By DK Publishing
For someone who's ever checked out the evening sky and desired to be aware of extra in regards to the galaxy round them, The useful Astronomer indicates readers the best way to become aware of and comprehend the mysteries of the sun approach and past.
Illustrated all through with unique pictures and illustrations, and utilizing transparent, easy-to-follow textual content, The useful Astronomer takes you on a step by step trip from the fundamentals of what may be visible with the bare eye, to how one can view extra far away items corresponding to the planets of the sun process, or even galaxies a ways, a long way away-all on your personal yard.
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Extra resources for The Practical Astronomer
Declinations between the equator and the north celestial pole have positive values; those between the equator and the south celestial pole, negative. Right ascension (RA) seems more complex because it uses hours and minutes rather than degrees for its measurement scale. One hour of RA across the celestial sphere is equivalent to 15° of longitude here on the Earth. The reason time is used instead of an angle is because in one hour the sky appears to turn through 15°. The line of zero RA, or the celestial meridian, is marked at the moment when the Sun, moving northward along the ecliptic, crosses the celestial equator.
Earth’s orbit Sun Noon on ﬁrst day Earth’s rotation Second noon in solar time Second noon in sidereal time (4 minutes earlier than solar time) 34 LOOKING UP The Earth’s orbit and the ecliptic The deﬁnition of one year is the time it takes the Earth to orbit the Sun once. Of course, from our ﬁxed Earth-centered perspective, the roles seem to be reversed and it appears as though the Sun travels around us. If you imagine that the Sun could leave an imprint in the sky at the same time of day, every day for a year, then after one year, we would see a complete circle around us.
So a telescope with a focal length of 2,500mm used with an eyepiece with a focal length of 25mm gives a magniﬁcation of 100 times. Changing the eyepiece changes magniﬁcation, but only within practical limits set by the aperture of the telescope (see table, right). As a Objective general rule, it is wise not to use an lens eyepiece that gives a magniﬁcation greater than twice the size of the telescope’s objective (in mm). 9mm EYEPIECE Tube BASIC OPTICS This telescope is a refractor, using lenses (not mirrors) to form an image.
The Practical Astronomer by DK Publishing