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Star of the week: Alpha Centauri closest star system to our sun

Alpha Centauri A and B. The arrow points to the location of Proxima.

The Alpha Centauri system is said to be the closest star system to our sun. It’s a double, or triple, star system. The two main components are Alpha Centauri A and Alpha Centauri B. The third star, a red dwarf called Proxima Centauri, is thought to be about 4.22 light-years distant and is actually our sun’s closest neighbor among the stars.

Is it part of the Alpha Centauri system? The actual status of Proxima as a system member is unclear. It might simply be passing nearby but not part of the system, or it might be gravitationally bound.

Still, we often say – and many others say – that Alpha Centauri is the closest star to our solar system, with the assumption that Proxima is a true part of the Alpha Centauri system.

Young moon below Venus on May 19

The moon and planets are always found on or near the ecliptic - Earth's orbital plane projected onto the dome of sky.

Watch for the young moon and Venus on these evenings. You’ll always find them or near the ecliptic – the sun’s path on the dome of our sky.

Tonight – May 19, 2015 – people around the world will have a chance to catch the young moon beneath the blazing planet Venus after sunset. To view this very young moon, an extremely thin crescent up only briefly after sunset, you’ll want an unobstructed horizon in the sunset direction. Binoculars might come in handy for catching this little moon low in the bright twilight sky. Venus, meanwhile, will be blazing away, very bright and easy to see for a longer time after sunset.

New moon falls on May 18

Image credit: Moon Viewer

Image via Earth and Moon Viewer

Few, if any, people around the world can expect to see the moon before sunrise or after sunset today, on May 18, 2015. Today is the day of the new moon, the time of month when the moon and sun reside on the same side of Earth. Today, the moon pretty much rises with the sun at sunrise, crosses the sky with the sun during the daytime and sets with the sun at sunset.

Find the Omega Centauri star cluster


The sparkling blue-white star Spica can act as your guide to the Omega Centauri globular star cluster on these springtime nights. You can actually see this cluster with the unaided eye. Omega Centauri looks like a fairly faint (and possibly fuzzy) star. It’s a beautiful and very special star cluster, and Spica can help you find it.

Where is the Milky Way on May evenings?


Where is the starlit band of the Milky Way on these May evenings? That luminous band of stars crossing the dome of sky is nowhere to be seen during the evening hours in May. Why? The disk of our Milky Way galaxy is shaped like a pancake. On May evenings, the plane of the pancake-shaped galactic disk coincides with the plane of the horizon. Because the Milky Way rims the horizon in every direction in the evening in May, we can’t see this roadway of stars until later at night right now.

When is the next Blue Moon?

Beautiful image by our friend Jv Noriega. Thank you, Jv! Does a Blue Moon look blue like this? No. This photo was made using special filters to create the blue color.

A Blue Moon can be the second of two full moons in a month. Or it can be third of four full moons in a season. Next Blue Moon is the second full moon of July, 2015.

Look for the beautiful Northern Crown

Corona Borealis, the Northern Crown, as captured by Fred Espenak.  Used with permission.  Visit Fred Espenak's Portal to the Universe.

Corona Borealis, the Northern Crown, as captured by Fred Espenak. Used with permission.

Here is a constellation that’s easy to see on the sky’s dome, if your sky is dark enough. Corona Borealis – aka the Northern Crown – is exciting to find. It’s an almost-perfect semi-circle of stars. This beautiful pattern will adorn the evening sky from now until October.

Find a famous globular star cluster, M13


Photo of M13, the great Hercules globular star cluster, by John Giroux of Syracuse, New York. Thank you John!

M13 is a densely packed globular cluster of about 300,000 stars, more than 25,000 light-years from Earth in the constellation Hercules.

Arcturus cuts through galaxy’s disk

Arcturus is roughly 25 times greater in diameter than our sun. Arcturus / Antares/ sun size comparison from Wikimedia Commons.

Arcturus, a red giant, looks orange to the eye. It’s the brightest star on the northern half of Earth’s sky dome. Arcturus is especially noteworthy for its large proper motion, or sideways motion across our sky. Only Alpha Centauri – our sun’s nearest neighbor among the stars – has a higher proper motion among the first-magnitude, or bright, stars in the stellar neighborhood. What can the proper motion of Arcturus be telling us? Follow the links inside to learn more about this fascinating star.

Find the Keystone in Hercules


From mid-northern latitudes, you can easily find the brilliant star Vega in the eastern sky at dusk and nightfall. Vega acts as your guide star the Keystone – a pattern of four stars in the constellation Hercules. The Keystone, in turn, is your ticket to finding a famous globular star cluster in Hercules, otherwise known as Messier 13. And, before you search for Hercules and M13, be sure to look outside for the three planets in the west after sunset. You’ll find a chart showing Jupiter, Venus and Mercury inside this post.