StarWatch for the greater Lehigh Valley
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JULY  2020

JULY STAR MAP | MOON PHASE CALENDAR | STARWATCH INDEX | NIGHT SKY NOTEBOOK

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1246    JULY 5, 2020:   Comets are Like Cats…
...they have tails, and they do precisely what they want.” Recent comets, Atlas (C/2019 Y4) and SWAN (C2020 F8), both “crashed and burned” as the saying goes, but there is a new comet on the block. Perhaps the third, Comet NEOWISE (C/2020 F3), discovered in March of this year will prove to be the lucky charm. As I write these words, NEOWISE is rounding the sun at its closest approach. The strange name is an acronym for NASA’s Near-Earth Object Wide-field Infrared Survey Explorer, another satellite among a growing fleet of orbiters and Earth-based telescopes looking for space debris that may hit the Earth. Unlike the crumbling and humbling end of Atlas and SWAN, NEOWISE appears to be holding together and brightening. Astronomers expect it to remain intact after perihelion and appear low in our northeastern sky at dawn later this week, pending no abduction by a large alien spacecraft looking for an easy source of water. Photographed in bright twilight on July 4 with a condensed coma and a short tail, NEOWISE represents a hopeful sign that finally the Northern Hemisphere is getting treated to a naked eye comet worthy of some sleep deprivation. One reason why these recently anticipated comets have been so fickle is that they are all long period gate-crashers. Structural differences and dissimilar dust to ice ratios affect the manner in which a comet appears in the sky. Comets also come in two basic orbital varieties, long and short period. The dividing time frame is 200 years. Those with shorter orbital periods are classified as short period comets, while those with greater orbital intervals get to be called, you guessed it, long period comets. Short period comets come from an area of the solar system known as the Kuiper Belt, that extends from the orbit of Neptune to about 55 times the distance from the Earth to the sun, 55 astronomical units (AUs). These comets have been tamed by the gravitational tugs and pulls of the gas giant planets into orbits which are relatively close to the plane of the solar system and into orbital paths that move in the same direction as all of the planets. Short period comets have seen numerous successful passages around the sun, and through repeated trials by fire, have been structurally strong enough to survive the blast furnace that is the sun. Comets, like Atlas, SWAN, and NEOWISE, were entering the inner solar system from a spherical halo of similar objects called the Oort Cloud. It is thought to be composed of trillions of icy objects at much greater distances from the sun, perhaps up to two light years, where the gravitational perturbations of passing stars can gently nudge a comet sunward to meet its first encounter with Sol. Unfortunately, both Atlas and SWAN failed the test of first passage because their icy structures were too friable, but NEOWISE seems to be holding together. You should be able to catch it by Tuesday, July 7, about 5 degrees above the northeastern horizon under the star Capella, the brightest luminary in that direction and the sixth brightest star of the nighttime sky. You should be at your observing site by 4:30 a.m. Bring binoculars if you have them because, as we all know, comets can be like cats.

[Comet NEOWISE photographed from the ISS]
Comet NEOWISE photographed from the International Space Station near its date of perihelion passage. NASA image...
 

1247    JULY 12, 2020:   See Comet NEOWISE Now!
I have not yet seen Comet NEOWISE, but this week marks its debut into the evening sky which makes its accessibility convenient to anyone who cares to look. At present it is a naked eye object. In addition, each night it will be higher in the sky. The comet survived its passage around the sun on June 3 and has been observed in the morning sky mostly by European astronomers for the past week and by American amateurs who live in locales with exceptionally clear skies. This week mid-latitude regions broaden the scope of a widening range of locales that will be able to view the comet more readily. Currently, because of its low altitude, the extra thick layer of atmosphere that its light must penetrate is dimming the object. Still, the photographs of the comet have been spectacular. I would strongly suggest if you have them, to bring a pair of binoculars along with you to make finding the comet easier and its coma and tail much more spectacular to view. Then try to spot it without optical aid. Several factors are at play with NEOWISE’s brightness. It passed its closest position to the sun, perihelion, on June 3, so unless there is some major structural disruption in the comet’s nucleus which releases large quantities of material, the comet should begin to fade gradually. NEOWISE, however, is a dusty comet, and these types of interlopers always produce the biggest bang regarding a comet’s brightness. It is outperforming predictions and is also approaching the Earth. At its closest position, NEOWISE will be 64 million miles from us on July 22. If a light source halves its distance from an observer, its brightness increases fourfold. That’s something called the inverse square law, Intensity = 1/d2, where “d” equals the distance from the object. The manner in which a dusty comet shines is not through the reflection of its released dust, but because of a process called scattering. Still, the inverse square rule applies. In addition, for the next two weeks, the moon will not be a factor to dilute NEOWISE’s brightness. By the end of this week, the comet will be 19 degrees above the northwestern horizon one hour after sundown and directly under the cup of the Big Dipper. NEOWISE’s height will be equivalent to stacking two fists, thumbs up, above the horizon, high enough to negate most of the fading effects of the air mass through which its light must pass. Adding up all of the pros and cons with respect to NEOWISE’s brightness leads me to predict a solid chance to view the comet with the unaided eye if we have a clear enough evening this week. Current observations indicate that it will rival the brightness of stars of the Big Dipper, but as a diffuse, elongated object. Catch it on Wednesday evening in the NW, if it’s clear, and the comet will be lower, 12 degrees above the horizon, but brighter. Regardless of how the media hypes this comet, I strongly doubt that NEOWISE will be an urban event. Plan to take a little jaunt into the near country on a clear evening. Bring binoculars if you have them, and be prepared to see a traditional looking comet, resplendent with tail, an object that will not return to the nurturing warmth of our sun for another 6800 years. If you ever wanted to view a comet, now is your chance and NEOWISE is your goal. A locator map and pictures are here, https://astronomy.org/StarWatch/July/index-7-20.html#7-12-20. May the tail be with you!

[Comet NEOWISE]
My first attempt to image Comet NEOWISE was simply to practice my rusty astrophotography techniques. Keep it simple was the byword, but the comet was still there. Gary A. Becker image on the evening of July 13...

[Comet NEOWISE]
Comet NEOWISE is now gracing the evening sky, gaining altitude rapidly. The comet does not appear to be diminishing in brightness, but I have not been able to view it without binoculars. Digital photography shows it beautifully with its long dusty tail. Gary A. Becker image on the evening of July 14...

[Comet NEOWISE]
Comet NEOWISE Gary A. Becker image on the hazy evening of July 15...

[Comet NEOWISE]
Comet NEOWISE Gary A. Becker image on the evening of July 17...

[Comet NEOWISE locater map]
Comet NEOWISE climbs higher in the northwestern evening sky during the week of July 12, but becomes just a little fainter. It should remain naked eye throughout this week. The map is drawn for one hour after sundown. Gary A. Becker map using Software Bisque's, The Sky...
 

1248    JULY 19, 2020:   NEOWISE: The Comet That Is, But Isn’t
I have been going to my favorite haunt near my home to photograph NEOWISE, and you can see a map and my images at https://astronomy.org/StarWatch/July/index-7-20.html. Once the page loads, simply scroll down to see the material. No, the picture taken from the International Space Station is not mine, although some of my students have suggested that I apply for astronaut status and permanent residency on the ISS. On Thursday (July 16) a couple stopped who were also on the hunt for NEOWISE. They had binoculars, and I was easily able to point out its location. They were also able to see it with the unaided eye, something that I have been unable to achieve. Fast forward to when I was postprocessing one of my images. The phone rang. “Darn it, Adam, it’s midnight,” was my friendly salutation. He and friends were on Mt. Evans about 50 miles west of Denver. “I know, I know,” he responded. It’s just 10 p.m. here, but I had to tell you how beautiful the comet is.” I then got a live report. “It’s got to have at least a 10-degree curved dust tail and a needle thin, blue ion tail. It’s really stunning.” Everyone was able to see what Adam was witnessing. The curved white dust tail was dominant because of the micron-sized dross being released by this sooty interloper. Light from the sun does not reflect from these particles because they are too small, but some of the energy is redirected in our direction as it passes them, a process known as back-scattered light. The curved structure of the dust tail is actually the larger pieces of grit remaining in the orbital path of the comet. This is easy to see locally with binoculars. The thin, straight ion tail is created by the escaping gases that are the comet’s sublimating ices, going directly from a solid to a gas, while at the same time releasing the dust which is making the comet so spectacular to view. Mainly water, but also containing carbon monoxide and dioxide, cyanogen, diatomic carbon, methane, and ammonia, these simple compounds are ionized by the ultraviolet light of the sun, stripping off their electrons. When an electron gets excited or removed completely from its parent molecule (ionization), then reunites with another positively charged molecule, and descends the energy ladder to a lower state, it can give off visible light as it moves through certain orbital transitions. The ionized gases are being driven rapidly away from the comet in the antisolar direction by the sun’s magnetic field wrapping around and sculpting the charged gas particles into a thin stream. A comet which is mostly ice usually has a greenish, cyanogen-diatomic carbon halo surrounding its nucleus and an ion tail with almost no dust tail at all. However, comets like NEOWISE which have an abundance of dust, geyser it out in continuous eruptions with the escaping gases and become truly dramatic objects in the night sky. So why have you probably not seen NEOWISE when the entire astronomical community is agog with its praises? It is really like that old song, Big Yellow Taxi, “Don't it always seem to go. That you don't know what you've got till it’s gone. They paved paradise, and put up a parking lot.” In the late nineteenth century when the famed American popularizer of astronomy, Garrett P. Serviss, was beginning to complain about the new electric lights in Brooklyn, New York, NEOWISE would have been a resplendent object from even the city. Now with the copious amounts of light pollution that civilization beams into the heavens on a nightly basis, a bright comet has been reduced to a shadow of its true glory. I’m not suggesting that we return to a time when influenza, polio, small pox, TB, cancer, and a host of other maladies reduced US life expectancy to just over 50 years, but I am on the prowl for a trained, suicidal squirrel ready to bite into the right electrical wire and darken the East Coast. During the great blackout of 1965, my friend, Allen Seltzer, took his telescope up to the rooftop of his Brooklyn, NY apartment and had the time of his life, even seeing the Milky Way spanning the sky. Don’t give up on NEOWISE; just use a map and binoculars if you live in light-polluted locales. It’s there, and it’s worth the effort to view, but its “expiration date” is approaching.

[Comet NEOWISE ]
Comet NEOWISE is positioned in the same location as the map printed in last week’s StarWatch for July 18, a nice confirmation that the program used to path its orbit across the sky is accurate. Gary A. Becker image using a light pollution filter…

[Comet NEOWISE ]
This wonderful East Coast portrait of Comet NEOWISE was taken by my friend Peter K. Detterline, an astronomy adjunct at Moravian College. The blue ion tail and curved dust tail are plainly visible in his July 18 evening image of the comet. Note also the greenish color surrounding the coma (front end) of NEOWISE. Peter K. Detterline image…
 

1249    JULY 26, 2020:   NEOWISE, Jupiter, Saturn, and the Moon
If you’ve never seen a comet, your time to view NEOWISE is fading. This week may be your last opportunity to find it easily with binoculars. It won’t be back for another 6800 years. The comet passed closest to the sun on July 3, then on its way out of the solar system, passed closest to Earth on July 22. It was on the 21st that I was able to witness NEOWISE unaided by binoculars from my backyard as an elongated fuzzy patch of sky. Adam Jones, a good friend of mine and former student, observing from Mt. Evans, 50 miles west of Denver, also saw the comet on the following evening. The week before he had reported NEOWISE with a double tail, the dusty section about 10 degrees in length and the ion (gas) tail a little longer. A week later, the comet was much more subdued, but still visible with a double tail from clear western skies. The comet this week is to the left of the Big Dipper in the constellation of Ursa Major, the Great Bear, and is still climbing higher into the western sky. On Wednesday, July 29, it passes into the constellation of Coma Berenices. By 10 p.m., it is still nearly 30 degrees above the WNW horizon, setting at almost 1 a.m. the following morning. View a map for NEOWISE here at https://astronomy.org/StarWatch/July/index-7-20.html. Simply scroll down to find the drawing. After your hunt for NEOWISE, turn around and look towards the southeast, and you’ll be greeted by two bright starlike objects, Jupiter, the brighter and to its left and lower, the ringed planet Saturn. If you point your binoculars towards Jupiter and hold them securely, you may be able to detect two of Jove’s four Galilean satellites, Ganymede and Callisto, looking like faint stars hugging the planet. Discovered in 1610 by Galileo with one of his homebuilt refractors, actually the highest quality of the time, their motion around Jupiter bolstered the Copernican hypothesis that the planets revolved around the sun. Both Jupiter and Saturn were opposite to the sun (in opposition) during the past two weeks, Jupiter on July 14 and Saturn six days later on July 20, the 51st anniversary of Armstrong’s walk on the moon. This means that both planets are becoming better positioned for evening viewing, rising about four minutes earlier each day, but still low in the SE in the early evening. Eventually, Jupiter will catch up to Saturn, since it is closer to the sun and moving more rapidly in its orbit. The two planets will be in conjunction, only 1/10th of a degree apart on the winter solstice, December 21, low in the southwest as darkness falls. While you have your binoculars handy this week, give a quick look at the moon which will be at first quarter early Monday, waxing gibbous throughout the rest of the week, and full by August 3. A myriad of objects awaits your view in the evening sky this week, and there is more to come with Perseid meteors “flying” at their best on the morning of August 13.

[Comet NEOWISE locater map]
Comet NEOWISE climbs still higher in the northwestern evening sky during the next two weeks, but it is fading. The locater map is drawn for one hour after sundown. Gary A. Becker map using Software Bisque's, The Sky...
 

[July Star Map]

[July Moon Phase Calendar]
 

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