Gathering Light

How much you can see with any telescope is governed by its aperture. Larger apertures collect more light, thereby showing fainter objects and finer detail. however, large lenses are expensive to make, are heavy, and require longer tubes. As a result, for telescopes with apertures greater than about 4 inches (100 mm), amateur astronomers usually turn to reflectors, which use mirrors, and catadioptrics, a hybrid design. All large professional telescopes are reflectors. Computer-controlled...

Monoceros

The charts show the major stars and deep-sky objects in each constellation. Individual stars are represented by dots that indicate their apparent magnitude (see scale at bottom of page). Distant, nebulous objects, such as clusters of stars, nebulae, and galaxies, are known as deep-sky objects. These are indicated on the constellation maps by the icons shown on the right. All are labeled with a catalog number, which may be a Messier number or an NGC or IC number (see p.147). Planetary nebula or...

Info

Main-sequence stars generate energy by nuclear fusion of hydrogen in their cores. When supplies are exhausted, they find a new source of power burning the helium they have spent their lives generating, and perhaps other, heavier elements. These changes in the star's energy supply make it unstable, causing it to swell to giant size. The star's ultimate demise is determined, like most aspects of its evolution, by its mass. The most massive stars may eventually detonate in supernovae, leaving...

The Scale Of The Universe

The universe is so vast that it is almost impossible to grasp. One way to get a feel for its size is to use a series of astronomical stepping stones from a planet, to a solar system, to a galaxy, and beyond. The planets are lost in the space of the solar system orbiting the Sun at distances ranging from tens of millions to billions of miles. The Sun itself is a typical middle-aged star, with a diameter of 865,000 miles (1.4 million km). The planets are lost in the space of the solar system...

Lacerta

In this CCD Image, the Garnet Star, Mu (m) Cephei, appears above the nebula IC1396, which Is centered on Struve 2816, a 6th-magnitude multiple star. To gauge the magnitude of the variable stars Delta (5) and Mu (m) Cephei at any given time, their brightness can be compared to that of nonvariable stars nearby. Useful yardsticks are Zeta (Z) Cephei (magnitude 3.4), Epsilon (e) Cephei (magnitude 4.2), and Lambda (l) Cephei (magnitude 5.1). width ll depth ll size RANKING 25111 fuLLY vislBLE 90 n-12...

Mars

Rust-red Mars is the fourth planet from the sun. This dry, cold world is about half the size of Earth. Giant volcanoes, deep faults, rock-strewn plains, and dried-up riverbeds mark its surface. Like earth, it has polar ice caps and seasons. this ball of rock and metal is the outermost rocky planet. When it was young and molten, its material differentiated to form a core and layers. the heavy iron sank to the center, and the lighter silicate rocks formed a mantle around the metallic core. the...

Musca

This nebula appears as a dark patch In the bright Milky Way next to the stars of the Southern Cross, here at center left. Alpha and Beta Centauri are at far left, while the Eta Carinae Nebula is the pink patch just right of center. ngc 4755 (the jewel box cluster) 2 1 5 An open cluster that is one of the gems of the southern sky, visible to the naked eye as a brighter patch in the Milky Way. Binoculars and small telescopes show its individual stars covering about one-third the apparent width of...

Saturn

Saturn is the sixth planet from the Sun and is twice as far from Earth as Jupiter. Its most distinctive feature is the complex system of rings that surrounds it. The planet, which has a muted, banded surface, has a large family of moons. Saturn is the second-largest and least dense of all the planets. It is made of 95 times the amount of material in Earth, but it occupies a much greater volume. About 764 planets the size of Earth could fit inside Saturn. The planet is composed of hydrogen and...

The Andromeda Galaxy

The most distant object normally visible to the naked eye, this galaxy appears as a faint misty patch, elongated because it is tilted at an angle to us. Binoculars reveal more of its extent, and through telescopes signs of its spiral arms can be traced. GAMMA (y) andromedae 5 A showpiece double star consisting of an orange giant star of magnitude 2.3 with a contrasting blue companion of magnitude 4.8, easily divided with small telescopes. M31 (THE ANDROMEDA GALAxy) 2 1 5 A huge spiral galaxy...

Eftune

The Great Dark Spot Is in the center of the disk in this 1989 Voyager 2 image. The short-lived storm was gone when the Hubble Space Telescope looked for it in the mid-1990s. Thirteen moons are known to orbit Neptune, and more small ones probably exist. Just one of the moons, Triton, is large and round. The innermost four lie within the ring system. This consists of five complete rings, the outer of which contains three dense regions of material, as well as a sixth partial ring. The rings are...

The Invisible Universe

Until the middle of the 20th century, astronomers could only study celestial objects through the radiation they emitted at visible wavelengths. But visible light is only a tiny portion of the spectrum of electromagnetic waves, ranging from extremely long-wavelength radio waves to short-wavelength gamma rays. Short wavelengths in particular are very damaging to living tissue, but fortunately Earth's atmosphere blocks out nearly all wavelengths except for visible light and some radio waves....

Finding The South Pole

In the southern sky, the southern Cross acts as a pointer to the celestial pole. Extend the long axis of the Cross fivefold to reach the southern pole, an area bereft of any stars of note. As a further rough guide, the south celestial pole forms a triangle with the bright stars Canopus and Achernar. 1 First, locate the familiar shape of Crux, the Southern Cross (highest on April and May evenings). It is one of the smallest constellations but also one of the most distinctive. Then locate the two...

Medieval Astrolabe

Widely used in medieval times, an astrolabe is a disc-shaped device used for finding latitude and measuring time by sighting on stars, like a sextant. The stars and nebulae visible to our unaided eyes all lie within our own galaxy, the Milky way. Binoculars and small telescopes expand our horizons to other galaxies millions of light-years beyond, while modern instruments have stretched our visual limits to a few hundred thousand years from the Big Bang, the cosmic eruption that marked the birth...

Reflecting Telescopes

Reflecting telescopes employ mirrors to collect light and focus it into the eyepiece. A concave main mirror serves the same purpose as the objective lens in a refractor. the main mirror lies at the bottom end of the tube. Light falling on it is reflected back up the tube to a smaller mirror, known as the secondary, which diverts the beam into an eyepiece at the side of the tube. the design is termed a Newtonian, after Isaac newton, who first devised it, and is the type most commonly used.

Cassiopeia

Width ll depth ll size RANKING 18th fuLLY vislBLE 90 n-3 s Camelopardalis is a large but dim constellation of the far northern sky, representing a giraffe. Its long neck stretches around the north celestial pole between Ursa Minor and the tail of Draco. Not one of northern the original Greek constellations, HEMispHERE it was introduced in the early 17 th century by the Dutch astronomer Petrus Plancius. Like drops of water squirted from a toy pistol, the stars of Kemble's Cascade extend for five...

M81 And M82

These two contrasting spiral galaxies are found in northern Ursa Major. The larger of them, M81, is visible on clear, dark nights as a slightly elongated patch of light. One full-moon diameter to the north of it is the smaller, fainter M82, which will require a telescope to be spotted. The familiar saucepan shape of the Big Dipper is one of the most easily recognized patterns in the sky, but makes up only part of Ursa Major. The second star in the handle can be seen to be double with the...

Neptune

Faraway Neptune was only discovered in 1846 and remained poorly known until Voyager 2 flew by in 1989. The probe revealed a cold, blue world encircled by rings and moons, with a surprisingly dynamic atmosphere. layer of water, methane, and ammonia ices atmosphere of hydrogen, helium, and methane gases layer of water, methane, and ammonia ices atmosphere of hydrogen, helium, and methane gases Neptune has no solid surface its visible surface is the top of its atmosphere. Inside, the planet is...

Binoculars

Binoculars are the ideal instrument for beginners. They are cheap, portable, easy to use, and will help you learn your way around the night sky before you move on to a telescope. Binoculars can be thought of as two small telescopes fixed together. Inside the binocular, two prisms fold up the light path, making them more compact than a normal telescope. Every binocular is marked with two numbers, such as 7 x 40 or 10 x 50. The first figure is the magnification, which is the enlargement relative...

Cosmic Distances

The vastness of the universe can only be represented with a logarithmic scale. On the chart below, the first division represents 6,200 miles (10,000 km). Each further division marks a 10X increase in scale on the previous one (not all divisions are labeled). is nothing beyond the universe for it to border but because space and time can be warped by gravity, the universe might curve in strange ways, perhaps even folding back on itself in places.

During

Supernova Glowing Ghost

Once a Sun-like star has shed its outer layers as a planetary nebula, only the core region remains. Typically this is a ball of dense, hot matter, about the size of Earth and glowing intensely White dwarfs are so faint that very few are within reach of amateur astronomers. In addition, two of the brightest (Sirius B and Procyon B) are companions of extremely bright stars. The easiest example to spot is Omicron2 Eridani. procyon b 10.7 Canis Minor omicron2 Eridani 9.5 Eridanus van Maanen's Star...

Astrophotography

Photography has two main advantages over visual observing it keeps a permanent record of what is seen, and long exposures can build up images of objects far fainter than those visible to the naked eye. Astrophotography is a popular occupation for many amateurs. Digital imaging has almost completely supplanted film for astrophotography, as it has with normal photography. Digital cameras contain light-sensitive silicon chips known as charge-coupled devices (CCDs). CCDs have many advantages over...

Southern Hemisphere

Epsilon (e) lupi 5 A 3rd-magnitude star with a companion of 9th magnitude that becomes visible with small telescopes. Kappa (k) lupi 5 A double star with components of 4th and 6th magnitudes that are easily divided with small telescopes. MU (m) lupi 5 An interesting multiple star. Small telescopes show a 4th-magnitude star with a wide 7th-magnitude companion. The primary star is itself a close double, requiring apertures of at least 4 in (100 mm) to separate. XI lupi 5 A double of 5th and 6th...

The Constellations

Astronomers divide the celestial sphere into sections called constellations. These originated with the star patterns imagined by ancient people to represent their mythical heroes, gods, and exotic beasts. Now, constellations are simply areas of sky with boundaries laid down by international agreement, although the ancient names such as Perseus, Andromeda, and Orion have been retained. A catalog of stars divided into 48 constellations was produced around ad 150 by a Greek astronomer and...

Space Shuttle

Despite its problems, the Space Shuttle has been a major step forward in spaceflight, carrying out more than 100 successful missions and pointing the way for future reusable spacecraft. The breakup of Columbia following damage to its insulating tiles led to a decision to retire all the shuttles once the ISS is completed, by 2010. There was also the question of the Shuttle's purpose the satellite launch market was becoming increasingly competitive as other countries developed their own launch...

Comet Borrelly

The comet's 5-mile-(8-km-) long nucleus is shaped like a bowling pin. Gas and dust jets are emitted from its surface. Borrelly is a short-period comet it returns every 6.86 years. tails are longest dust tail gas tail is straight close to the Sun, is curved, ,and narrow tails are longest dust tail gas tail is straight close to the Sun, is curved, ,and narrow a comet's tail always points away from the Sun tail grows as the comet travels toward the Sun tail shrinks as the comet moves away

Mercury

Mercury is the closest planet to the sun. A dry, rocky, cratered world, it feels the full force of the sun's heat during the day, but, with only the barest of atmospheres, experiences freezing cold nights. It is difficult to study from Earth and largely unexplored. Below mercury's silicate rock surface is a solid rocky mantle about 340 miles (550 km) thick. This layer would have been liquid when mercury was young, and the source of volcanic eruptions. Mercury is extremely dense compared with...

Fine Dust

The lunar soil, termed regolith, is fine-grained, fragmented bedrock. It is dustlike on the surface, but the grains get larger with depth. Astronauts' boots left crisp footprints. The Moon takes 27.3 days to complete one elliptical orbit around Earth. As it moves, Earth orbits around the Sun. It takes 29.5 days for the Moon to return to the same position relative to the Sun in Earth's sky, and complete its cycle of phases. The Moon's gravity pulls on Earth, making the oceans on either side of...

Z Hydrae Magnitude

BETA (P) monocerotis 5 One of the finest triple stars in the sky for small telescopes, consisting of an arc of three 5th-magnitude stars. EpsiLON (e) monocerotis 5 A double star-on some charts labeled 8 Monocerotis with components of 4th and 7th magnitudes. M50 K 5 An open cluster about half the apparent size of a full moon, visible in binoculars but requiring telescopes to resolve individual stars. NGC 2244 K 5 S A group of stars of 6th magnitude and fainter, visible through binoculars. The...

Landscape About Maat Mons Venus Planet

Venus is similar to Earth in size and structure, and is our inner neighbor, the planet that gets closest to us and appears larger than any other in our sky. Yet it reveals little of itself only a top layer of thick, unbroken blanket of cloud is visible. In diameter, Venus is only about 400 miles (650 km) smaller than Earth, and its internal layers are of similar size and composition. Below its silicate crust is a rocky mantle, and below this a core, which is solid in the center. It spins on its...

Ngc 2017

This chance grouping of stars resembles a small cluster. The disks and spikes are effects of the large professional telescope through which the picture was taken. GAMMA (g) LEPORiS 5 A 4th-magnitude yellow star with a 6th-magnitude orange companion visible through binoculars. KAPPA (k) LEPORiS 5 A 4th-magnitude star with a close 7th-magnitude companion, difficult to separate with the smallest apertures. R LEPORiS 15 A variable star of the same type as Mira, noted for its intensely red color....

Features Of Interest

ALPHA (a) CYGNI (DENEB) 2 An immensely luminous supergiant. At magnitude 1.3 and over 3,000 light-years away, it is the most distant first-magnitude star. BETA (P) CYGNI (ALBIREO) 5 A beautiful colored double star in the beak of the swan. The two stars can just be seen separately through binoculars, if steadily mounted, and are an easy target for a small telescope. The brighter star, magnitude 3.1, is orange and contrasts strikingly with the fainter one, magnitude 5.1, which is blue-green....