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Saturn - Saturn is a gas giant and the sixth furthest planet from our Sun. It is primarily

composed of hydrogen and helium. Its about 95 times the mass of Earth and ~ 9 times the

diameter (depending on equatorial or polar diameter). The reason the rings of Saturn are sovisible when compared to Jupiter, Uranus, and Neptune is they are mostly composed of icy

fragments as opposed to rocky ones. The rings are actually made of a number of ringlets

influenced by Saturns moons. At last count, Saturn has 62 moons, many of which aresmall and only discovered within the last decade.

Titan - The largest moon by far is Titan. Its larger than both Mercury and our Moon, andthe only largest planetary satellite in our solar system is Jupiters Ganymede. Titan was

discovered by Christian Huygens. The Huygens probe which descended into Titans

atmosphere is named after him. Observations show it has an atmosphere mostly made up

of nitrogen, but it also has a decent amount of hydrocarbons such as methane. Thehydrocarbons rain down to form lakes of methane and ethane. Evidence suggests Titan has

hundreds of times more liquid hydrocarbons than the known oil and natural gas reserves on

Earth.

Moon - The Moon is our only satellite. It was most likely formed when a large, Mars-sized

plenetesimal struck the Earth and threw debris into orbit around the Earth. The Moonformed from that debris. When its out, it is the brightest object in the night sky. The light

colored parts of the Moon are the lunar highlands; theyre generally covered with craters.

The darker maria formed from later lava flows and have fewer craters than the lunarhighlands because of it.

Mercury - This is an image of Mercury captured by the MESSENGER orbiter. Mercury

will be visible for some time over the summer. It will be trailing behind the setting Sun.

The Summer Triangle - Vega in Lyra (the brightest), Altair in Aquila, Deneb in Cygnus

Lyra - Originally shown as a vulture carrying a lyre, it is now usually just illustrated as a

lyre.

M57 - The diameter is estimated to be ~0.5 ly. It is overwhelmingly hydrogen and helium.

The visual blue-green color comes from doubly ionized oxygen, and we see it over the

other colors because our eyes are more sensitive to it. In the center, there is the remains of

the core of the star cooling to become a white dwarf.

Planetary Nebula - When relatively low-mass (~ 4 solar masses) stars near the end of their

evolution, they run out of hydrogen in the core to use for fusion. The core at this point isalmost entirely helium. At this point, the only hydrogen fusion going on is in the shell just

outside the core where hydrogen remains. With the end of hydrogen fusion in the core, it

compresses and heats up. The heat flows to the shell of hydrogen rich material outside thecore. This increases the rate of shell hydrogen fusion, and the outer layers expand due to

the heat of the core. The star becomes a red giant. The hydrogen fusing shell adds mass to

helium core. As the core heats and shrinks from the added mass, helium fusion begins in

the core. As it starts to use helium in the core as fuel, the core expands and cools, and the

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hydrogen-fusing shell around the core also cools. The rate of energy release is slowed, and

the outer layers are able to contract. Helium fusion in the core ultimately produces carbon

and oxygen. The helium in the core is used up, and the core then cools and shrinks. Thecore heats up due to compression, and as the heat flows from the core to the shell, shell

helium fusion begins. Again, increased energy output causes the outer layers to expand,

and the star starts a second red giant phase. As helium is used up in the shell, contractionoccurs. A second shell of material still containing hydrogen heats up until hydrogen fusion

occurs in this second shell. The second shell with hydrogen fusion rains helium upon what

is now a dormant helium shell, and once a critical value is reached, a helium shell flashoccurs which reignites the shell helium fusion. When the helium shell flash occurs, the

luminosity of the star briefly increases in a thermal pulse. During a thermal pulse, outer

layers of material can be stripped from the star. This occurs multiple times, and a planetary

nebula forms from the resulting material. Stars between 4 and 8 solar masses also produceplanetary nebula, and their evolution is similar with a few differences.

RR Lyrae - It is the typical example of the RR Lyrae variables and is the brightest of them.

RR Lyrae are standard candles; they are objects whose intrinsic brightness astronomers candetermine, and after measuring how bright they appear to us, their distance can be

calculated. RR Lyrae stars pulse and change in brightness. When gravitationalcompression occurs, some of the work done on the gas produces further ionization in

partial ionization zones. This increases the opacity, which causes a buildup of energy, and

this will result in expansion. During expansion, ions recombine with electrons, and theopacity decreases. This allows more energy to be released, and the star can compress.

Their pulsation periods are related to their intrinsic brightness. Theyre often found in

globular clusters and are occasionally called cluster variables.

Distance Ladder - RR Lyrae variables are part of a toolbox for astronomers known as the

distance ladder. The first step is parallax; as the Earth moves around the Sun, nearby stars

will appear to move in relation to further background stars. Using geometry, their distancecan be calculated. Spectroscopic parallax uses a star's spectral class to determine it's

luminosity. This can be used to find its distance. RR Lyrae and Delta Cephei stars both

pulsate with periods related to their absolute magnitude. The Tully-Fisher relationship isused to find the distance to spiral galaxies. The approaching side of the galaxy is blue-

shifted and the receding side is red-shifted. This makes the hydrogen 21-cm line broader

the faster it rotates. Rotation speed is related to the galaxy's mass. The more massive it is,

the more luminous it is. Once the luminosity is found, the distance can be determined.There is a relationship between an elliptical galaxy's size, motion, and the distribution of

brightness over the galaxy's surface. By measuring the brightness and motion, the size can

be determined. Comparing the apparent size and the actual size allows the distance to becalculated. There is a relationship between the peak magnitude of a type IA supernova and

how fast its brightness falls off. Also, red-shift and Hubble constant.

Aquila - Altair in Aquila helps form the Summer Triangle. In classical mythology, Aquila

was an eagle that served Zeus.

Cygnus -

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Albireo - A great double star to view with very vivid colors. It appears to be a single star

to the naked eye. The brighter star, Albireo A, is in fact a binary star. It is not known ifAlbireo A and Albireo B are a gravitationally bound to each other in a binary system.

Cygnus X-1 - One of the strongest X-ray sources in the sky. It has not been directlyobserved. It has a visible companion of 9th magnitude. It has been determined that the star

is feeding the unseen object. Its mass is much higher than what is known for a white

dwarf and what is thought to be the maximum mass for a neutron star.

North America Nebula -

Hercules -

M13 and M92 - Globular clusters are comparatively densely packed star clusters containing

~1 million stars and are a few hundred light-years across. They orbit the galactic center,

but they don't lie in the plane of the galaxy. M13 is one of the best globular clusters in thenorthern hemisphere. Fitting observations of the M13 to a theoretical H-R diagram, we can

calculate an age of 10 billion years for the cluster. M92 is another nice globular cluster inHercules.

Libra - Libra was to the Greeks the claws of the Scorpion. Many other civilizations,though, have identified it as scales.

Gliese 581 - Recently, there was an interesting announcement of a rocky planet in the

habitable zone of the star Gliese 581. This planet is designated Gliese 581 g. It's notshown on this graph because it is unconfirmed. There have been arguments over its

existence, and nothing conclusive seems to have popped up. Gliese 581 d, on the other

hand, is a confirmed exoplanet, and depending on its atmosphere, might lie in the habitablezone.

Scorpius - It is classically the scorpion that killed Orion the hunter.

Antares - Its name means the Rival of Mars, and it is named for its red color. It is a red

supergiant.

Ophiuchus and Serpens - Ophiuchus is the serpent holder. Serpens is unique among

constellations in that it is split into two parts: Serpens Caput and Serpens Cauda.

Globular Clusters - Because of its proximity to the galactic center, Ophiuchus has a number

of globular clusters in it.

M16 - The Eagle Nebula is probably one of the first things people think of when a nebula is

mentioned largely due to the HST picture the Pillars of Creation. Oddly enough, the

Pillars of Creation were most likely destroyed due to a supernova ~6000 years ago. The

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shockwave of the supernova has been observed. Since the nebula is ~7000 ly away, we

will be able to observe the pillars for another millennia.

Sagittarius -

Omega, Trifid, and Lagoon Nebula -

The Galactic Center -

Barred Spiral - Spiral arms originate from the bar-shaped region running through the center

Our Location - Orion Arm

Supermassive Black Hole - Feeding a normal black hole possibly formed in the big bang,

dust and gas collapsing to form a large neutron star to black hole, not well understood.