, sideways angle to make the craters really distinctive and "pop out" from the surrounding terrain. This is especially true near the terminator boundary between the day side and night side of the Moon. At Full Moon phase the sunlight hits the Moon more directly as seen from the Earth, so the lack of shadows makes the Moon appear flatter. 

The second reason the First Quarter phase is chosen is that the Moon is high up in southern sky at sunset, so it is "front and center" for that night's show. Because we're so far north of the equator, the Moon's daily-nightly arc from moonrise to moonset will be highest when it is due south.

The third reason the First Quarter phase is chosen is that the Moon is not so bright as to overwhelm everything else in the sky. At full phase the Moon is 8.7 times brighter than at first quarter because much more of the sunlight bouncing off the surface at full phase is bounced back toward the Earth's direction than at the other phases. In fact, at just two days from full phase when the Moon appears about 95% lit up, the gibbous Moon is only about half as bright as the full phase. Another interesting fact is that at third quarter phase when the eastern half of the Moon is lit as seen from the Earth, the Moon is just one-tenth as bright as the Full Moon. The third quarter Moon is dimmer than the first quarter Moon because the eastern side of the Moon has a greater extent of the dark maria.

On the topic of the dark maria, by special request of retired BC track coach Bob Covey I ask you what character or animal do you see when you look at the full Moon? One common character of Western culture is the "Man in the Moon" with northern maria, Mare Imbrium and Mare Serenitatis making the eyes, Sinus Aestuum making the nose, and the combination of Mare Nubium, Mare Cognitum, and part of Oceanus Procellarum making an open smiling mouth. To me it's a bit hard to tell if the character is male or female, so perhaps it would be better to say "Human in the Moon".

In east-Asian many people connect the dark areas to make a rabbit pounding in a mortar and pestle. Mare Fecunditatis and Mare Nectaris make the ears, Mare Tranquillitatis is the head, Mare Serenetatis is the neck and upper body, Mare Imbrium and Oceanus Procellarum are the lower body, and the mortar and pestle are formed from Mare Nubium, Mare Humorum, and Mare Cognitum. The Chinese lunar rover Yutu that landed on the Moon in December 2013 was named after the Jade Rabbit of Chinese poetry from the Han Dynasty period. Aztec and other Mesoamerican mythology also saw a rabbit in the Moon from the same maria but no mortar-pestle.

Those characters always face the Earth because the Moon rotates just fast enough to keep one side facing the Earth as it orbits the Earth. The Moon's near side is locked facing the Earth because of the tidal effects from Earth's gravity acting more strongly on the near side than the far side. This has slowed down the Moon's spin to create the spin-orbit tidal lock. The Moon is working on the Earth's spin in the same way but the Earth's greater mass is making it take a much longer time to get locked to the Moon. About 4.5 billion years ago, the Earth day was less than six hours long. The geologic record shows that by 900 million years ago, the Earth's day had increased to 18 hours long and by 400 million years ago, it had increased to 22 hours long.

All the while the Moon's and the Earth's spins have been slowing down, the Moon has been spiraling away from the Earth. Eventually, (as in 50 billion years from now) the Moon will have spiraled out to where it will take 47 of our current days to orbit the Earth (instead of its current 27.3 days) and the Earth will be locked toward the Moon, so the Earth day then will be 47 of our current days long. This assumes that the Earth-Moon system survives when the Sun becomes a red giant six to seven billion years from now. Another nice example of spin-orbit lock is the Pluto-Charon system visited by New Horizons last July. They keep one face facing the other as they orbit each other every 6.4 days.

On the night of the public star party, the Moon will be just right of Jupiter. Jupiter will be brighter than any other star in the sky. By 9:15 PM, orange-red Mars will be poking above the eastern horizon. Just before the end of the star party, Saturn will rise but being so near the horizon, it will probably shimmer too much to be a good view. The views at the June and July public star parties will be much better! See the Kern Astronomical Society website for a map of the star party location and dates of future public star parties.

Want to see more of the stars at night and save energy? Shield your lights so that the light only goes down toward the ground. Visit the Dark Sky International website for more info.

Nick Strobel
Director of the William M Thomas Planetarium at Bakersfield College
Author of the award-winning website