Another solar system event highlights this weekend, a relatively close encounter with the fourth largest near-Earth asteroid (NEA), 3122 Florence. This 4.4 kilometre diameter rock passed within seven million kilometres of Earth on the morning of September 1. It is fading slowly but will remain within reach of small telescopes over the long weekend. I have seen two NEAs in the past 15 years and consider them to be among my observing highlights, both for the challenge and the uniqueness.
The trick to observing one is ambush it. Get a detailed star map of its path through the sky and pick out an easily identifiable star or group of stars that it will be passing during your observing time. Set your scope on that area ahead of time – then keep watch for a moving star entering the field of view. A smaller NEA making a closer passage can be affected by Earth’s gravity and have its orbit changed slightly, so a wide-field eyepiece helps (higher focal length eyepiece). However, Florence is large and still quite distant (no need to wear a helmet), making orbital perturbations unlikely. It moves among the starry background by about two-thirds the width of the Moon every hour, visible motion at higher magnification when it is near a star. The best time to try for it is around 9 pm Saturday when it passes between the belly and the nose of Delphinus the Dolphin. A map on the Sky & Telescope website [in PDF format] can be found here: http://wwwcdn.skyandtelescope.com/wp-content/uploads/3122-Florence-Chart-B-1.pdf
Delphinus is one of the prettiest constellations and can be seen high in the southeast around 9 pm. It is composed of a small diamond-shaped asterism with a couple of stars tailing off to the right, and it doesn’t take a lot of imagination to picture a dolphin leaping out of the sea. Although its stars are not bright, its compact shape is eye-catching. Below it are the watery constellations of Capricornus, Aquarius, Piscis Austrinus and Pisces. In mythology, Poseidon had designs on the sea nymph Amphitrite but she was afraid and hid from him. The dolphin ratted her out and was rewarded with a place of honour in the sky. The diamond part of the constellation has also been called Job’s Coffin but the origin of this has been lost to time.
This Week in the Solar System
Saturday’s sunrise in Moncton is at 6:41 am and sunset will occur at 7:55 pm, giving 13 hours, 14 minutes of daylight (6:47 am and 7:59 pm in Saint John). Next Saturday the Sun will rise at 6:50 am and set at 7:41 pm, giving 12 hours, 51 minutes of daylight (6:55 am and 7:46 pm in Saint John).
The Moon is full on Wednesday, the Mi’kmaq Moose Calling Moon. Jupiter lies low in the west after sunset as it approaches a conjunction with Spica. Saturn remains in good viewing position in the south after sunset, with its rings proudly on display for telescope users. Venus rises after 4 am now and dominates the eastern morning sky despite being near its dimmest. Mercury, Mars and Regulus can be seen with difficulty within the same binocular field this week, rising about 75 minutes before the Sun.
The Saint John Astronomy Club and RASC NB share a meeting at the Rockwood Park Interpretation Centre on Saturday, September 9 at 1 pm. All are welcome.
Questions? Contact Curt Nason at email@example.com.