Moon to Occult Aldebaran

Moon Occulting a Star

Astronomical alignments are special events, times when the motions of the Earth and the rest of the cosmos brings about a particularly interesting juxtaposition of objects in the sky. Today (Sunday 10 April) the waxing crescent Moon will align itself with the bright star Aldebaran, covering it completely for observers in various parts of North America. See this article from Sky & Telescope for a detailed overview of the cities and the exact timing for disappearance and reappearance of Aldebaran.

The Moon sweeps around the entire night sky and touches each constellation of the Zodiac every month, passing in front of hundreds of naked-eye visible stars during its journey. But it is very uncommon for the Moon to pass in front of the brightest stars in the night sky. Aldebaran is a 'first magnitude' star, one of only 22 stars that are at magnitude 1 or brighter (and only four of these are close enough to the Ecliptic to be ever occulted by the Moon: Aldebaran, Antares, Spica and Regulus)
. For that reason the covering and uncovering of a star like this is a dramatic event, worth taking a few minutes with binoculars or a telescope to watch the proper motion of the Moon as a vastly more distant star's light is interrupted by the surface on the edge of the Moon and the light twinkles and vanishes from view for an hour.

On the west coast, the event takes place in broad daylight, but that should not make it any less impressive. Disappearance is at 2:21 pm and reappearance at about 3:40 pm. Check the Sky & Telescope article for more precise timings from around North America.

Take part in "The Globe At Night" project - just look up at the sky tonight!

For the next week everyone is invited to participate in a global effort to measure light pollution and to learn about stars and the sky in your neighborhood, especially for those in big cities like San Francisco. The "Globe At Night" project invites people from around the world to take a few minutes in the next 7 days and look at one of the most beautiful constellations in the sky, Orion, and simply report how much of it you can see. It's easier than you think. And it's a great family project to show kids what you can see in the night sky.

The Globe At Night website provides all of the details, but in summary you compare what you see in your sky (your backyard, rooftop or any other convenient observing location) to a series of images on the Globe At Night website. By finding the image that best matches your view and reporting this on the website, you are helping to gather data from cities around the world on the relative light pollution in the sky. The constellation Orion contains stars of varying brightness, and depending upon the darkness of your skies, you will see more or less of these stars. The charts on the Globe At Night website show you Orion with differing "magnitudes" of stars, so for very light polluted cities you might only see the 1st and 2nd magnitude stars, whereas in darker skies you will see 3rd, 4th, or even 5th and 6th magnitude stars (the higher the number, the fainter the star).

Join the worldwide "Citizen Scientists" supporting this effort to increase awareness of the night sky, and take part. And bring along a friend. It's fun!

The Summer Triangle

One of the brightest objects in the nighttime sky each summer is called the Summer Triangle. Rather than being a single constellation, the Summer Triangle is an "asterism," a grouping of stars that make an interesting pattern but are not themselves a single constellation. The Summer Triangle is, as advertised, a very distinctive triangle of three very bright stars that form a 30-60 right triangle. The three bright stars are Vega, Deneb and Altair. With three stars at magnitude 0 or 1, the Summer Triangle shines through even light-polluted city skies.

If you have darker skies, the Summer Triangle is a quick guidepost to locating some of the most interesting objects you can see with binoculars or a telescope in the Milky Way. The image to the right is taken from the website of the Great Smoky Mountain Astronomical Society. I like their web images because they present a very easy-to-follow guide to the most interesting objects in the part of the Milky Way that passes through the Summer Triangle, including double stars, nebulae, star clusters and the patterns of the three constellations that include the three bright stars of the Summer Triangle: Lyra, Aquila and Cygnus. For another description of the same objects, try this page from the Royal Observatory in Greenwich.

Use your binoculars or a telescope - even if you are in a big city - and see how much of these constellations you can identify and how many of the interesting objects you can find lurking in their midst.