TGT #33 - Throwing a DART Successfully, Part 2!; + 6 more [Oct. 16, 2022]
Cover Story--How to Defend a Planet; Sky Planning Calendar--Moon Covers Mercury...and the Sun (Depends on Where You Are); Online Calendar Debuts; Astronomy in Everyday Life--400 Year Old Baseball?
Cover Photo - An Asteroid Pair by Radar
In This Issue:
Cover Photo — An Asteroid Pair by Radar
Welcome to Issue 33!
- The Galactic Times’ Online Sky Planning CalendarThrowing a DART Successfully, Part 2! Or, How to Defend A Planet (Cover Story).
Sky Planning Calendar —
* Moon-Gazing -
- Mercury Covered by Moon before Vanishing Into Solar Glare
- New Moon Brings Partial Solar Eclipse to Europe* Observing—Plan-et - Two Planets Change Directions, Two Disappear
* For The Future - Lunar Eclipse Next Month
* Border Crossings - No Crossings, Just Different ‘Signs’Astronomy in Everyday Life — The 400-Year Old Baseball Player?
The Classroom Astronomer Newsletter - Inbox Magazine Issue 37 Highlights!
Welcome to The Galactic Times Newsletter-Inbox Magazine #33 !
In this Issue we conclude our look at the DART mission with information from the Division for Planetary Sciences meeting on the results we might expect from one—or more!—DARTS hitting an asteroid. Can they do the job, or just shatter the world into more colliding pieces? PLUS, the news on its success just as we were going to print!
Two interesting sky happenings, depending on where you are….Mercury gets covered up by the Moon, and so does the Sun one day later. But you need to be in different places to view them. See the Sky Planning Calendar.
As previously mentioned, we have added an online version to our Sky Planning Calendar to our Home Page! It has taken a bit to learn its ropes and we’re just now starting to add illustrations to it, but here is a look at the text version of the Online Calendar, which you can get to by going to www.thegalactictimes.com and selecting the leftmost menu option, and then the lowest menu choice.
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Some changes to The Galactic Times are anticipated, starting next month. Among them, adding The Galactic Times InDepth publication. Stay tuned to your Inbox…..
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Click here https://www.thegalactictimes.com for our Home Page, with all past issue Tables of Contents and stories indexed by topic. You can also hear and find useful materials for education from our former podcast on the website (plus links to other Hermograph products and periodicals).
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School is now in session. Educators, a hot topic is atomic and stellar spectroscopy. Do you want an easier way to see gas tube spectra that don’t involve those plastic triangular spectroscopes, with the film that gets out of place, with scales that should be by sine-theta instead of theta, and you look at both the target and the spectrum in the same direction instead of aiming one direction but looking for the spectrum in another? Then you should purchase a set of Hermograph The Classroom Astronomer’s Spectrum Viewers for Elements, Mixtures and Molecules! With 15 gas tube spectra, photographed through the same film, and printed on both sides, with a large viewing window.
For more information and purchase links, go to https://www.hermograph.com/spectrumviewers.
Thanks!
Publisher — Dr. Larry Krumenaker Email: newsletter@thegalactictimes.com
Throwing A DART Successfully, Part 2! (Or, How to Defend a Planet).
On Monday September 26, 2022 NASA successfully crashed a small spacecraft named DART into the moon, Dimorphos, of an asteroid, Didymos. The previous issue of The Galactic Times discussed the historic event in some depth, the purpose of which was to test out whether this size probe, crashing into the tinier of the two worlds, could shift its orbit. If it could, then we can push a real, potentially Earth-colliding asteroid out of its path towards us—Planetary Defense. Or can we?
So there are two questions now to ask:
What do we hope to see from the mission?
And what are the real chances of success?
Last week’s meeting of the AAS Division for Planetary Sciences had several sessions devoted to Planetary Defense. The answers may be seen in two of the presentations.
Dr. Shantanu Naidu of the Jet Propulsion Laboratory plans radar monitoring of the double asteroid for the second half of October using the Goldstone 70-meter and Green Bank 100-meter radio telescopes. The smaller moonlet barely shows up in radar images (see the Cover Photo).
But images are not what is really wanted. It is orbital speed and positions. Where Dimorphos should be is known. Where it ends up after DART gave it a kick earlier this month is where we want to find out.
In the chart above are predictions where Dimorphos should be if there is no effect from DART (yellow crosshair), if there is only a small effect from DART (green crosshair), or a large effect (red crosshair) as it accumulates over a three-week period. The larger the kick, the more the moonlet gets farther away from its normal predicted period.
But is it the kick that the probe gives it that actually does the job?
His colleague, Dr. Paul Chodas, points out that DART was moving at a speed of 6.1 kilometers per second and weighed 570 kilograms. Dimorphos was a solid rock of 160 meters in size (‘solid’ is a relative term; it could be just a gravitationally bound rubble pile). Find the density of a stone in any geology book, compute the mass of the moonlet, and do a Physics 101 momentum exchange collision problem here and you will find that the change in the moon’s velocity is a minuscule few millimeters per second. The delta-V of the Dimorphos-Didymos system would be about 100 times smaller! Is this likely to make a difference if the object were targeting Earth? Not likely!
But there is a second source of momentum change not accounted for here. As noted in photographs, there was more than a push, there was a whole lot of ejecta fired off from the surface as well. This formed a secondary rocket blast that would add to the moon’s change in speed. By how much? Greatly uncertain right now. Perhaps those radar values will help find out. It could be anywhere from 1-10X the DART push.
Meanwhile, a real colliding threat might need more than one push, perhaps 15 DARTs. An expensive proposition! And with an additional danger. You might just break up the target into multiple colliders heading towards Earth.
According to Dr. Chodas, a successful deflection will also need a lot of lead time…..
What will be the net result? Probably not what we want….here’s his chart.
In almost most cases, what will happen is the asteroid will be disrupted, i.e. broken up into pieces. We will need a LONG time frame, years, even decades for multiple hits onto the object to have it miss us by 1 Earth radius without disruption. His suggestion is that we need instead is to develop some kind of slow-push technique, such as an ion-beam deflection (or perhaps an attached rocket?) to do the job.
Added in press: NASA announced this past week that Dimorphos’ orbital period changed by a whopping 32(!) minutes, more than four times Naidu’s grandest hopes. Whether that was because the moonlet was less massive or the ejecta was more a rocket booster than expected, or some other reason is not yet known.
Sky Planning Calendar
Other than for Venus, October is pretty much the start of the best evening viewing period of the year! Venus will join the show better in January 2023. Meanwhile, here is what is available for the second half of October!
Moon-Gazing
Moon passages by a star, planet or deep sky object are a good way to find a planet or other object if you’ve never located it before.
October 17 Last Quarter Moon AND Apogee. A Micro-Half-Moon during the morning hours! Can you tell?
October 24 The Moon passes over (occults) the planet Mercury for US/Canada observers east of a line connecting approximately Austin and Kansas City to Chicago, Toronto, and Montreal. Observers will see the reappearance out of the darkened lunar limb (which is most of the Moon as it is just one day before New Moon). The reappearance takes place between 15:00 and 16:00 UT (Universal Time), depending on where you are observing from which translates to 11 AM and noon Eastern Daylight Time, 10-11 CDT, as early as 10-14 minutes after the hour near Austin/KC/Montreal, to about 10 minutes before the next hour near Miami. You’ll have to watch carefully with a telescope and avoid at all costs looking at the nearby Sun!
October 25 New Moon and a Partial Eclipse of the Sun….but not in the continental North America. See below.
October 29 Perigee. A Super-Sized Evening Crescent!
October 31 A First Quarter Moon but only for the Pacific Coast and points westward. All others, November 1st.
Observing---Plan-et
The ancients all but believed the planets were on geared spheres above us. You can almost hear some of them screeching to a halt these two weeks! Of the four bright visible planets, one comes to halt and begins retrograde motion, while another comes to a halt and stops retrograding. A third planet is bright but diving into the solar glare while the missing fifth world is impossible to find.
Let’s take them in reverse planetary order.
Saturn, the least bright of the major naked eye outer worlds, is still easily spotted well to Jupiter’s west. It ceases its westward motion on the 23rd and sets around midnight standard time, no longer a morning object.
Jupiter is shining brilliantly in evening prime time, visible from within evening twilight time to just before morning twilight begins. At magnitude -2.9 it far outshines everything at night but the Moon.
Mars is stationary on the 30th, beginning its retrograde motion from between Taurus’ horns and heading westward eventually well past its head. It rises after evening twilight has ended but it is unmistakable, a red star nearing magnitude -1.2 at month end, and still brightening.
Venus is in a time-out, in conjunction with the Sun on the 22nd, and won’t start to even make a glimpsing appearance until around Christmas.
Mercury starts these two weeks visible at least 45 minutes or more before sunrise but that ends by the 27th. Note the occultation of Mercury by the Moon on the 24th, described above. If you get up before dawn, at least 30 minutes before Sunrise, you will see the very thin crescent Moon just barely above the brighter than average planet, essentially a celestial almost-Mercurian symbol of itself - ☿!
And for those seeking something closer to home….
On the 21st, the Orionid meteor shower will peak. Actually it peaks during the day so the dawns on the night before and the night after will be about equally filled with meteors. Plus, with the Moon midway between Last Quarter and New Moon, and the best hours to see these meteors are the darkest hours before dawn, the fat crescent Moon will not be too much of an interference. The general rate is about 20 meteors per hour and they are generally fast and bright and leave trails. You can see some even on nights before and after, but in much fewer amounts.
About that partial solar eclipse…..
The Moon’s shadow will be skimming the Earth’s surface and not covering the whole solar disk anywhere. The only parts of North America that will see anything will be the eastern shoreline of Greenland and the island of Iceland, which will see a tiny notch of sunlight on the Sun’s edge at or near sunrise as it leaves the Sun’s disk. The greatest coverage, 96%, takes place at sunset in far north central Russia. Europeans will see from 0 to 60% coverage during midday, roughly two hours of eclipsing centered around noonish; Asia ditto but a bit later.
For the Future
A total lunar eclipse will occur on November 8. North Americans will see all or most of it, depending on whether you are closer to the West or Eastern sides of the country. Ditto NE/Central Asia, Australia, Central America and parts of South America. Most of Europe and all of Africa, sorry, nothing. More details in the next TGT.
Border Crossings
The Sun is in Virgo until October 30th, and enters Libra the Scales on Halloween (BOO!) whereas tradition says it was already there …. until the 22nd and had entered the much bigger and scarier constellation of Scorpius (called Scorpio by the astrologers) on the 24th. Shows you what their astronomical knowledge is, doesn’t it?
Astronomy in Everyday Life
When I was teaching astronomy, naturally orbits, Newton, and Kepler and their laws on orbits would come up. But as part of that set of lessons is a traditional one from Newton—about shooting cannonballs horizontally at increasingly faster speeds. The ball would fall to the ground at farther distances. But…eventually, you had them going so fast that the ground was no longer horizontal but began to curve away underneath the cannonball. Shoot the ball fast enough and the gravitationally curved path of the ball matched the curve of the Earth’s surface and…bang!, you have a satellite. Welcome to orbital mechanics. Time to learn Kepler’s laws!
It is no different if you use a cannon ball….or a tennis ball….or any other horizontally (or not) projectile. And this spring I was so glad to see Kepler was inclined to help me out with a sports example:
Of course, NASA is quite skilled in orbital mechanics…..or so someone in a science humor feed thought…..
The Classroom Astronomer Newsletter - Inbox Magazine Issue 37 Highlights!
Cover Photo - Astronomy for Families
Welcome to Issue 37!
- Online Sky Events Calendar on The Galactic TimesPerceptions of Outreach- Results of a Survey
Astronomical Teachniques
- Not All Color Graphics Are Equal
- A Cosmic Partnership - A University-Library Cooperative for Caregivers and Children 4-7 Years Old (Cover StoryConnections to the Sky
- Pluto In CrisisSky Lessons -
- What Kinds of Questions Can You Get from Making Craters from Meteors?
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