Sunday, December 27, 2009

upcoming eclipses

Thanks to Nurit and Asher for the notice and info.

Get ready for not one, but 2 eclipses!

This Thursday night, Dec 31, we will have a very slight lunar eclipse. The view will be about the same from anywhere on this half of the globe.Only about 7% of the oon will enter the Earth's shadow. The casual observer may not notice anything, but it's more pronounced through binoculars or a telescope.

Lunar eclipse Thursday,Dec 31
starts -  20:53 IST
ends  -  21:52 IST

Look for the full moon high in the eastern sky. The shadow will be most pronounced at mid-eclipse, around 9:25pm on lower right side of the moon.

January 31st will thus be a momentous date!  Not only will it mark the end of 2009, but the lunar eclipse will also fall on a "blue  moon," which in popular usage (there are alternate definitions) is the second full moon in a calendar month (the first was Dec. 2).

Monday, December 21, 2009

Happy winter solstice

Today at 19:47 Israel time, the Sun will appear to stop (thus "Sol stat" from the Latin) on it yearly journey to the south and begin to turn around. This has the effect of making today the shortest day of the year, with the sun only up10 hours and 5 minutes.

Although this is the official 1st day of winter in the norther hemisphere (also known as midwinter day) the days will actually start to get longer starting tomorrow. However, don't put away your winter clothes yet. Due to the large thermal mass of water on the globe (75%) it will continue to get colder through Jan.

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Saturday, December 19, 2009

Choosing Your First Telescope


As a followup to my previous post Buying your 1st Telescope,  here is more from a recent article in  Sky & Telescope


Choosing Your First Telescope

Every year millions of people buy a telescope, but few know what to look for when making their purchase.

by J. Kelly Beatty

With a little guidance, you can pick a high-quality telescope that can last a lifetime. Click on the image to see seven important tips when buying a telescope.
S&T: Craig Michael Utter
Here's a quick guide to help you make sense of the hundreds of telescope models available today. Armed with these few basics, you'll have a good idea what to look for (and what to avoid) when scouring the marketplace for your new scope. If you still have questions or need more details, check out our extended help guide.Many (arguably most) good starter scopes cost $400 or more, but some superb choices are available for under $250. For some specific recommendations, read our review of Lost-Cost Starter Scopes. But read this article first, so you'll understand the terminology in that review.
The telescope you want has two essentials: high-quality optics and a steady, smoothly working mount. And all other things being equal, big scopes show more and are easier to use than small ones, as we'll see below. But don't overlook portability and convenience — the best scope for you is the one you'll actually use.
The most important characteristic of a telescope is its aperture — the diameter of its light-gathering lens or mirror, often called the objective. Look for the telescope's specifications near its focuser, at the front of the tube, or on the box. The aperture's diameter (D) will be expressed either in millimeters or, less commonly, in inches (1 inch equals 25.4 mm). As a rule of thumb, your telescope should have at least 2.8 inches (70 mm) aperture — and preferably more.

Dobsonian telescopes provide lots of aperture at relatively low cost.
S&T: Craig Michael Utter
A larger aperture lets you see fainter objects and finer detail than a smaller one can. But a good small scope can still show you plenty — especially if you live far from city lights. For example, you can spot dozens of galaxies beyond our own Milky Way through a scope with an aperture of 80 mm (3.1 inches) from a dark location. But you'd probably need a 6- or 8-inch telescope like the one shown at right to see those same galaxies from a typical suburban backyard. And regardless of how bright or dark your skies are, the view through a telescope with plenty of aperture is more spectacular than the view of the same object through a smaller scope.Avoid telescopes that are advertised by their magnification — especially implausibly high powers like 600×. For most purposes, a telescope's maximum useful magnification is 50 times its aperture in inches (or twice its aperture in millimeters) . So you'd need a 12-inch scope to get a decent image at 600× And even then, you'd need to wait for a night when the observing conditions are perfect.
Telescope Types
You'll encounter three basic telescope designs.Telescope types
Refractors have a lens at the front of the tube — it's the type you're probably most familiar with. While generally low maintenance, they quickly get expensive as the aperture increases.
Reflectors gather light using a mirror at the rear of the main tube. For a given aperture, these are generally the least expensive type, but you'll need to adjust the optical alignment periodically — especially if you bump it around a lot.
Compound (or catadioptric) telescopes, which use a combination of lenses and mirrors, offer compact tubes and relatively light weight; two popular designs are called Schmidt-Cassegrains and Maksutov-Cassegrains.
The objective's focal length (F or FL) is the key to determining the telescope's magnification ("power"). This is simply the objective's focal length divided by that of the eyepiece, which you'll find on its barrel. For example, if a telescope has a focal length of 500 mm and a 25-mm eyepiece, the magnification is 500/25, or 20x. Most telescopes come supplied with one or two eyepieces; you change the magnification by switching eyepieces with different focal lengths.
Telescope Mounts
 Telescope mounts
Your telescope will need something sturdy to support it. Many telescopes come conveniently packaged with tripods or mounts, though the tubes of smaller scopes often just have a mounting block that allows them to be attached to a standard photo tripod with a single screw. (Caution: A tripod that's good enough for taking your family snapshots may not be steady enough for astronomy.) Mounts designed specifically for telescopes usually forgo the single-screw attachment blocks in favor of larger, more robust rings or plates.
On some mounts the scope swings left and right, up and down, just as it would on a photo tripod; these are known as altitude-azimuth (or simply alt-az) mounts. Many reflectors come on an elegantly simple wooden platform, known as a Dobsonian, that's a variation of the alt-az mount. A more involved mechanism, designed to track the motion of the stars by turning on a single axis, is termed an equatorial mount. These tend to be larger and heavier than alt-az designs; to use an equatorial mount properly you'll also need to align it to Polaris, the North Star.
Some telescopes come with small motors to move them around the sky with the push of a keypad button. In the more advanced models of this type, often called "Go To" telescopes, a small computer is built into the hand control. Once you've entered the current date, time, and your location, the scope can point itself to, and track, thousands of celestial objects. Some "Go To"s let you choose a guided tour of the best celestial showpieces, complete with a digital readout describing what's known about each object.
But Go To scopes aren't for everyone — the setup process may be confusing if you don't know how to find the bright alignment stars in the sky. And lower-priced Go To models come with smaller apertures than similarly priced, entry-level scopes that have no electronics.
Remember …
A telescope can literally open your eyes to a universe of celestial delights. With a little care in selecting the right one, you'll be ready for a lifetime of exploring the night sky!


Tuesday, December 15, 2009

It was a great Meteor Shower

Well guys, the Geminids put on a great show!

I went down with 4 of my kids the Mahktesh Hakatan to camp out. We where met by Gadi and some of his kids and a guest, plus one of the new members to our list Yanki.

It was a great night. Unlike the forecast it was not too cold. Thanks to the Mahktesh, there was no wind, and the cold front did not roll in as expected, so it stayed clear all night.

I am too tired for a full report now, but we saw hundreds of meteors. After we cooked our hot dogs and set up our tents me and the kids layed down outside and counted at least 100 in the course of about an hour. By about 1am I nodded of inside my sleeping tent, but I think Gadi and the other guys where up most of the night. Hopefully they will add their reports soon.

You can see our campsite and group photo here:

The Geminids have been getting stronger for years now. According to Nasa it is expected to continue to improve. So be ready for next year.

For more reports and photos see Space Weather

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Sunday, December 13, 2009

Reminder Geminid Meteor shower tonight

Hi ya'll,

Mak sure to be on the lookout for meteors tonight.

APOD: 2009 December 12 - Geminid Meteor over Monument Valley

See Explanation.  Clicking on the picture will download  the highest resolution version available.

 I plan to camp out with the kids  in in Makhtesh hakatan tonight. Hopefully we'll find some clear skies down there.
If you want to join us, drop me a line.

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Sunday, December 6, 2009

Buying your 1st Telescope

Question: What sort of telescope would you recommend for a beginning astronomer (me) who has a child who is very interested in space?  (She is only 6, so of course interests might fade, but I would like to encourage it while I can).  I would like something decent enough that we can find and see interesting things, but hopefully not too expensive...
Also, would it be recommend to buy one here in Israel, or have it shipped from the states?  (Or even "manually imported" if I can find someone to schlep it...).  Is there a local second-hand telescope market here?


I often get asked that question. I need to work on a more complete  FAQ but here is a quick draft.

First of all, the best type of beginner scope is a pair of binoculars. Any old pair you have laying around the house will give you a better view than your eyes. If you don't already have a pair, you should invest in a quality pair 7x35 or  10x50 pair. (More on what those numbers mean in a future post) [or see the link below] Something like this model  should cost between $50-$100.  

When you are ready for a telescope I highly recommend a 4 and 1/2  inch Dobsonian model. Something like this: Orion SkyQuest XT4.5 Classic Dobsonian Telescope
Orion sells a great Skyquest model for a little more than $200. You'll note that this is a reflector type telescope, not the classic refraction you usually think of. More on the differences in a later post, but you get a lot more for your money with a Dobsonian reflector than any other model.

The 4.5 inch is big enough to get some very nice view of planets and clusters, but it is not too big that it  is a pain to schlep around. It also also very easy for kids (and adults) to work and aim (which is not trivial).

You can bring these  back pretty easily on a plane from the US. I know lots of people who have done it. It is delivered in 2 pieces. The unassembled base, which comes in a nice flat box you can check, and the tube, which you can carry on, and fits nicely in the overhead bin.

You can of course buy it in Israel, but since there is about one store in the country, it costs about twice as much. The Cosmos store is in Ramat Gan. The number is 03-6724303.

If you really have a small budget and are willing to invest in a scope you will probably outgrow quickly, there is a new quality scope the Celestron FirstScope. It is only 3 inches but a quality piece.

For more see also at Sky and Telescope
And some more links at Astronomy Magazine:
    Unlike the advice given in the video above, I do not  recommend a "GoTo" scope for beginners. A good Goto costs way too much and a cheap one will only frustrate you and take much of the fun and education out of the hobby.

    For the 2nd hand market, you can check out the Hebrew Nana astro forum.


    Thursday, December 3, 2009

    Busy month for planets

    December will be action packed with planets this year.

    At the beginning of the evening now, Jupiter is still the star of the show, but each night it is getting lower and lower into the haze in the southwest setting by 10pm.

    Have you all spied Mercury? If not this is a great month to catch this elusive planet. It is now visible in the southwest, right after sunset at magnitude -0.5. It will be at its max brightness of -.06 by next Friday. A week later on the 18th it will make a pretty pairing with the new moon just in time for Rosh Chodesh. A week later it will begin its quick plunge back toward the sun disappearing by years end.

    Mars is already magnitude 0 and still brightening and getting larger. By 10pm it is already up and getting higher each night. In a small scope you should be able to see the norther ice cap!

    You have to be up pretty late to catch Saturn as it only rises around 1:30am. But by by the end of the month it will be up by 11:30. It is recovering from the ring crossing earlier this year and they are now getting wider again.

    Venus, is still visible in the dawn sky, but is getting closer and closer to the sun till it disapears by month end. It will reappear in the evening sky, after a hiatus of about a year, by the end of January just in time to switch off with Jupiter as the evening star.

    Have any of you ever bagged Neptune? I don't think I have even ever tried, but if you have a decent scope this month is the month to try. It is actually very close to Jupiter, and they will be onlu .6 degrees apart (about the size of the (Moon) for a few days around the 21st.

    Oh and by the way, this month we also get a Blue Moon. This is when we have 2 full moons in one calendar month. The first one was last night, and the 2nd one will be on the last day of the month (and year) It of course has no astronomical significants, but you get to use the "once in a blue moon" adage.

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