This is the Dudley Observatory Skywatch Line for Wednesday, March 18th, and Thursday, March 19th, written by Louis Suarato.
The 28% illuminated, waning crescent Moon sets at 1:32 p.m. Wednesday, and rises at 4:59 a.m., Thursday. At 8:30 p.m., Venus will be 30 degrees above the western horizon. Venus reaches perihelion on Thursday, its closest distance to the Sun during its annual orbit. Eccentricity measures the degree to which a planet deviates from a circular orbit. An eccentricity of “0” is a circular orbit, and an eccentricity of “1” is a highly elliptical orbit. Venus has the least elliptical orbit of any planet. Venus eccentricity is .007, giving it the least difference in distance between aphelion and perihelion of 910,836 miles. The planet with the highest eccentricity is Mercury with a degree of 0.2056. The difference between Mercury’s aphelion and perihelion is 14,873,929 miles. Venus is the slowest rotating planet in the solar system, spinning at only 4 miles per hour. By comparison, Earth rotates about 1,000 miles per hour. Venus is also he only planet to rotate clockwise.
Utilize the dark skies to observe the Andromeda Galaxy approximately 40 degrees to the northwest of Venus. Thursday morning provides an opportunity to see at least three planets and the crescent Moon. Jupiter is the first to rise at 4:07 a.m., followed by Mars 2 minutes later. The two outer planets will be a degree apart. Saturn rises next at 4:29 a.m., followed by the crescent Moon a half hour later. Use binoculars to attempt to see Mercury above the east-southeastern horizon around 6:40 Thursday morning.
The vernal equinox, or astronomical spring, occurs in the northern hemisphere at 11:50 p.m. Thursday. During the equinox, the Sun crosses the extension of Earth’s celestial equator going from the southern to northern hemisphere. The word equinox translates to equal night, indicating the time of year when, at the equator, the number of daylight hours equal the number of nighttime hours. This is also the time when the terminator on Earth is perpendicular to the equator, equally illuminating both southern and northern hemispheres. The equinox is the only time when the Sun rises in one rotational pole, and sets in another, temporarily putting both poles in daylight. The vernal equinox is also the time when the northern hemisphere begins to tilt toward the Sun, shortening the distance between the Sun’s rays and Earth, and gradually warming the northern hemisphere.