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Monday, November 27, 2017

Geminids Meteor Shower 2017 in Israel

Did you get skunked by the Leonids meteor shower last month? Me, too. The run up to the peak was disappointing with only a handful of meteors seen in the early evening up to the day before the peak. The peak occurred on Shabbat when we don't go out, so we don't know what it was like, but the denouement the following days was also sparse with meteors.

You get to try again with the Geminids meteor shower which peaks this year during Chanukah on the night of December 13 and December 14. The actual peak itself is forecast to fall at 8:30AM, Israel Standard Time, on the morning of December 14, in other words in daylight. But the previous night of the 13th and the night of the 14th itself should still be very good, especially since this year there is no bright moon in the sky to interfere with the shower.

The Geminids is one of the most reliable showers of the year with the peak showing up to 120 meteors per hour. It is also a good shower for children since the radiant of the shower, the point in the sky from which the meteors appear to emanate, is already high overhead early on winter evenings, starting around 9:00 to 10:00PM. The radiant is in the constellation Gemini from which the shower, like all meteor showers, takes its name. It is already high up early in the evening. All meteor showers show best after midnight, since then the earth is turning in the direction of its orbit around the sun, increasing the entry velocity of the meteoroid particles into the earth's atmosphere. But it isn't necessary to wait until after midnight to see lots of meteors if the shower performs as expected.

The radiant of the Geminids meteor shower lies in the constellation Gemini. It lies near the bright star Castor in Gemini. It isn't necessary to look at teh radiant when observing but since meteors come from all sides of it, one generally sees more meteors when lookin in the direction of the radiant. For the Geminids look northeast before midnight. After that, follow the constellation as it crosses the sky in the early hours of the evening.

Meteors are bright streaks of light made by tiny particles of dust and rock from comets or asteroids. As these particles fall to earth they burn up from the heat of friction in the earth's atmosphere. Most of these particles are the size of a grain of sand, so  obviously we are seeing the brilliant light they make as they incinerate themselves in the earth's dense atmosphere, not the particle itself. So meteors are very much local phenomena, becoming visible some 75-150 miles in the air above us.

Although meteors can be seen every night throughout the year, a meteor shower occurs when the earth passes through the path of an ancient comet or asteroid as it orbits the sun. Then all of the debris of the comet or asteroid falls to earth at roughly the same time, creating showers of particles in our atmosphere. Meteor showers are whole sky phenomena and not only is optical  aid unnecessary it is detrimental to viewing the shower. Your unaided vision gives you the widest field of view of the sky.

A meteor shower occurs when the earth crosses the path of an ancient comet or asteroid and the debris from the object rains down on the earth simultaneously.
The Geminids meteor shower originates not from a comet but from  3200 Phaethon, an asteroid discovered in 1983 that circles the sun every 3.3 years. In fact, recent observations suggest that Phaethon might be a "rock comet" that sheds particles when its surface heats up roughly to 1,300 degrees F (700 degrees C) at each perihelion.

We will have star tours every night of Chanukah, including of course the peak shower nights of December 13 and 14. Come on out and enjoy the show.

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Tuesday, November 14, 2017

Leonids Meteor Shower 2017 in Israel

The Leonids Meteor  Shower peaks on the night of  November 17 and early morning November 18. The night of November 16 should also be good. The peak number of meteors visible at maximum, the Zenith Hourly Rate (ZHR), is 20 meteors per hour. This is when the radiant of the shower, in the constellation Leo, is overhead. The radiant is the point in the sky where the meteors seem to emanate from when a line is drawn back from their path of travel in the sky. These lines converge at a point in the sky called the radiant. For this meteor shower it is located in the constellation Leo, hence the name of the shower.

The ZHR is a predicted maximum. Most meteors during a shower are quite dim, so very few people every see the theoretical maximum for the shower. Even far more intense showers than the Leonids frequently show far fewer numbers than the peak rate, especially if you miss the exact maximum or do not have fully dark skies. There is no moon in the sky during the peak of the Leonids this year, so it should put on a nice show if you can get to a dark location.

Meteors are bits of rock from comets or asteroids that fall to earth at very high speeds and burn up in the earth's atmosphere. Most are quite tiny, about the size of a grain of sand. We see the bright light they make as they burn up from the heat of friction in the earth's atmosphere, not the body itself. The comet from which the Leonids result is Comet Tempel-Tuttle.

We will be having a star tour on Thursday night, November 16, 2017 at 9:30pm. We don't go out on Shabbat and won't be having a star tour on Saturday night November 18. November 19 and 20 should also have some shower activity, but it's difficult to tell how intense it will be. If you'd like to join us that would be delightful.

Status Update:
As of the evening of November 16, nothing major to report. Only a handful of meteors seen on star tours up through and including Thursday night, November 16.

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The radiant of the Leonids meteor shower lies within the boundary of the constellation Leo. You don't have to be looking directly at it to see shower members. They can appear anywhere in the sky. But since Leo will be rising in the East for much of the peak night, it's best to lie on the ground facing eastward. No optical aid is required. Meteor showers are entirely naked eye events. This is the sky at about 5:30am on November 18, 2017. It will look substantially the same the entire week of November 12, except for the moon which will get smaller and smaller and closer and closer to the horizon as the week progresses. It is new on November 19.

If you stay up until dawn the week of November 12 you will be treated to the sight of Venus and Jupiter in conjunction with each other and the waning crescent moon getting ever closer to them morning by morning. This is the sky at 5:31am on November 17, just before dawn, which is when Jupiter, Venus and the moon will start to become visible above the eastern horizon. What a treat  to see them all together with the peak of the Leonids meteor shower!

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Sunday, November 12, 2017

Venus and Jupiter Meet in the Morning Sky November 13, 2017

You may have read this somewhat misleading post on Facebook about Jupiter and Venus “passing” each other in the morning sky on November 13.

Another misleading Internet astronomy post. You will not see Venus and Jupiter move as you watch them. They are, however, close together in the sky all week long, not just Monday morning. You will also see the red planet Mars above them with the crescent moon hanging above the entire tableau. Look East/Southeast before dawn. The attached image shows where to look and what you will see. You will need a very clear Eastern horizon as Jupiter and Venus are low in the sky and appear just before sunrise. The diagram below is at 5:31am on Monday morning. The moon will continue to move closer to the pair throughout the week and will be closest on Friday morning when the trio will form a spectacular sight at 5:30am.

Jupiter and Venus are in conjunction on the morning of November 13, 2017. They continue to be a close pair in the early dawn sky all week long.

The crescent moon accompanies Venus and Jupiter later the week of November 13.


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