Field of View

fov-bino   The field of view is the amount of sky you see using an optical aid. I do a lot of sky gazing using either 7×50 or 10×50 binoculars and one of the useful things to know about the binoculars is their respective field of view. In terms of degrees there is not much difference, only 1o between the 7×50 binoculars with an 8o field of view compared to the 10×50 binoculars with a 7o field of view. The greatest difference is the extra magnification the 10×50 binoculars provides.
   So how does this translate into something useful?
Star Hopping
   This is a technique for finding an object in the sky that is a known distance, in degrees, away from a more easily seen object. Typically this is done when using a telescope and the distances are the much smaller field of view for an eyepiece. Regardless of viewing with a telescope eyepiece or binoculars very often there will be a description of perhaps a faint object like an open star cluster, that is near a bright star. With a star chart you could determine which way and how many fields of view you would need to move your optical device. Then note an object across the field of view and re-aim so that the second object is now in the field of view on the side that the first object was. Repeat this until you come to the object being searched for. In this animated graphic a 7×50 binocular is used to view several Messier objects around the feet of the Gemini Twins, and the horns of Taurus the Bull by starting with the star El Nath in Taurus.
   If it Fits…
asterism-bino-ani   There are many small groupings of stars arranged in recognizable patterns like circlets, hexagons, triangles, squares, and so on. Many of these are known as asterisms, or star patterns that are not a constellation but rather are stars within one constellation making the pattern, or stars from more than one constellation sharing stars to form the asterism. Two easy to view are the ‘Y-shape’ in Aquarius the Water Bearer and the ‘Circlet’ in Pisces the Fishes.


Caution: Objects viewed with an optical aid are further than they appear.
Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

Moon and Neptune

moon-neptune   This evening, if your skies are clear take a look at the near first quarter Moon. If you have binoculars aim them at the Moon but put the bottom curve of the Moon at the upper edge of the binocular field of view. Just above the lower part of the field of view will be the near 8th magnitude planet Neptune as the banner graphic at the top of the page shows. In this simulated view I have added the apparent magnitudes of some of the stars in the general area for magnitude comparison.

   The Moon this evening, and the planet Neptune are currently located near the water vessel carried by Aquarius the Water Bearer. As the animated graphic shows Aquarius pours the water into the mouth of Piscis Austrinus, the Southern Fish. The star Fomalhaut marks the fish’s mouth.

   Take a 1 minute tour of Neptune. This is part of a longer video tour of the solar system that was part of a live performance by Dark Matter.

Caution: Objects viewed with an optical aid are further than they appear.
   Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

Follow the Arc

The ‘Evening Arc’

   There is an ‘old’ Astronomical saying, a sort of memory aid, for finding at least two constellations by way of their alpha, or brightest star in their respective constellation. In Bootes the Herdsman there is the orange-reddish star Arcturus, and in Virgo the Harvest Maiden the bluish-white star Spica. The saying – “follow the arc to Arcturus, then speed to Spica” is how you connect these two stars with the curve, or arc, in the handle of the Big Dipper. Simply look toward the north to find the 7 stars making up the Big Dipper, look for the curved handle and follow the arc or curve toward Arcturus and then continue on to Spica. This is typically done during the Northern Hemisphere spring and summer season when Bootes and Virgo are in the evening skies. However you can start this observation at sunset by looking northwest for the Big Dipper and then toward the southwest for the star Arcturus. Do this early enough as Arcturus sets about an hour after sunset and in the next couple of weeks Arcturus will become too close to the Sun and will not be visible again until later during the winter as a morning visible star.

The ‘Morning arc’

   And you could continue this observation the following morning as this part of the sky rises before the Sun and you trace out the arc passing through Arcturus and ending at Spica. As the ‘Morning Arc’ graphic shows the planet Venus is close to Spica.
   Keep an eye on this part of the sky as later this month the planets Saturn and Mercury start becoming visible before sunrise. On the 26th Venus will be very close to Saturn. As the graphic shows the two planets will be close enough for both to fit within the field of view of binoculars.

Click here to go to the Qué tal in the Current Skies web site for more observing information.