The University of Arizona
Mt. Lemmon SkyCenter

The Captivating Cosmos

December 25, 2010


Almach: A star system that is the 3rd brightest star in the constellation of Andromeda. It is considered by amateur astronomers to be a beautiful double star with a striking contrast of color. When viewed in a small telescope, or the 24" RC telescope at the SkyCenter, it appears to be a bright yellow star (Almach A) next to a dimmer greenish-blue star (Almach B), separated by approximately 10 arcseconds. Almach A is approximately 1,500 times brighter than our own Sun. It was later discovered that the dimmer greenish-blue star is in fact a triple star system. What appears as a single star to the naked eye is thus a quadruple star system, approximately 350 light-years from Earth.

Double Cluster

The Double Cluster is a naked-eye open cluster pair consisting of NGC 884 and 869, which are visibly close together in the constellation of Perseus. NGC 884 and NGC 869 are 7600 and 6800 light-years away, respectively, so they are close to one another. They are relatively young clusters, with NGC 869 being 6 million years old and NGC 884 at 3 million years. By comparison, the Pleiades Cluster, M45, has an estimated age ranging from 75 million years to 150 million years.


Messier 31, the Great Andromeda Galaxy, thanks to Edwin Hubble and the 100" Hooker telescope on Mt. Wilson, played a pivotal role in the science of astronomy. Until Hubble discovered Cepheid variable stars in 1923 in what was then known as the Great Andromeda Nebula, no one seriously considered that this naked eye smudge of glowing light in the constellation Andromeda was another galaxy very similar to our own. A classic spiral galaxy, M31 is our closest neighbor galaxy, at only 2.5 million light-years away.


The third largest member of the Local Group of galaxies (only the Milky Way and Andromeda are larger), Messier 33, the Triangulum Galaxy, approximately 3 million light-years away in the constellation Triangulum, is a lovely spiral that is actually a naked eye object under excellent conditions. A delight in binoculars, it is a WOW in a large-aperture telescope.

NGC 253

The largest member of the Sculptor Group of galaxies (the closest group to our own Local Group), named for the constellation in which they reside, NGC 253 is also the brightest. Called a starburst galaxy due to the intense star formation going on in its core, it is a classic spiral tilted only slightly to our line of sight. At a distance of approximately 13 million light-years, much of the brilliance of this large galaxy is muted by the vast amounts of dust visible everywhere in its spiral arms and central hub. It is a favorite of amateur astronomers and astroimagers for obvious reasons.

Binary star

Among the loveliest objects in the sky, a binary star system (two stars that are physically close and gravitationally bound to each other) with distinctly different colored stars, such as Iota Cancri (in the constellation Cancer) and Albireo (the "head" of Cygnus the Swan), can dazzle the eye with their beauty. Albireo's brighter amber/yellow star is actually a binary itself, while its blue/green companion seems to be solitary. It's not even known if the two major stars are gravitationally related to each other; if they are, a complete orbit would take over 100,000 years. Other yellow/blue binary systems often shown in the program include Izar (in Bootes) and Cor Caroli (Alpha Canum Venaticorum).

Carbon star

V Hydrae, R Leporis, and Hind's Crimson Star, all carbon stars, rank among the reddest stars in the sky. A carbon star is a late-type giant star similar to a red giant (or occasionally to a red dwarf) whose cool atmosphere contains more carbon than oxygen; the two elements combine in the upper layers of the star forming carbon monoxide, which consumes all the oxygen in the atmosphere. The excess carbon is then free to form other carbon molecules, giving the star a 'sooty' atmosphere. The concentration of carbon soot and interior radiation pressure builds until the outer shell of carbon is blown off the star. The process repeats and makes the star's brightness vary in days or weeks.

Daytime view of a star

Finding a star or planet through a telescope while it's still daylight used to be tricky and highly dependent on luck, but it has been rendered a "piece o' cake" with go-to telescopes and the software that directs them. Still, it is a thrill to see Sirius (in Canis Major), Regulus (in Leo), or Arcturus (in Bootes), or any of the other bright stars while our closest star (the Sun) is still flooding the sky with its light. Somehow one doesn't think of the stars being "there" during the daytime, but they certainly are, and a good telescope will show them to you: brilliant points of light against a dazzlingly blue sky.


The International Space Station (ISS) and Hubble Space Telescope (HST) orbit the Earth in precise paths that cross over parts of the U.S. and the rest of the world at predictable times. Although it's conceivable that you might be able to see one during daylight, if you knew exactly where and when to look, it is much more likely that they will be sighted at night, when sunlight reflects off their shiny surfaces and makes them appear as swiftly-moving stars. provides the information necessary to find out if you will be able to see these and other satellites from your location (a dark sky site is preferable as neither the ISS nor HST is particularly bright and would probably be lost in the glare of city light pollution.)


Few cosmic vistas excite the imagination like the Orion Nebula. Also known as M42, the nebula's glowing gas surrounds hot young stars at the edge of an immense interstellar molecular cloud only 1,500 light-years away.The Orion Nebula offers one of the best opportunities to study how stars are born partly because it is the nearest large star-forming region, but also because the nebula's energetic stars have blown away obscuring gas and dust clouds that would otherwise block our view - providing an intimate look at a range of ongoing stages of starbirth and evolution.

NGC 7662

Popularly known as the Blue Snowball Nebula, this planetary nebula, NGC 7662, in the constellation Andromeda is a delight to see through a good telescope: blue-green in color with some visible structure in the nebulosity, and a bluish-white central star. At a distance of approximately 1,800 light-years, this is a very popular deep sky object.


Jupiter, a gas-giant planet fifth out from the Sun, is the largest in our solar system, and, it is now believed, one of the reasons why life has flourished on Earth. Had Jupiter not been around, sweeping, vacuuming, and ejecting objects from the orbits of the inner planets, Earth might never have had the relatively-unbombarded span of years necessary in which to evolve complex living organisms. It was toward Jupiter that Galileo Galilei turned his newly-constructed telescope in 1609, discovering a system of four moons orbiting the planet. This was contrary to "known" doctrine at the time and led to the science of modern astronomy, as well as to Galileo's imprisonment. Jupiter has a ring system, aurorae, massive lightning storms, and a multitude of moons. The Great Red Spot is a "storm" that has been visible and studied for over 300 years; if you're very lucky, it will be visible through the 24" on the night you observe the planet.


Named after the Roman god of the sea, possibly due to its distinctly blue color, Neptune is the eighth planet from the Sun and one of four planets with a ring system. Discovered in 1846, its existence was deduced by mathmatics rather than by actual observation: the orbit of Uranus displayed perturbations which led astronomers of the time to suspect the presence of an as yet unknown planet. It was found within a degree of its predicted position! Neptune is 17 times the mass of Earth and orbits at 30 times the Earth's distance from the Sun, completing one orbit in about 165 years. The outermost of the "gas giant" planets, Neptune's atmosphere contains mostly hydrogen and helium along with traces of hydrocarbons such as ammonia and methane. It has a faint, incomplete ring system which was verified in 1989 when Voyager 2 made the only spacecraft visit so far.


Our closest star, the Sun, along with every other visible object in the sky, was once thought to circle the Earth, since most observations supported this hypothesis. However, over centuries, scientists dissatisfied with discrepancies in the orbits of the known planets discovered step by step that the Earth was simply a member of the group of planets and other objects which orbit the Sun. At almost 93 million miles away (one Astronomical Unit, or AU), the Sun, a "main sequence" star, provides the energy, in the form of sunlight, which supports the majority of life on Earth. Through the process of nuclear fusion, the Sun constantly converts hydrogen to helium and other elements. It has been doing this for approximately 4.5 billion years and will continue to do so for another 5+ billion years.


Messier 15 (NGC 7078) is a globular cluster in the constellation of Pegasus, discovered in 1746 by Jean-Dominique Maraldi. At an estimated 13.2 billion years old, it is one of the oldest known globular clusters. M15 is about 33,600 light-years form Earth and is one of the most densely-packed globulars known in our Milky Way Galaxy. Viewing M15 through a small telescope, the cluster appears as a fuzzy star, but in the 24" RC telescope at the SkyCenter, individual stars appear, as does the densely packed central core.


Messier 45, the Pleiades, is a striking open star cluster which formed 75 to 150 million years ago. It is among the nearest star clusters to Earth and is visible in the evening during the late fall and winter months. The Pleiades are one of the most conspicuous clusters in the sky. Most people can see 6 or 7 members with their unaided eyes. However, a view through binoculars reveals the myriad beauty of this cluster of young stars, which actually contains over 1,000 confirmed members. The Pleiades also carry the name "Seven Sisters", which, according to Greek mythology, are seven daughters and their parents. Their Japanese name is "Subaru", which was taken to brand the car of same name. The Pleiades do not comprise the "Little Dipper" which is associated with the North Star, Polaris!

Thank you for joining us this evening. Please come again to experience more of our beautiful Universe!

You can view this handout online at

Other programs:

Astronomer Nights: Use the telescope all nignt long for one or two nights!
Discovery Days: Enjoy the sky island nature of Mt. Lemmon and escape the heat!
Mirror Lab Tours: See where the largest telescope mirrors in the world are made.
Workshops: Hosted on-site for an unforgettable experience.

See our website for details:

Suggested books and websites:
Brian Greene, The Fabric of the Cosmos                   Satellites:
Lynch and Livingston, Color and Light in Nature          Weather imagery:
Peterson Field Guide to the Stars and Planets            Clear Sky Chart:
Michael Bakich:  The Cambridge Encyclopedia of Amateur Astronomy

Other UA College of Science Outreach Facilities
Steward Observatory Mirror Lab Biosphere 2 The Laboratory of Tree Ring Research

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