This is the Skywatch Line for Monday and Tuesday, July 20th and 21st, written by Joe Slomka.
The Sun sets at 8:27 PM; night falls at 10:31. Dawn begins at 3:33 AM and ends with the Sun rising at 5:37.
Monday’s Moon is “New,” which means that it is not visible. Tuesday’s one-day-old Moon rises during daytime and sets at 9:32 PM.
Last week, Jupiter reached Opposition, when it is best for observation. It shares Sagittarius with Saturn and Pluto. Jupiter rises at 12:34 AM, glares with minus 2nd magnitude, appears 47 arc-seconds in size, and sets around sunrise. Monday, the moon Ganymede reappears from eclipse at 11:57 PM; the Great Red Spot is also visible at 11:39 PM. Saturn rises at 8:22 PM and, Monday, is at Opposition. The Ringed Planet shines with zero magnitude, 18 arc-seconds in size and sets after sunrise. Now is the time to observe Saturn in all its ringed glory. A six-inch telescope shows the Cassini Division and moons Titan, Rhea, Tethys, Dione and Iapetus; 8 inch and larger telescopes reveal Enceladus and Hyperion. Saturn and Jupiter retrograde (travel westward) about 8° apart.
Uranus rises in Aries at 12:38 AM, shining with 5th magnitude, and about 3 arc-seconds. Neptune rises in Aquarius at 11:43 PM, glows with 8th magnitude and exhibits 2 arc-seconds. Both set during daytime.
Mars, in Cetus, rises at 11:44 PM, gleams with minus 1st magnitude and appears a large 13 arc-seconds. Mars continues to brighten and enlarge. Mars is about 22° from Neptune and 27° from Uranus.
Venus, in Taurus, rises at 2:47 AM. It is easily spotted near the red star Aldebaran, blazing with minus 4th magnitude, 19% illuminated and 31 arc-seconds. Mercury, in Gemini, brings up the rear, rising at 4:15 AM, zero magnitude and 8 arc-seconds. Mercury attains Greatest Elongation from the Sun on Wednesday, 22° high and 37% lit.
Space probes are very expensive objects, costing millions of dollars to design, launch, and operate. Many probes carry some kind of “fuel” to fulfill their mission. The Wide-field Infrared Survey Explorer (WISE) was launched in 2009. Its “fuel” was coolant, so that its sensitive imagers could detect dim objects. After two years, as expected, WISE ran out of fuel and two of its three cameras would no longer work. NASA ended the mission by shutting down WISE.
However, NASA scientists recycled WISE into NEOWISE, beginning its new mission in December 2013. NEOWISE saved money by reusing something that already is up and working. The third camera is ideal for finding asteroids and comets that are dim and pose a threat to Earth; it doesn’t need to be super cooled. Asteroids emit an infrared glow – the result of heating by the Sun. The magnitude of that glow permits estimates of an asteroid’s size. The wide-field camera samples huge swaths of space, instead of the tiny fields that most telescopes view. NEOWISE is in the hunt for killer asteroids. During its hunt, NEOWISE also discovers comets. Comet NEOWISE, which now blazes in our night sky, is one example of a recycled satellite doing its job.
The comet was first imaged on March 27, 2020. Shortly thereafter it was declared a comet and designated C/2020 F3 NEOWISE. It is a long period comet which took 4500 years to come into our Solar System, and will take 6800 years to leave. Comet NEOWISE is about 5km (3 mi) in diameter. At about 10 PM on Monday and Tuesday night, weather permitting, the comet can be located in Ursa Major (The Big Bear) between the Bear’s front and rear legs. It shines with about 2nd magnitude and is about 20° high in the Northwest (about 315° azimuth). The comet can be seen with the naked eye, and the long tail with binoculars or small telescopes.