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    Early this week, watch for the Orionids
    Guy Ottewell in ASTRONOMY ESSENTIALS | October 20, 2019

    Charts and insights about this week’s Orionid meteor shower from astronomer Guy Ottewell.


    Here is the Orionid meteor stream (dotted line) striking Earth Sunday night. Guy Ottewell – who made this chart – lives in England, and he’s showing you Europe’s perspective tonight. The shower’s peak is likely Tuesday morning although Monday morning is good, too. The actual stream of particles in space – the meteor stream, debris left behind by Halley’s Comet – is millions of miles wide. People on all parts of Earth have a more or less equal chance of catching an Orionid meteor streaking across a dark night sky. Chart via Guy Ottewell’s blog.
    You may already have seen outlying meteors of the annual Orionid shower. They should reach a peak on the mornings of October 21 and 22, in the hours after midnight. Their zenithal hourly rate – the number that one alert person might count in an hour at the peak time, in perfect conditions and with the meteors coming from overhead – may be 25. You’ll be very lucky if you manage to count that many, especially as this year there is a last quarter moon in the sky at the same time.

    The radiant of a meteor shower is the point or small area among the stars from which the meteors seem to fly. They are particles of dusk or rock shed long ago from a comet – in this case, periodic comet 1P Halley.

    The particles emit light as they hit Earth’s atmosphere and burn up. Really, they are on parallel tracks, many miles apart, and can appear in any part of the sky. If you can trace one of these shining trails back to the Orion-Gemini constellations in our sky, it was an Orionid and not a sporadic meteor.

    In the picture above, Earth is seen from ecliptic north (the north pole of its orbit). The broad flat arrow shows its flight along its orbit in one minute, and the arrow on its equator shows its rotation in three hours. The actual stream of particles in space is millions of miles wide; the dotted line represents only those that happen to arrive from exactly overhead.

    For Europe at this time, just before dawn, the Orionid radiant and the moon are almost overhead. America is moving around toward midnight and toward a nearer view of the hemisphere of sky in which the meteors can appear.

    From all parts of Earth … the reason you may see more of these meteors after midnight, especially toward dawn, is that we are going to meet them: they are hitting Earth’s advancing front side, as shown in the illustration above. And that is because the orbit of their famous parent, Comet Halley, is retrograde – counter to the orbits of Earth and the other major planets.

    You can see that the inward track is across the October part of Earth’s orbit. That’s why we see Orionid meteors in October. And the outward track is across our orbit in May. And so we shall see a second Halley-derived shower, the Eta Aquariids, in May. The orbit does not exactly intersect Earth’s. We see meteors because the particles shed by a comet gradually diverge from its orbit, filling a vast tube of space.
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  2. #1242
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    What’s the source of the ice at the moon’s south pole?
    Paul Scott Anderson in SPACE | October 19, 2019

    A new study from Brown University suggests that different deposits of ice at the moon’s south pole not only originated from different sources, but also vary greatly in age.


    Deep and shadowed Shackleton Crater near the moon’s south pole is one location where scientists have found deposits of water ice. The ice has the potential to reveal insights about the moon’s history, and the history of our solar system. And it’s potentially useful to future moon explorers. Image via NASA/Goddard Space Flight Center/Leonard David’s Inside Outer Space.
    We tend to think of the moon as a dusty, bone-dry place, and for the most part, that is true. But the moon does have ice, in particular at its south pole, hidden in shadowed craters. Just how the ice got there has been a bit of a mystery, but now a new study suggests it may have various sources, both ancient and more recent.

    The new peer-reviewed findings were published in Icarus on September 30, 2019.

    This water ice has much value, both to scientists and future human explorers. According to Ariel Deutsch, lead author of the study and a graduate student at Brown University:

    The ages of these deposits can potentially tell us something about the origin of the ice, which helps us understand the sources and distribution of water in the inner solar system. For exploration purposes, we need to understand the lateral and vertical distributions of these deposits to figure out how best to access them. These distributions evolve with time, so having an idea of the age is important.

    The findings suggest that not only is some of the ice much older than the rest, but that there are probably different sources as well. Older ice could have come from water-bearing comets and asteroids or ancient volcanism. More recent ice deposits might be the result of pea-sized micrometeorites or implantation by solar wind.
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    A Mercury Transit Music Video from SDO
    Video Credit: NASA's Goddard Space Flight Center, Genna Duberstein; Music: Encompass by Mark Petrie



    What's that small black dot moving across the Sun? Mercury. Possibly the clearest view of Mercury crossing in front of the Sun in 2016 May was from Earth orbit. The Solar Dynamics Observatory obtained an uninterrupted vista recording it not only in optical light but also in bands of ultraviolet light. Featured here is a composite movie of the crossing set to music. Although the event might prove successful scientifically for better determining components of Mercury' ultra-thin atmosphere, the event surely proved successful culturally by involving people throughout the world in observing a rare astronomical phenomenon. Many spectacular images of this Mercury transit from around (and above) the globe were proudly displayed. The next transit of Mercury will take place in three weeks: on 2019 November 11.
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