Bakersfield Night Sky — June 2, 2024
This morning a thin waning crescent moon was about half a fist-width at arm’s length to the right of Mars. This beautiful pairing was first visible in the east by about 3:45 a.m. with the moon rising about 20 minutes before Mars. This time was about ten minutes before astronomical twilight (or astronomical dawn) began, so the sky was still plenty dark. Saturn rises about 1.5 hours earlier than Mars, so it is already two fists at arm’s length above the southeastern horizon by 3:45 a.m..
Astronomical twilight is when the sun is between 18 and 12 degrees below the horizon and there’s some skyglow that washes out the faint diffuse objects like galaxies and nebulae and the faintest stars can’t be seen. Those in the city with all of the street lights and other light pollution won’t notice any change because the sky always has a skyglow. The next stage of twilight dawn is nautical twilight when the sun is between 12 and 6 degrees below the horizon. The horizon is now visible, so the altitude of bright stars above the horizon can be measured with a sextant (an important navigation device used at sea before we had GPS satellites). The final stage of twilight dawn is civil twilight when the sun is less than six degrees below the horizon and there’s enough sky light that artificial light is not needed.
This morning’s astronomical twilight (dawn) began at 3:56 a.m., nautical twilight began at 4:36 a.m., and civil twilight began at 5:12 a.m. This evening the sequence will reverse itself with civil twilight (dusk) extending from sunset to 8:36 p.m., nautical twilight going to 9:12 p.m., and astronomical twilight ending at 9:53 p.m.
The next pairing of the moon with something bright will be the evening of June 8 when a waxing crescent moon will form a triangle with the brightest stars of Gemini, Pollux and Castor, low in the west-northwest. By the end of nautical twilight (about 9:17 p.m. for June 8), the moon will have moved to be directly below Pollux, forming a right triangle and the moon will still be about a fist-and-a-half above the horizon. With the moon just 8% illuminated, it should make a nice photo!
Less than two weeks ago, the most distant spacecraft, Voyager 1, resumed sending us science observations of interstellar space, more than four times farther from the sun than Pluto. Launched in 1977, Voyager has taken 47 years to get to this record-setting distance but it has a long, long way to go to become truly interstellar. The nearest star, Proxima Centauri, is about 6767 times farther away from the sun than is Pluto and Voyager is not heading anywhere near the direction of Proxima Centauri. I have a picture illustrating the difference between Pluto's and Voyager's distances compared with Proxima Centauri's distance near the bottom of the "Size Scale" page on my Astronomy Notes website.
The boundary of interstellar space is where the outward pressure of the solar wind (charged particles constantly flowing outward from the sun) is matched by the pressure of charged particles in the interstellar medium, called cosmic rays, that were spewed out by massive stars exploding as supernovae long ago. Last November, Voyager 1 went through a denser patch of charged particles that knocked out one of Voyager’s memory chips in the flight data subsystem, causing Voyager to send back nonsensical gibberish. The charged particles were probably interstellar cosmic rays but there is the possibility that the increase in charged particles were the result of a wave reverberating from a surge in the solar wind pressure hitting the interstellar cosmic rays.
At Voyager 1’s distance, radio waves traveling at the speed of light take over 22.5 hours to go from Earth to Voyager 1, meaning it takes about 45 hours to get a reply to any message or command we send to Voyager 1. NASA engineers working with this huge time delay took a while to locate the problem (the dead memory chip) and then to redistribute the dead chip’s functions across the remaining memory chips, already pretty well-packed with their own coded functions. Remember that we’re dealing with 50-year old computer technology, so memory space is extremely small! Voyager 1 has about six years of electrical power left from its Radioisotope Thermoelectric Generator unit.
Closer to home is an example of finding treasures in the data archives of missions from long ago. The Magellan mission mapped the surface of Venus in the early 1990s. The images Magellan created with its synthetic aperture radar are still the most detailed of Venus over 30 years later. Examining radar data from the Sif Mons volcano in Eistla Regio and another volcanic area in Niobe Planitia taken in 1990 and in 1992, an Italian team found changes that could be explained by the formation of new rock from lava solidified in eruptions that occurred between those two times. Both regions combined added about 30 square miles of rock between 10 and 66 feet deep to the surface. Adding this discovery to the discovery in 2023 from the Magellan archive of another volcanic eruption shows that Venus is about as volcanically active as Earth.
The VERITAS mission that will launch to Venus in the next decade will be NASA’s follow-up to Magellan. It will have an improved synthetic aperture radar mapper and near-infrared spectrometer to map the surface topography and composition in greater detail. Extremely precise measurements of VERITAS’s motion will measure the lumpiness of Venus’ gravitational field, revealing its interior structure.
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Director of the William M Thomas Planetarium at Bakersfield College
Author of the award-winning website www.astronomynotes.com
