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  1. #1221
    Moderator at Work ilan's Avatar
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    No, asteroid 2007 FT3 won’t hit Earth in October
    Eddie Irizarry and Deborah Byrd in SPACE | September 18, 2019

    Why is the internet so chock-full of stories about asteroids on a collision course with Earth? At this rate, we should have been obliterated many times over already. Here comes the newest scare story: asteroid 2007 FT3. No, it won’t hit us, either.


    This illustration shows the positions of Earth and asteroid 2007 FT3 on October 3, 2019. Note the space rock’s orbit (not the object itself) does come close to the orbit of the Earth. Image via NASA/JPL.
    Asteroid 2007 FT3 – a 1,115-foot (340-meter) space rock – is appearing in doomsday headlines suggesting the asteroid could hit our planet on October 3, 2019. Here’s an example: Deadly 1,100-Foot Asteroid Could Hit Earth In October, NASA Reveals. Sounds scary, right? But is it true? Is this asteroid really deadly? It’s only deadly if it kills something, and that’s not going to happen. Asteroid 2007 FT3 is not going to hit us. Of course, NASA knows that. What’s going on here? Why does the headline say NASA reveals?

    The truth is, asteroid 2007 FT3 is likely to pass Earth at such an extreme distance that even big professional telescopes at major observatories won’t be able to detect it this October. How far will it be at its closest distance? Preliminary estimates indicate asteroid 2007 FT3 will pass on October 3, 2019, at almost 360 times the Earth-moon distance. That’s many millions of miles, an enormous distance!

    Asteroid 2007 FT3 was discovered on March 20, 2007, from Mount Lemmon, in Arizona. It was observed only briefly – just 14 times over 1.2 days – and then became too faint to observe, disappearing back into the depths of space. Because it was observed for such a short time, there are uncertainties in its orbit. Those sorts of uncertainties for a newly observed, or briefly observed, asteroid are very, very normal and ordinary. They’re just part of the process.

    Because of the uncertainties, however, 2007 FT3 does appear in a “risk list” maintained by astronomers at the Center for Near Earth Object Studies (CNEOS) at NASA’s Jet Propulsion Laboratory in Pasadena, California. The Sentry Risk Table is part of a highly automated collision monitoring system that continually scans the most current asteroid catalog for possibilities of future impact with Earth over the next 100 years. Asteroid 2007 FT3 does appear on the current Sentry Risk Table (although objects are removed from this table as their orbits become better known).

    But being in a “risk table” doesn’t mean there’s actual risk. You’ll see that 2007 FT3 has an extremely low chance of impacting Earth in October:

    0.00015% chance of Earth impact
    1 in 670,000 odds of impact
    99.99985% chance the asteroid will miss the Earth

    Let’s linger on the Sentry Risk Table a little longer. CNEOS, which maintains this table, explains on its website:

    When interpreting Sentry pages, where information on known potential NEA [Near-Earth Asteroid] impacts is posted, one must bear in mind that an Earth collision by a sizable NEA is a very low probability event. Objects normally appear on the Risk Page because their orbits can bring them close to the Earth’s orbit and the limited number of available observations do not yet allow their trajectories to be well-enough defined. In such cases, there may be a wide range of possible future paths that can be fit to the existing observations, sometimes including a few that can intersect the Earth.
    Whenever a newly discovered NEA is posted on the Sentry Impact Risk Page, by far the most likely outcome is that the object will eventually be removed as new observations become available, the object’s orbit is improved, and its future motion is more tightly constrained. As a result, several new NEAs each month may be listed on the Sentry Impact Risk page, only to be removed shortly afterwards. This is a normal process, completely expected. The removal of an object from the Impact Risk page does not indicate that the object’s risk was evaluated mistakenly: the risk was real until additional observations showed that it was not.

    And so on and so on. We encourage you to read all of this page if you want to understand the Sentry system.

    Now let’s look at another important tool for understanding Near-Earth Asteroids (NEAs): the Torino Scale. It was created by astronomer Richard P. Binzel of MIT in 1995 and presented at a United Nations conference that year. CNEOS described the Torino Scale this way:

    The Torino Scale, adopted by the [International Astronomical Union] in 1999, is a tool for categorizing potential Earth impact events. An integer scale ranging from 0 to 10 with associated color coding, it is intended primarily to facilitate public communication by the asteroid impact hazard monitoring community. The scale captures the likelihood and consequences of a potential impact event, but does not consider the time remaining until the potential impact. More extraordinary events are indicated by a higher Torino Scale value.

    Asteroid 2007 FT3 has a Torino Scale ranking of 0, which indicates:

    The likelihood of a collision is zero, or is so low as to be effectively zero.

    Even with the poorly constrained orbit or limited data, NASA scientists estimate that on October 3, 2019, asteroid 2007 FT3 should pass at some 86 million miles (138 million km) from Earth.

    2007 FT3 should be a little “closer” to Earth on October 11, 2068. During that “closer” approach, the space rock should be passing at more than 15 million miles (24.5 million km), or about 64 times the Earth-moon distance. That’s still a huge distance.

    2007 FT3 is categorized as an Apollo-type asteroid. It takes 1.2 years (438 days) to complete an orbit around the Sun. Its orbit – not the object itself – does come close to the orbit of the Earth, and it is therefore considered a potentially hazardous asteroid, by CNEOS:

    Potentially Hazardous Asteroids (PHAs) are currently defined based on parameters that measure the asteroid’s potential to make threatening close approaches to the Earth. Specifically, all asteroids with a minimum orbit intersection distance (MOID) of 0.05 au [astronomical units] or less and an absolute magnitude (H) of 22.0 or less are considered PHAs.

    Do you see what’s going on here? In recent decades, astronomers have realized the potential for asteroids to strike Earth. That is a very real potential. The world as a whole has recognized that it’s important for a planet with 7.6 billion humans to understand the potential threat of asteroids, and to track asteroids, and even to discuss what we might do if we did learn an asteroid was heading our way. Hopefully, we would learn this some years before it happened, and not days before.

    But all of this formalization of a potential threat – nomenclature, lists, acronyms – has also created a potential to create misunderstandings and fear. And, we all know, on the internet fear means clicks, and clicks mean $$.

    Meanwhile, the asteroids are just out there, as they’ve been for billions of years, pursuing their orbits around the sun. If asteroid 2007 FT3 is re-observed in late September or early October 2019, the new observations might let astronomers better refine its orbit. Then, perhaps it’ll be removed from the Sentry Risk Table.

    In the meantime, don’t worry. What you’re seeing here is just astronomy in action, and, in particular, the branch of astronomy that aims to keep us safe from asteroids. And the preliminary data – based on these astronomers’ best-possible observations and most careful orbit calculations – clearly indicate that this particular asteroid, 2007 FT3, poses no risk to our planet.
    Last edited by ilan; 09-21-2019 at 04:05 PM.
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  2. #1222
    Moderator at Work ilan's Avatar
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    An astronomer contemplates the equinox
    Guy Ottewell in ASTRONOMY ESSENTIALS | HUMAN WORLD | September 21, 2019

    You can think of the equinox not as a whole day, but as a point along Earth’s orbit. Want to understand that better? Guy Ottewell offers some insights.


    This view is about 7 hours before the instant of the September 23 equinox. Image via Guy Ottewell’s blog.
    The September equinox falls on Monday, September 23, 2019, at about 8 o’clock by Universal Time. That is after sunrise for Europe, but by American clocks, it’s nearer to the midnight between Sunday and Monday. So the good time to contemplate equinoxes is on Sunday evening.

    The chart at top shows the view only about seven hours before the instant of the equinox (September 23, 2019 at 07:50 UTC).

    The sun is arriving at one of the two places where the ecliptic (sun’s path on our sky’s dome) crosses the celestial equator (imaginary line above Earth’s equartor). In other words, the sun is moving into the southern celestial hemisphere. At the opposite crossroads in the sky – 180 degrees away on the sky’s dome – we show an imaginary anti-sun, toward which the shadow of our Earth points.

    And halfway between them is the antapex of Earth’s way, the point away from which we are moving in our orbit.

    Near this are Jupiter and Saturn, because at this time we are rushing away from them in orbit around the sun. Earth passed between the sun and each of these planets in the summer. Jupiter appeared exactly 90 degrees from the sun (east quadrature) on September 8, and the antapex will reach Saturn on October 7.


    This 3-dimensional picture shows the planets’ orbits and their paths in the month of September, with sight-lines from Earth to the sun and planets at September 23, 2019. Image via Guy Ottewell’s blog.
    The three-dimensional picture shows the heliocentric view for September 2019, with sight-lines from Earth to the sun and planets at September 23. The viewpoint is six astronomical units (AU, or sun-Earth distances) from the sun, at a latitude of 15 degrees north of the ecliptic (Earth-sun) plane and longitude of 45 degrees from the vernal equinox direction (the “zero” point of the sky). We see the sun in that direction at the March equinox; the sun sees us in that direction at the September equinox.

    I was out this morning at my cliff-top “dawn point” in good time to see the sunrise. After that inevitable building of suspense, the sun flashed out from the steep face of Golden Cap. It was 7:05 a.m., would have been I think 12 minutes earlier down on the geometrical horizon. I had forgotten to take in my bicycle pannier the means to make a picture, and tomorrow the clear September weather (which has allowed me some swims in the sea) may be over, so for an equinox sunrise picture I’ve had to pull the sun up into a pre-dawn one I made in a past year.
    Last edited by ilan; Yesterday at 12:53 PM.
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