Happy Manhattanhenge

ManhattanSunset SmallToday (May 29) is Manhattenhenge. One of two days every year when sunrise and sunset are exactly aligned with the Manhattan (New York City, New York, USA) street grid. Just a fun fact. 

“What will future civilizations think of Manhattan Island when they dig it up and find a carefully laid out network of streets and avenues? Surely the grid would be presumed to have astronomical significance, just as we have found for the pre-historic circle of large vertical rocks known as Stonehenge, in the Salisbury Plain of England. For Stonehenge, the special day is the summer solstice, when the Sun rises in perfect alignment with several of the stones, signaling the change of season.” (from Sunset on the Manhattan Grid)

Summer’s almost here

I noticed yesterday that sunset is now occurring at 4:12pm. The day before it was 4:11pm. So sunset is getting later! Summer is almost here, right?

p.s. Before some smart-alec points it out, yes I know that sunrise is still getting later so the number of daylight hours are still shrinking.

It is left as an exercise to the reader to explain why the two events do not occur on the same day – in other words, sunset starts getting later several weeks before sunrise starts getting earlier. Note: the explanation is very complicated.

Tutorial on buying a telescope

Out of left (star) field. Here’s a succinct tutorial on buying a telescope that my friend Ben Gomes Casseres emailed me which I thought might be of general interest. You can see Ben’s own astronomy work here.

If you are thinking of buying a telescope (or giving one as a gift), Ben says:

The place to go to browse is http://www.oriontelescopes.com. They have advice on entry-level telescopes and such. Have Dick review what is available there and then let me know….I can help select among options. I am not sure what you can get for 500-1000, as there is a tendency for them to sell things for kids that are very cheap that are not worth it (poor optics, or flimsy mount, or just over-promising.)

As a general rule: Don’t skimp on the mount (heavy is good) or on the size of the “objective” (essentially the “width of the tube”…no less than 3” if a “refractor” type and no less than 6″ if a “reflector” type). At the same time, make it something easy to set up and take out of the box, or else it won’t be used. Don’t be fooled by “power” as most observing is done at 50x to 150x and anything higher is usually wasted. Leave some funds for books and atlas to help find things and see what is interesting to observe on a given night; and perhaps a subscription to “Sky and Telescope” (the standard in amateur astronomy) or “Astronomy” (more basic). The sites for these mags also have reviews that may be helpful.

You may find that a 3″ refractor (has a lens in front) on a nice mount might work; some are shorter than others (more $$) and offer wider fields of view. Or a “catadioptric” (lens in front + mirror in back and the optical path is folded on itself and so compressed in size) in the range of 6-8″. The most popular for many people is a 8″ Meade or Celestron catadioptric, which comes with mount and everything, but it is over 1k I would think. But check those out, as they are pretty good as one-size-fits-all instruments. Many other instruments are best for planets and moon but not for star fields and nebulas, or best for the latter but not the former.

A great pair of binoculars (7×50), such as Fujinon or other high quality, is also very nice and may be a good way to start. There are books on “roaming the sky with binoculars” (see Sky and Tel website) and in dark skies you can see a lot of wide-angle stuff. But that does not give views of moon and planets.

Hope this helps as guidance.