The moon's orbit is tilted 5 degrees from the Earth's and rises and falls as it orbits, like the horses on a carousel. Around that time of the month, the moon is invisible in the sky next to the sun's glare, and the hemisphere of the moon that is illuminated points away from Earth. New moons occur when the moon crosses the imaginary line connecting the sun and the Earth, coming between the two.
The sunlight falls across features at a steep angle and casts inky black shadows, especially along the pole-to-pole boundary line separating the lit and dark portions, which is called the terminator. The days around quarter moons are the very best ones to observe the satellite with your telescope. The term "quarter moon" describes that the moon has completed one-quarter or three-quarters of its orbit, not that a quarter of the moon is lit up. Quarter moons, both first and last (or third) occur when the sun, Earth and moon form a 90-degree angle so that viewers from Earth see a half-illuminated globe.
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For that reason, full moon is not the best time to observe Earth's natural satellite with your telescope. When you observe a full moon, the sunlight is hitting it straight on, so no shadows are cast on the lunar terrain - making the moon appear less dramatic and textured. They rise as the sun sets, remain up all night and are 100 percent illuminated. Full moons happen when the moon is opposite the sun in the sky. There are numerous mobile apps, many of them free, designed to report the current phase of the moon and when the next full, new or quarter moons will occur. This is where the original concept of the "month" came from. Because the Earth is also moving around the sun at the same time, the phases of the moon actually take 29.5 days to repeat. This is why Earthlings always see the same face of the moon.Īs the moon moves around the planet, the angles among the sun, the Earth and the moon vary, producing the phases that repeat once every orbit. Due to mutual gravitational tidal forces between the Earth and moon acting over millions of years, the moon's rotation has been slowed until it equals the satellite's orbital period. The moon completes one orbit of the Earth every 27.3 days. At a mean distance of approximately 240,250 miles (384,400 kilometers), the light from the moon (which is reflected sunlight) takes 2.3 seconds to reach the Earth. The moon, also known as Luna, is Earth's nearest celestial neighbor.
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In this edition of Mobile Astronomy, we'll explore Earth's nearest natural satellite with apps that show where it is and what phase it's in (now, and in the future) apps with maps labeling the lowlands, mountains and craters apps highlighting exploration missions and even some free digital books about the moon that you can have with you at the eyepiece or just relaxing at the cottage this summer. It casts its cool glow over romantic strolls, inspires poetry, catches the eye (sometimes in broad daylight) and sends some astronomers fleeing indoors until the satellite once again departs the night sky. These are great for visual observing, but for serious astrophotography you need a mount that aligns to the celestial pole, often called a GEM, or German equatorial mount.The moon. If you move the scope up, imagine the horizon as 0 degrees and overhead as 90 degrees. North is 0 degrees, east is 90, and so on. These are easy to use and are similar to a gun mount. The other kind of mount is the Altitude and Azimuth mount. Once you set them for a known object and lock them, it’s quite easy to rotate the telescope around to an unknown object if you know its RA and DEC. These are just movable calibrated collars on the mount. If you have a telescope mount that can be aligned to the celestial north pole, you can find the object you are looking for by using setting circles. For an idea of scale, the moon is about 1/2 of a degree wide, or about 32 arc minutes when full. The celestial equator (where the line drawn from one pole to the other crosses directly overhead) has a DEC of 0 degrees. The celestial north pole has a DEC of plus-90 degrees and the south celestial pole is minus-90. Each arc minute is made up of 60 arc seconds. Each degree is comprised of 60 arc minutes. DEC is similar to latitude, but in the sky, and is listed in degrees.
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