天文摄影的100个最佳目标

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"The 100 Best Targets for Astrophotography" 是一本电子书，由 Ruben Kier 编写，适合使用业余天文望远镜进行CCD成像的天文爱好者。书中提供了每个月最佳的天文摄影目标，涵盖各种天体类型，如星云、星团、星系等。一：书中详细列出了12个月份的不同天文摄影目标。1月主要是星云，2月是星团和星云的组合，3月是星团和星系，4月关注星系群，5月探讨了多样化的星系形状，6月是球状星团和更多星系，7月专门聚焦球状星团，8月转为行星状和发射星云，9月是秋季的混合选择，10月的主题是“万圣节礼物”，11月重点在伟大的星系，12月则是天文物体的大杂烩。这些目标的选择旨在为天文摄影提供多样性和挑战性。二：除了列出摄影目标，书中还涉及了"Getting Started in CCD Imaging"，即如何开始CCD成像。这部分内容涵盖了天文摄影所需设备，如CCD相机、望远镜等，并讲解了如何获取图像以及图像处理的顺序，这对于初学者来说是非常宝贵的指导。作者可能详细讨论了如何正确设置和操作设备，如何对焦，以及如何进行黑暗帧、偏置帧和平坦帧的拍摄以消除噪声和畸变。此外，还可能涉及图像的叠加、减影、色彩恢复和最终图像的优化技巧。这本书属于Patrick Moore's Practical Astronomy Series，是一套专门针对实际天文观测和摄影的丛书。Springer Science+Business Media出版，具有国际标准书号（ISBN）和数字对象标识符（DOI），并强调未经许可不得非法复制或翻译，尊重版权。书中可能还会包含对各种商业品牌、商标和服务标记的提及，但这并不表示作者对其是否受知识产权保护的意见。通过阅读这本书，读者不仅可以了解到一年四季中每个月最适合拍摄的天文目标，还能掌握CCD成像的基础知识和实践技巧，从而提升天文摄影水平。对于爱好天文摄影的业余天文学家而言，这是一本极具价值的参考资料。

Introduction

Caldwell-Moore) of 109 objects, which includes both bright and dim

objects excluded by Messier. His selection includes some small and

challenging targets, not just the crowd pleasers. Most recently, in 2007,

Stephen O’Meara published a list of 109 “hidden treasures” that seeks to

fill in the gap left by the Messier and Caldwell lists. Like the Caldwell list,

O’Meara’s list dips deep into the southern hemisphere.

These famous lists are excellent for visual astronomy but can be dis-

appointing for the astrophotographer. For example, a sparse open

star cluster sparkles at the eyepiece but can be uninspiring as an

image. A small planetary nebula may be striking visually but may be

too small to show interesting detail in a photograph. On the other hand,

many nebulae that are faint to the eye can have striking texture and

hue on long exposures. Spiral galaxies blossom into a rich diversity of

shapes and colors.

How the Targets Were Chosen

This book showcases the 100 best targets available to backyard astro-

photographers in the Northern Hemisphere. These selections include 48

Messier, 28 Caldwell, and 13 O’Meara objects, plus several others cited in

catalogs by Arp, Hickson, Sharpless, and Barnard. Almost a third of the

targets can be framed to include multiple objects. The criteria for inclu-

sion were simple:

• Doestheimageinspiretheviewer?

• Isthe objectbright enoughto image witha backyardamateurtele-

scope,anaverageCCDcamera,and2–3hofexposure?

• Isitlargeenoughtoshowdetail,usually5arcminormore?

• Can it be photographed successfully from northern latitudes? (This

usually requires a declination above –25°.)

Other features favoring inclusion are:

• Amongsimilarobjects,isittheeasiesttoimagebecauseofdeclination,

size,color,orbrightness?

• Cantheobjectbeframedwithasecondobjecttocreateamoredynamic

image?

The images on the following pages represent what an average amateur can

expect to accomplish with some practice and effort. In some cases, with

xviii

Introduction

modest equipment, you can expect to approach the efforts of the best

imagers who use large format cameras through sophisticated astrographs

on monolithic mounts. In other cases, a more humble image can be quite

satisfying. In every case, you will be capturing views of celestial objects

matching or surpassing the photographs taken only decades ago from the

finest observatories such as Palomar, Lick, Mt. Wilson, and Lowell.

Our goal is to walk you through the steps of choosing an object,

acquiring the image, and then processing the data until you say, “Wow!”

The date at the top of each entry indicates the day when the target is on

the meridian at 9 p.m. standard time (10 p.m. daylight savings time)

for observers in the center of their time zone. Accompanying each illus-

tration, the first paragraph gives a brief background about the object

and its significance. A second paragraph advises on how to acquire the

image, including suggestions on framing, exposures, binning, guiding,

and filters. A third paragraph provides specific suggestions for process-

ing the object.

The second section of this book is a brief introduction to digital astro-

photography, with an emphasis on CCD imaging with moderately priced

equipment. For beginners, we have tried to keep explanations straight-

forward. For more advanced imagers, we have included some pointers

gained from experience (i.e., mistakes!).

What Are We Looking at?

At the beginning of time, the Big Bang spread mostly hydrogen and some

helium into the early inflating universe. These gases condensed into the

giant luminous stars that populated young, unstructured galaxies,

barren of planets, burning brightly yet briefly, and then dying violently in

the cataclysm of supernova explosions. These blasts created the heavy

elements, which produced the wide expanses of interstellar dust that drift

among the Milky Way’s spiral arms. Other gravitational interactions

collapsed this dust and gas into new generations of stars. These descend-

ants have evolved into the spectacular diversity of clusters, nebulae, and

galaxies that entice the astronomer in all of us.

The following 100 targets include 21 images dominated by emission

nebulae, often in combination with an open cluster. Clouds of gas and

dust abound in our galaxy. In interstellar space, far from any star, the

gas is cold and dark. In some cases, a portion of the gas cloud collapses

under its own gravity to generate young bright O and B type stars, which

form an associated open star cluster. The ultraviolet light from these new

stars ionizes the surrounding gas, stripping off electrons. When the

xix

Introduction

electrons recombine with ions, they release photons of discrete energy

(and thus discrete wavelengths) as the electrons cascade back down to

a lower energy level. One of these wavelengths is termed the hydrogen

alpha band, which contributes to the red glow of emission nebula and

allows us to image these nebulae with H-alpha filters.

These pages also include six images dominated by reflection nebulae.

In these cases, interstellar dust contributes up to 2% of the mass in a gas

cloud. These microscopic particles of dust collectively reflect the blue light

of nearby stars, both because they are usually associated with young hot

stars that shine blue-white, and because dust is more effective in reflecting

blue light than red light. For much the same reason, the dust in Earth’s

atmosphere reflects sunlight to make our sky blue. However, as the dust

becomes denser, or collects farther from any stars, it may actually block

the light of stars or the glow of hydrogen emission, giving rise to a dark

nebula. Depending on the distribution of gas and dust, many of these

images contain mixtures of emission, reflection, and dark nebulosity.

With time, the solar winds of these young stars disperse surrounding

clouds of dust and gas. They leave the open star clusters shining alone,

as illustrated in nine images. The younger clusters will appear to shine

blue-white in our images, not because their stars are all the same color

but because the red and yellow stars are much dimmer than the blue and

white stars. As star clusters age, the short-lived blue stars expire, and the

remaining white and yellow stars begin to dominate our images.

An extreme example of stellar evolution is seen in the seven images of

globular clusters. These ancient dense clusters of hundreds of thousands of

stars are at least 12 billion years old. White and yellow stars comprise most

of the stars in the cluster, appearing as countless tiny points of light that

appear to merge in the core of the globular cluster. Scattered red giants,

swollen to luminosity a hundred times greater at the end of their lifespan,

become the largest and brightest individual stars within the image.

Eighteen images show stars at the end of their stellar evolution, either

as planetary nebulae (11 images), Wolf–Rayet stars (3 images), and

supernova remnants (4 images). Planetary nebulae are created by dying

stars that blow off their outer layers once their central supply of fuel is

exhausted. The remnant central star is a dense “white dwarf” that can

no longer support nuclear reactions, yet provides the ultraviolet torch

that illuminates the outer shells of gas. Whereas the lifespan of the star is

measured in billions of years, the stunning colors of the planetary nebula

last a mere thousand years. Thus, upon their deaths, these stars impart to

the universe a brief but memorable gift of beauty.

Thirty-nine images emphasize galaxies. Most are variations of spiral

galaxies, including face-on pinwheels, edge-on cylinders, and several

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天文摄影的100个最佳目标

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