BINOCULARS:
Why You Need a Pair
Of all of the accessories carried by the modern amateur astronomer, by far the most useful has to be binoculars. There are a number of reasons why they're the go-to item in every amateur astronomer's toolbox.
One of the first reasons is that binoculars offer stereo vision. Unlike when squinting through a telescope, both of your eyes are engaged. For most people, it's easier to see that way.
Second up, and right behind, is the fact that binoculars are a 'point and shoot' type of product. You want to see what's over there? Then point the binos at it. It's that simple.
Third, binoculars offer a wide field of view and generally good light-gathering characteristics. Surprisingly enough, many astronomical objects cannot be seen by the naked eye because they are too faint, not too small. Binoculars make a vast collection of objects accessible.
With binoculars, you can rapidly sweep a portion of the sky for interesting sights. You'll spot a lot of clumps of stars; you might see a couple of planets; and there are plenty of faint fuzzies within the reach of binoculars.
Binoculars are a great way to familiarize yourself with the night sky. They bring so much into visual range; for example, nearly all of the "faint fuzzies" mentioned last week look fantastic in binos.
In terms of what to look for, you'll want a pair of 7x50s or 10x50s. (The first number refers to the image-multiplying power; the second refers to diameter of each objective lens, in millimetres.)
If your hands shake a bit, go for the lower power. It's not worth trying to get a consistent view through 10x50s.
If you get yourself binoculars, also get a good star chart of some description. Most show all of the brightest stars, and a fair number of faint fuzzies to get you started.
For a flashlight, might I suggest you go with red. Red light interferes less with the night vision you pick up in dark surroundings. That becomes more important when you're dark-adapted, believe me.
When I go out to observe, even with a telescope, I keep my binos within easy reach.
You don't have to spend much; even a cheap pair is better than nothing. Avoid plastic lenses; they suck. Most decent binoculars have glass lenses.
Once you get a pair of binoculars, use them to familiarize yourself with the night sky. There's plenty to see, especially in a dark sky. Try to minimize sources of glare--streetlights, domestic and industrial lighting, etc.
A word to the wise: in densely-populated areas, standing outside with a pair of binoculars is sure to arouse suspicion. People just imagine the worst, and they just know you're spying on them. You may need to seek a location from which you can observe undisturbed.
When you get a pair of binoculars, first make sure you're using them the right way round. The big lenses go in the front, and you look through the little ones--and it's amazing how often Hollywood gets that simple fact wrong!
There are two extremely-valuable adjustments to be made to a pair of binoculars. First off, the spacing between the lenses can be varied, to match the spacing between your eyes. Looking through them, you should see two overlapping circles, and any objects should be converged, if not actually in focus.
Second, most binos have an independent focuser for the right eyepiece (because most people's eyes are just a bit different). The idea is to use the tilt bar on top to achieve sharp focus in the left eye; then use the adjustment to get matching results in the right eye. Generally, you need only rotate the eyepiece to use this feature.
The nicest thing about binoculars is that they are compact and can go anywhere. They last forever (I've got a pair that's twenty years old; they'll be good for another thirty to fifty years; probably they'll outlast me.)
Binoculars: an essential piece of kit.
Friday 28 December 2018
Thursday 20 December 2018
Faint Fuzzies
In the night sky, the vast majority of the objects you can see with the naked eye are stars, many of them larger and brighter than our own sun.
But, scattered here and there, you can find a few objects that are neither stars nor planets. These are faint objects, best seen in a dark country sky. Hey, that's just the way it is. We've polluted our urban skies to the point where only the brightest stars can be seen.
Here, then, is a brief tour of some of the most-prominent of these "faint fuzzies."
For all of these, it will help to have star charts, or a planetarium program on your phone/tablet. I'm not doing up charts for a blog post.
Mizar and Alcor
Okay, technically, it's not a star, per se—it's two stars. Mizar and Alcor, situated at the bend in the handle of the Big Dipper asterism, can be seen by most people with normal vision as a double star. The bright one is Mizar; the dimmer one is Alcor. Native Americans used to refer to this pair as the "horse and rider."
The Andromeda Galaxy
This is one of the most-distant objects the naked eye can pick out of the sky, at approximately 2.4-million light-years. It is located in the constellation Andromeda (nothing to do with the High Guard, or Captain Hercules), which itself is off the left 'shoulder' of the great Square of Pegasus.
In a dark sky, and using averted vision (looking slightly away from the object, to engage the more light-sensitive rods in our eyes), a fuzzy area up to a degree in diameter (about twice the width of the Full Moon) can be perceived. In binoculars, this object gently glows like a desk lamp. If nothing else, learning to point out Andromeda can make you a hero to your friends (or a total nerd; you have been warned).
The Double Cluster
Hanging in the polar sky, partway between with cosmic 'W' of Cassiopeia and the hydra-like form of Perseus, is the double cluster--two clusters of stars. With the naked eye, one perceives a fuzzy patch, about half the width of the Full Moon. In binoculars, some of the stars in each cluster begin to resolve, giving you a view of two piles of diamond chips, set upon crushed velvet.
The Centaurus Cluster
This is a great globular cluster of stars. Globulars orbit the galaxy; most of them are much further away. The Centaurus cluster shows as a fuzzy patch. In binoculars, it shows up as a larger, brighter fuzzy patch. The reason? It is composed of over a million stars, at a considerable distance.
The Pleiades
This open cluster sits just to the left (east) of the horns of Taurus (itself another open cluster, only closer to us, and less dense). Normally-sighted people can generally perceive six to eight stars in a compact grouping. Some will comment on its dipper-like appearance.
The Great Orion Nebula
This is a huge cloud of gas and dust, including many star-forming regions, in the constellation Orion. Orion itself is prominent in the winter and spring skies as a large X with three stars in the middle. Tracing down slightly from that point, one finds three more stars (the Dagger). One of those stars is fuzzy. It looks magnificent in binoculars or a telescope.
The Northern Coalsack
Thus far, each of the objects described can be detected from the light it emits. This one, on the other hand, can be detected for the light it blocks. The Northern Coalsack, in the Contellation Cygnus, is a large darkening in the middle of the gently-glowing band of the Milky Way.
The Milky Way
It's sad that only a fraction of the population today has seen the Milky Way. It's a grand spectacle in a dark sky; a band of luminescence that shines from pole to pole. It's our own galaxy, and the light you are seeing is from billions of stars, at distances to great for them to be resolved.
This pretty much concludes our tour of faint fuzzies. Next time you find yourself in a dark sky, try looking for a few of them.
-Bill
In the night sky, the vast majority of the objects you can see with the naked eye are stars, many of them larger and brighter than our own sun.
But, scattered here and there, you can find a few objects that are neither stars nor planets. These are faint objects, best seen in a dark country sky. Hey, that's just the way it is. We've polluted our urban skies to the point where only the brightest stars can be seen.
Here, then, is a brief tour of some of the most-prominent of these "faint fuzzies."
For all of these, it will help to have star charts, or a planetarium program on your phone/tablet. I'm not doing up charts for a blog post.
Mizar and Alcor
Okay, technically, it's not a star, per se—it's two stars. Mizar and Alcor, situated at the bend in the handle of the Big Dipper asterism, can be seen by most people with normal vision as a double star. The bright one is Mizar; the dimmer one is Alcor. Native Americans used to refer to this pair as the "horse and rider."
The Andromeda Galaxy
This is one of the most-distant objects the naked eye can pick out of the sky, at approximately 2.4-million light-years. It is located in the constellation Andromeda (nothing to do with the High Guard, or Captain Hercules), which itself is off the left 'shoulder' of the great Square of Pegasus.
In a dark sky, and using averted vision (looking slightly away from the object, to engage the more light-sensitive rods in our eyes), a fuzzy area up to a degree in diameter (about twice the width of the Full Moon) can be perceived. In binoculars, this object gently glows like a desk lamp. If nothing else, learning to point out Andromeda can make you a hero to your friends (or a total nerd; you have been warned).
The Double Cluster
Hanging in the polar sky, partway between with cosmic 'W' of Cassiopeia and the hydra-like form of Perseus, is the double cluster--two clusters of stars. With the naked eye, one perceives a fuzzy patch, about half the width of the Full Moon. In binoculars, some of the stars in each cluster begin to resolve, giving you a view of two piles of diamond chips, set upon crushed velvet.
The Centaurus Cluster
This is a great globular cluster of stars. Globulars orbit the galaxy; most of them are much further away. The Centaurus cluster shows as a fuzzy patch. In binoculars, it shows up as a larger, brighter fuzzy patch. The reason? It is composed of over a million stars, at a considerable distance.
The Pleiades
This open cluster sits just to the left (east) of the horns of Taurus (itself another open cluster, only closer to us, and less dense). Normally-sighted people can generally perceive six to eight stars in a compact grouping. Some will comment on its dipper-like appearance.
The Great Orion Nebula
This is a huge cloud of gas and dust, including many star-forming regions, in the constellation Orion. Orion itself is prominent in the winter and spring skies as a large X with three stars in the middle. Tracing down slightly from that point, one finds three more stars (the Dagger). One of those stars is fuzzy. It looks magnificent in binoculars or a telescope.
The Northern Coalsack
Thus far, each of the objects described can be detected from the light it emits. This one, on the other hand, can be detected for the light it blocks. The Northern Coalsack, in the Contellation Cygnus, is a large darkening in the middle of the gently-glowing band of the Milky Way.
The Milky Way
It's sad that only a fraction of the population today has seen the Milky Way. It's a grand spectacle in a dark sky; a band of luminescence that shines from pole to pole. It's our own galaxy, and the light you are seeing is from billions of stars, at distances to great for them to be resolved.
This pretty much concludes our tour of faint fuzzies. Next time you find yourself in a dark sky, try looking for a few of them.
-Bill
Friday 14 December 2018
Perihelion - What's it All About?
At this time of year, Earth is rapidly approaching perihelion--its point of closest approach to the sun. This is a consequence of Earth's orbit being elliptical, not circular.
Take a look at this diagram:
In the above diagram, the Earth is a blue ball; the Sun is a yellow ball. Earth is travelling in the counter-clockwise direction. As you can see, we're rapidly approaching the point of closest approach (A). The opposite point, aphelion, is at point (B). The Vernal Equinox, which marks the first day of spring, is at (C); and the autumnal equinox, marking the first day of fall, is at (D).
Now, interestingly enough, the speed at which our planet moves is inversely proportional to its distance from the sun (I know that's not quite true; but it will suffice for now). Right now, our planet is moving faster than usual. This has consequences.
The first consequence is that the planet spends less time between the autumnal and vernal equinoxes (the left-hand side of the image), and more time between the vernal and autumnal equinoxes. You can confirm this by counting the days between the two equinoxes. Now, Earth's orbital eccentricity is small, and so is the effect; but it's there.
This also has the effect of advancing the equation of time (basically put, the difference between the actual time, and the time a sundial would tell you). Right now, Earth is moving faster than usual; this has the effect of pushing both sunrise and sunset 'backward.' And so the equation of time is increasing in the negative direction (you'd have to subtract from the sundial time). Around the vernal equinox, this situation will reverse itself.
A related consequence is that, while the longest and shortest days of the year remain on the solstices, the dates of earliest and latest sunrise and sunset are offset. We've already passed our earliest sunset of the year, for example; but sunrise will continue to get later into late December/early January.
One other consequence to be noted, here: because perihelion falls shortly after the southern solstice (winter in the Northern Hemisphere), Southern-Hemispheric summers are slightly warmer, and the winters slightly colder.
That's enough for now.
-Bill
At this time of year, Earth is rapidly approaching perihelion--its point of closest approach to the sun. This is a consequence of Earth's orbit being elliptical, not circular.
Take a look at this diagram:
In the above diagram, the Earth is a blue ball; the Sun is a yellow ball. Earth is travelling in the counter-clockwise direction. As you can see, we're rapidly approaching the point of closest approach (A). The opposite point, aphelion, is at point (B). The Vernal Equinox, which marks the first day of spring, is at (C); and the autumnal equinox, marking the first day of fall, is at (D).
Now, interestingly enough, the speed at which our planet moves is inversely proportional to its distance from the sun (I know that's not quite true; but it will suffice for now). Right now, our planet is moving faster than usual. This has consequences.
The first consequence is that the planet spends less time between the autumnal and vernal equinoxes (the left-hand side of the image), and more time between the vernal and autumnal equinoxes. You can confirm this by counting the days between the two equinoxes. Now, Earth's orbital eccentricity is small, and so is the effect; but it's there.
This also has the effect of advancing the equation of time (basically put, the difference between the actual time, and the time a sundial would tell you). Right now, Earth is moving faster than usual; this has the effect of pushing both sunrise and sunset 'backward.' And so the equation of time is increasing in the negative direction (you'd have to subtract from the sundial time). Around the vernal equinox, this situation will reverse itself.
A related consequence is that, while the longest and shortest days of the year remain on the solstices, the dates of earliest and latest sunrise and sunset are offset. We've already passed our earliest sunset of the year, for example; but sunrise will continue to get later into late December/early January.
One other consequence to be noted, here: because perihelion falls shortly after the southern solstice (winter in the Northern Hemisphere), Southern-Hemispheric summers are slightly warmer, and the winters slightly colder.
That's enough for now.
-Bill
Tuesday 11 December 2018
The Sky for December 2018
This is the start of a new feature of my blog, whereby I share my astronomical knowledge, accumulated through 45 years, plus about 20 of observational astronomy.
In the sky this month, there are a few things to catch your attention. Let's focus on those.
Earth's Shadow
This is often noticed in December, when sunrise and sunset often coincide with our morning or evening commute. It happens shortly before sunrise, and shortly after sunset, on clear days.
What you notice is, near the anti-sunrise/set point (opposite from where the sun is about to rise or has just set), a darker slice of atmosphere hugging the horizon. As sunrise approaches, it seems to concentrate right above the horizon. As more time passes after sunset, the band rises higher and dilutes.
What you're seeing is the Earth's shadow, cutting up through our atmosphere. Very near to sunrise or sunset, this is a very slight angle, so you're looking 'straight down' the shadow; and thus it seems quite dark. Further away from either time, The angle is less shallow (the shadow is angled more), and the effect fades.
Venus
In December mornings, before sunrise, a bright, star-like object can be seen rising into the sky in the Southeast. It's brighter than virtually anything else in the sky, save for the Sun and the Moon, and shines with a steady, untwinkling light.
What you're looking at is Venus, Often referred to as Earth's sister planet. This is because both its diameter is just a few-hundred kilometres smaller than Earth's, and also because of its proximity to our own orbit around the sun (Venus, average distance about 108-million km; Earth, average distance about 149-million km).
On closer examination, though, the claim of sisterhood falls apart, A thick, carbon-dioxide atmosphere cloaks the planet, smothering the surface under its crushing weight. Surface temperatures are hot enough to melt lead. What's more, Venus actually rotates retrograde (against its orbit, so to speak), and its day (243 earth days) is actually longer than its year (277 days).
The Soviets soft-landed a spacecraft on Venus, in the mid-1970s; surface photos were recovered.
Incidentally, Venus, like most of the planets, doesn't twinkle. That's because, while tiny, the disks they display tend to be larger than the turbulence cells in the upper atmosphere that cause twinkling; thus, the cells mostly cancel each other out, and no twinkling.
Sirius
Rising in the Southeast late in the evening is Sirius, once known as the Dog Star. Sirius gets its nickname by virtue of being the brightest star in the constellation Canis Major (the Great Dog). It's a bit larger and brighter than the sun, and it has a companion--Sirius B, a white dwarf (a star that has used up all of its nuclear fuel and, because of its relatively small mass, died a quiet death).
I mention Sirius B because the Dogon Tribe, in Africa, holds a festival once every so often to commemorate Sirius B's orbit. The catch: Sirius B is much too faint, and too close to Sirius A, to be seen by the naked eye.
Canis Major, Sirius' home constellation, is one of several companions to great Orion, the Hunter. (Two others are Canis Minor (the Lesser Dog), with its bright star Procyon; and Taurus (the Bull), and its bright red-giant star, Antares.
Sirius twinkles madly, most nights, and seems to display most of the colours of the rainbow. That's because it is, through atmospheric refraction. Other stars do it, too—they're just not bright enough for you to notice.
Orion
In my childhood, I was often stopped in my tracks by the sight of a large X in the Spring sky. After not too many years, I learned that it was Orion, the Hunter. You've probably seen it; a large X, with four bright stars prominently marking the corners, and three fainter stars in the middle. Well, that's Orion. The three stars in the middle are called the Belt. Three further stars 'hang down' from the belt; this is the Dagger.
Now, a curious thing is the Dagger. In a clear, country sky, you can notice with the naked eye that one of the stars in the Dagger is fuzzy. And, indeed, binocular or telescopic aid will reveal that you are looking at a huge, interstellar gas cloud.
What you are looking at is the Great Orion Nebula, the subject of so many telescopic portraits over the years. You've doubtless seen Hubble images of the many gas/dust 'coccoons' inside which new stars and planets are forming.
Those are the major sights for which to keep an eye out over the next month. Some other events (in brief): earliest sunset (mid-latitude) Dec. 11; Winter, or Southern, Solstice Dec. 20.
That's it for this month. If you don't have a good pair of binoculars, do invest.
-Bill
This is the start of a new feature of my blog, whereby I share my astronomical knowledge, accumulated through 45 years, plus about 20 of observational astronomy.
In the sky this month, there are a few things to catch your attention. Let's focus on those.
Earth's Shadow
This is often noticed in December, when sunrise and sunset often coincide with our morning or evening commute. It happens shortly before sunrise, and shortly after sunset, on clear days.
What you notice is, near the anti-sunrise/set point (opposite from where the sun is about to rise or has just set), a darker slice of atmosphere hugging the horizon. As sunrise approaches, it seems to concentrate right above the horizon. As more time passes after sunset, the band rises higher and dilutes.
What you're seeing is the Earth's shadow, cutting up through our atmosphere. Very near to sunrise or sunset, this is a very slight angle, so you're looking 'straight down' the shadow; and thus it seems quite dark. Further away from either time, The angle is less shallow (the shadow is angled more), and the effect fades.
Venus
In December mornings, before sunrise, a bright, star-like object can be seen rising into the sky in the Southeast. It's brighter than virtually anything else in the sky, save for the Sun and the Moon, and shines with a steady, untwinkling light.
What you're looking at is Venus, Often referred to as Earth's sister planet. This is because both its diameter is just a few-hundred kilometres smaller than Earth's, and also because of its proximity to our own orbit around the sun (Venus, average distance about 108-million km; Earth, average distance about 149-million km).
On closer examination, though, the claim of sisterhood falls apart, A thick, carbon-dioxide atmosphere cloaks the planet, smothering the surface under its crushing weight. Surface temperatures are hot enough to melt lead. What's more, Venus actually rotates retrograde (against its orbit, so to speak), and its day (243 earth days) is actually longer than its year (277 days).
The Soviets soft-landed a spacecraft on Venus, in the mid-1970s; surface photos were recovered.
Incidentally, Venus, like most of the planets, doesn't twinkle. That's because, while tiny, the disks they display tend to be larger than the turbulence cells in the upper atmosphere that cause twinkling; thus, the cells mostly cancel each other out, and no twinkling.
Sirius
Rising in the Southeast late in the evening is Sirius, once known as the Dog Star. Sirius gets its nickname by virtue of being the brightest star in the constellation Canis Major (the Great Dog). It's a bit larger and brighter than the sun, and it has a companion--Sirius B, a white dwarf (a star that has used up all of its nuclear fuel and, because of its relatively small mass, died a quiet death).
I mention Sirius B because the Dogon Tribe, in Africa, holds a festival once every so often to commemorate Sirius B's orbit. The catch: Sirius B is much too faint, and too close to Sirius A, to be seen by the naked eye.
Canis Major, Sirius' home constellation, is one of several companions to great Orion, the Hunter. (Two others are Canis Minor (the Lesser Dog), with its bright star Procyon; and Taurus (the Bull), and its bright red-giant star, Antares.
Sirius twinkles madly, most nights, and seems to display most of the colours of the rainbow. That's because it is, through atmospheric refraction. Other stars do it, too—they're just not bright enough for you to notice.
Orion
In my childhood, I was often stopped in my tracks by the sight of a large X in the Spring sky. After not too many years, I learned that it was Orion, the Hunter. You've probably seen it; a large X, with four bright stars prominently marking the corners, and three fainter stars in the middle. Well, that's Orion. The three stars in the middle are called the Belt. Three further stars 'hang down' from the belt; this is the Dagger.
Now, a curious thing is the Dagger. In a clear, country sky, you can notice with the naked eye that one of the stars in the Dagger is fuzzy. And, indeed, binocular or telescopic aid will reveal that you are looking at a huge, interstellar gas cloud.
What you are looking at is the Great Orion Nebula, the subject of so many telescopic portraits over the years. You've doubtless seen Hubble images of the many gas/dust 'coccoons' inside which new stars and planets are forming.
Those are the major sights for which to keep an eye out over the next month. Some other events (in brief): earliest sunset (mid-latitude) Dec. 11; Winter, or Southern, Solstice Dec. 20.
That's it for this month. If you don't have a good pair of binoculars, do invest.
-Bill
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