This Month’s Sky – September 2016


What’s Up in the Sky
AAA Observers’ Guide
By Tony Faddoul

September’s Evening Planets: Jupiter will be in Virgo the Maiden for an hour during the first half of September. Mars will be between Scorpius the Scorpion and Sagittarius the Archer until 11 PM. Saturn will be in Scorpio until 11 PM and setting earlier each night until 10 PM by the end of the month. Bright Venus will be in Virgo after sunset until about 8 PM. Uranus will be in Pisces the Fish and Neptune is in Aquarius the Water Bearer all night. Dwarf planet Pluto is in Sagittarius until midnight.

September’s Evening Stars: Spot the Summer Triangle of Vega in Lyra the Harp, Deneb in Cygnus the Swan, and Altair in Aquila the Eagle. See Antares in Scorpius and Arcturus in Boötes the Herdsman until 10 PM. Look for Capella in Auriga the Charioteer around 10 PM, lingering all night. Find the stars of constellations Andromeda, Cassiopeia, Pegasus, Perseus, Hercules, Draco, Sagittarius, Aquarius, Pisces, Capricornus, and Ursa Major and Ursa Minor (the Big and Little Dippers).

September’s Morning Planets: Uranus will be in Pisces and Neptune can be found in Aquarius. Mercury will be between Leo the Lion and Virgo beginning at 5 AM in the second half of the month.

September’s Morning Stars: Sirius, the brightest star from Earth, will be up around 4 AM each morning and rising earlier by 2 AM at the end of the month. Spot Capella in Auriga and the stars of Aquarius, Cetus, Taurus Gemini, Ori-on, Pisces, Andromeda, Cassiopeia, Aries, Draco, Cygnus, Pegasus, Perseus, and the two Dippers.

September “Skylights”
Sep 1 New Moon 5:05 PM
Sep 6 Moon at apogee (251,700 miles away)
Sep 9 First Quarter Moon 7:50 AM
Sep 16 Full Moon 3:05 PM
Sep 18 Moon at perigee (224,900 miles away)
Sep 21 Mercury stationary 6:00 AM
Sep 22 Autumnal equinox 10:21 AM
Sep 23 Last Quarter Moon 5:55 AM
Sep 25 Pluto is stationary 11:00 PM
Sep 28 Mercury at greatest western elongation
Brightest Mercury of 2016 – predawn
Sep 30 New Moon 8:11 PM


Break Me Off a Piece of that Asteroid

This month, NASA will send the first probe to an asteroid that will bring back to Earth some of its dust. The spacecraft OSIRIS-REx is scheduled to launch from Cape Canaveral, FL on September 8 aboard an Atlas V rocket, and it will return home in 7 years with a sample of the asteroid Bennu.

The Mission

OSIRIS-REx will orbit the Sun for a year and then make a flyby of Earth to use its gravitational field as a slingshot towards Bennu. The probe will begin its approach in Aug 2018, when it will brake to match Bennu’s velocity as it orbits the Sun. OSIRIS-REx will fly in formation with Bennu, surveying and mapping the asteroid and studying its geology to select a sample site.

On Jul 4, 2020, OSIRIS-REx will extend the Touch-And-Go Sample Acquisition Mechanism (TAGSAM), a robotic arm with a sampler head, to collect regolith (surface material). It will touch Bennu for five seconds and release a burst of nitrogen gas to stir up the soil, forcing dust into a collector that holds up to 4.4 pounds. The dust is deposited into a Sample Return Capsule onboard the spacecraft. The probe will then wait until Mar 2021 to start the trip back to Earth, where it will jettison the capsule and deflect itself into solar orbit. The capsule will land in the Utah desert on Sep 24, 2023.

Why Bennu?

101955 Bennu, also known as 1999 RQ36, is a 500 meter-diameter, potentially hazardous near-Earth asteroid that travels 63,000 mph as it orbits the Sun every 1.2 years. A rare, primitive, carbon-rich asteroid with organic compounds, Bennu has not changed much since forming over 4 billion years ago, and it may contain the precursors of life on Earth.

What Does OSIRIS-REx Stand For?

OSIRIS-REx is an acronym of the mission’s main goals and mimics the name of the ancient Egyptian god Osiris. Its full name is: Origins Spectral Interpretation Resource Identi-fication Security Regolith Explorer.

Who are Osiris and Bennu in Egyptian Mythology

Osiris is the god of afterlife, resurrection, and regeneration. His wife and sister, Isis, famously used magic to restore him after he was murdered by his brother, Set. Osiris judges the dead and grants all life, even the fertile flooding of the Nile River. Bennu is a bird deity associated with Osiris. A symbol of creation and rebirth, it rivals the Phoenix in other cultures. It lives on the sacred tree of life.

Sources: nasa.gov; asteroidmission.org; Encyclopedia Britannica.