The purpose of this book is to serve as a reference and, hopefully, inspiration for when you are thinking about "what should I image tonight?" My goal is to provide you with examples of the beautiful objects in the deep-sky that you can shoot with your own equipment.
500 potential photographic targets are listed in a Master List of Objects including:
- Bright stars
- Double stars
- Multiple stars
- Variable stars
- Carbon stars
- Open star clusters
- Globular star clusters
- Stellar associations
- Wide-Field selected areas
- Emission nebulae
- Planetary nebulae
- Reflection nebulae
- Dark nebulae
- Supernova remnants
- Molecular clouds
- Galaxy groups
- Galaxy clusters
Images of more than 275 of these objects are included in the book and each is described in detail on individual pages.
I've also included lots of objects in the master list that I haven't had a chance to shoot yet, but that are still interesting targets.
The book is aimed primarily at astrophotographers, but should be of interest to visual observers also.
In general, I have included photographs of most of the largest and brightest objects and a few really faint and challenging objects that nevertheless make wonderful images.
Constellations are placed into seasonal groupings more or less based on when the center of the constellation is transiting the meridian at midnight local time (or 1 a.m. daylight savings time). This gives us the longest amount of time to observe or photograph the constellation or objects in it when it is highest in the sky. This way we can start shooting before it transits and continue shooting after it transits and it will still be relatively high in the sky.
Almost all of the images in this book were shot with DSLR cameras with exposures that range from a few minutes to several hours. Fainter objects require longer exposures. Refer to the Photography Notes section for more information.
How To Use This Book
If you are planning an observing session, use the Local Sidereal Time Calculator to determine the hour of right ascension that will be on the meridian when you plan to image. Then go to the Master List of Objects and scroll down to that right ascension to see which objects will be best placed for shooting.
To read the book I suggest trying the full-screen mode of your web browser. Most browsers use the F11 key on the keyboard to enter full-screen mode. Hit the F11 key again to exit full-screen mode.
I would also suggest copying the entire book (about 100mb) to your hard drive where it will work much faster. But please don't copy it to a server on the internet where it can be found by search engines even if you think it is private. Because I make my living and support my family by selling my books, if people can find a free copy on the internet, they are not going to buy it. For the same reasons, please don't make copies and give them to your friends. Thank you for your understanding.
This book is organized so that you can find an object by the various methods listed below.
Individual Image Pages
Each image page in the book has information about the objects in the individual images as well as a data box labeled "Exposure Data" describing how the image was shot. A general finder chart and a data list with the main object's primary information such as size, brightness and location are also included.
Field of View - Two sets of numbers are included for each image.
Image Field of View gives the size of the image after cropping as it is displayed on the page in this book. Cropping means to cut off the sides of an image for aesthetic purposes to make the main subject appear larger in the final image. Don't be afraid to crop your images. If it's well exposed and focused and only for web presentation, you will be surprised at how much you can crop an image. On the other hand, there is a limit to how much you can crop if you want to make big prints that require high-resolution in a large image file.
Camera Field of View gives the size of the field of view of the telescope or camera lens uncropped when shot with an APS-C sized camera sensor (These are about 22.3 mm x 14.9 mm in size, such as in the Canon T2i (550D), T3i (600D), T4i (650D), T5i (700D), 20Da, 30D, 40D, 50D, 60D, 60Da, 70D, and others).
Note that the fields-of-view listed are sometimes slightly different than what is calculated with the field-of-view calculator on the Photography Notes appendix page, or from the focal length marked on the scope or lens. This can be caused by a variety of factors, such as manufacturer variations, focal length change due to temperature fluctuations, or spacing changes between a focal reducer or field flattener and the sensor causing a change in focal length.
Sizes for objects and constellations are given in both arcminutes and degrees in the Master Objects List. These are usually approximations as most constellations are not perfectly square or rectangular.
Object sizes are sometimes approximations also as many objects seem to grow in size as faint parts become visible in longer exposures.
To give a sense of scale, the Moon is one-half of a degree in diameter. The Orion Nebula is about 1.5 x 1 degrees in size. The entire sphere of the sky is more than 40,000 square degrees in size. The one hemisphere that is visible at any given time is more than 20,000 square degrees.
The focal length of your lens or telescope and size of your image sensor determine the field of view of your setup.
Object Magnitudes - Stars are so far away in the night sky that they essentially are point sources from our viewpoint. The magnitude of a star tells how bright it appears to us. Comparisons of the apparent brightness of different stars are straightforward because they can be directly compared.
Deep-sky objects, on the other hand, are extended objects. This means that they are larger than a point and cover a measurable area of sky. Some are small and some are very large.
When a magnitude is given for an extended object, it is usually an integrated magnitude. This means all of the light from the object is considered essentially as a point source. Unfortunately, this can be confusing and misleading to beginners in astronomy and astrophotography.
For example, two objects may have exactly the same integrated magnitude, but the object that is larger in apparent size will appear dimmer, both visually and in an image. This is because the same amount of light is spread out over a larger area.
Deep-sky object magnitudes and sizes can also be misleading because many objects like galaxies and globular clusters have a bright core and fainter outer portions that eventually fade to blend in with the brightness of the sky background. We might only record the brightest portion of an object is our exposure is short, or if the brightness of the sky background washes out the fainter parts.
Object Location is given in right ascension (R.A.) and declination (Dec), one of the standard coordinate systems for astronomical objects. These correspond to longitude and latitude on the earth, but projected onto the celestial sphere. A circle around the celestial sphere contains 360 degrees. Each degree is divided into 60 arcminutes, and each arcminute into 60 arcseconds. These are not measurements of time, but of angle.
Exact coordinates are give for the center of the field of each image as determined by the plate-solving software AstroTortilla, which incorporates the Astrometry.net plate-solving engine.
Finder Charts - Each image page includes a wide-field finder chart to give you a general idea of where an object is located in the sky. These charts are from Cartes du Ciel, a great freeware planetarium program by Patrick Chevalley, who has kindly given his permission for them to be used in this book.
Any text in the book that is underlined is a link. Some links, such as the navigation links at the top and bottom of every page are not underlined for design and organizational purposes, but if you hold your mouse cursor over this text, an underline will appear, indicating that it is a link.
There is a convention in astronomy of presenting images of objects with north to the top of the frame. But I do not strictly follow this tradition for practical and aesthetic reasons. For example, for northern circumpolar constellations, such as Cassiopeia and Ursa Major, presenting them with north up is not when they are best viewed in the sky. With north up they would be below Polaris and lowest in the sky. Therefore I present some objects with south up, and some rotated 90 degrees for reasons of composition. The orientation of an object can also change as it rises in the east, moves across the sky, and sets in the west. Object pages note the orientation of the image in the text. Constellation image maps show the direction of north in the image.
The size of the text in the book can be adjusted to make it more readable. Most web browsers will magnify the page by using the control and + keys on your keyboard to increase the page size, or the control and - keys to decrease the page size.
In the first draft of this book, I qualified most deep-sky object distances and sizes by saying "about". For example, I said that M31, the Andromeda Galaxy, is located "about" 2.5 million light-years from Earth. This is the current best figure, but it is the fundamental nature of science that these types of numbers change as better data comes in. Some distances are not well know - in those cases I gave a range, again qualified by using the word "about." But this became boringly repetitive, so I removed all of the "abouts" in the text of the book.
You should note that whenever a figure is given for a distance or size, it is the current commonly accepted quantity, but that most of these figures are not exact and that they can change in the future.