Archive for November, 2009

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Mission 12: Nova in Eridanus

November 29, 2009

Mission Objectives: Bright Stars, Constellation, Nova

Equipment: Binoculars, Telescope

Required Time: 10 minutes

Introduction: One of the cool things about this hobby is that the sky is not unchanging. Although we can’t predict when new goodies like bright comets and novae will occur, they do come around with fair regularity. Two years ago, when I was just getting into amateur astronomy, comet 17P/Holmes suddenly blew up to naked eye visibility. I just got an AstroAlert from Sky & Telescope about a nova in the constellation Eridanus, close to the bright star Rigel in Orion.

Introduction: This is one you can’t do immediately after dark. But neither will you have to stay up obscenely late or get up obscenely early. By 9:00 or 10:00 PM, Orion should be far enough above the horizon to make this a cinch.

The first step is to locate the constellation Orion. Orion is the most striking and instantly recognizable of all constellations, so it’s just a matter of looking southeast at the right time. Find the straight line of three stars between bright red Betelgeuse and even brighter Rigel, and you’ve got it. Lots of good deep sky targets in Orion, including the incomparable Great Nebula, M42, but those are missions for other evenings.

Once you’ve located Orion, you’ll have to star-hop to the nova. From Rigel, you can follow the arc of bright stars that marks the eastern end of the constellation Eridanus (green arrow). From the third star in the chain, drop down (south) to two close stars that mark the head of the stick figure shown on these charts. Alternatively, look south of Orion to find the stars that form the outline of Lepus, the Hare, and line up the stars forming the bunny’s shoulder and the top of its head to get to the stick figure’s left foot (orange arrow).

A word about these charts: they were generated by the AAVSO, or American Association of Variable Star Observers, which has a gizmo for generating finder charts for practically all of the variable stars one might want to hunt down visually. I added the colored arrows, and the stick figure is just an asterism–a chance alignment of star–that I noticed and found useful. Star hopping is subject to individual preference, so if this way of getting there doens’t work for you, generate your own finder charts and find your own way. I don’t say that to be flip or callous; sitting down with a red flashlight, some blank finder charts, and a telescope and finding (and drawing) your own asterisms is very satisfying and a great way to learn your way around the sky.

Another thing about the charts: many stars have a two or three digit number next to them. These are not identification numbers but magnitudes, so that variable star observers can determine the brightness of their target star by comparing it to other stars in the same field. Following standard practice, the decimal points are eliminated on the charts so they can’t be confused with stars. A star with the number 81 next to it shines with a magnitude of 8.1, too faint for the naked eye but within easy reach of binoculars.

Back to the stick figure. Note that stars marking the head, heart, left hand, and left foot all have close companions, which should help you distinguish them from all the other stars out there. Once you’re sure you’ve got it, find a chain of three fainter stars trending southeast from the stick figure’s left hand. Nova Eridani 2009 forms a triangle with the outermost stars in that chain. Right now it’s shining around magnitude 8.4, so it should be almost identical in brightness to the star just below it marked 81. Don’t confuse them!

Also notice that the charts are all shown with north to the top and east to the left, just as this part of the sky looks to the naked eye, binoculars, and right angle correct image (RACI) finderscopes. Straight-through finderscopes, straight-through refractors, and Newtonian reflectors will show the sky rotated by 180 degrees. No problem, just rotate the chart upside down and keep on truckin’. Refractors and cassegrain scopes using a star diagonal will show the sky rightside up, but flipped left to right. You can either flip the image ahead of time in an image-processing program, or do it mentally in your head, or–the oldest and easiest method–turn the chart over and shine a flashlight through from the other side.

So what’s going on out there? Novae are giant thermonuclear explosions that occur when a white dwarf star accumulates enough hydrogen on its surface to undergo a chain reaction. Usually the hydrogen is slurped off the surface of a companion star, perhaps a red giant. This can happen over and over again; most novae probably “go off” once every 1000 to 100,000 years, and a few like RS Ophiuchi go off every few decades.

This explosion of hydrogen on the surface of the star is in stark contrast to a Type 1a supernova, which also involves a white dwarf accreting matter from a companion. In those supernovae, the white dwarfs accumulate enough matter to approach the Chandrasekhar limit of 1.38 solar masses, at which point carbon fusion starts in their cores, followed by oxygen fusion, followed by total destabilization of the star. The star detonates in an explosion 5 billion times as bright as the sun, with a shock wave that travels at 3% of the speed of light. Neat trick, but needless to say, one that a star can only pull off once.

Fortunately for us, Nova Eridani 2009 isn’t going anywhere. However, it will dim over the coming months, so get out there and see something new.

For more info, see the Sky & Tel writeup and the AAVSO updates here, here, and here.

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Mission 11: Cassiopeia and the Double Cluster

November 21, 2009

Mission Objectives: Constellation, Open Cluster, Bright Star

Equipment: Naked eye, Binoculars, Telescope

Required Time: 3 minutes

Instructions: Go outside after dark, face northeast, and look for the sideways W. If you’re not sure which W is which, take a free sky map. The W is Cassiopeia, which lies right smack in the middle of the winter Milky Way.

Cassiopeia is a deep sky wonderland in binoculars and telescopes. There are more star clusters than you can shake a stick at–a decent portable sky atlas will show a dozen or more. Even without an atlas, it’s an awesome area to scan around in with optics of any size.

I have a confession, though. Almost every time I go out to observe in the winter, I give Cassiopeia a quick once-over and then leave. Why? Because there’s an even better pair of clusters lurking over the border of the neighboring constellation, Perseus, and Cassiopeia is such a good pointer that you might think it was put there for that purpose. Follow the inner leg of the shallow half of the W about 2/3 of the way to the next bright star, and you’ll find the Double Cluster, NGC 869 and 884. Keep in mind the effect of sky rotation–by 8:30 PM, Cassiopeia is an M centered over the North Star, and by midnight it’s a sigma to the northwest. Adjust your expectations accordingly.

The Double Cluster is one of the finest objects in the night sky, and almost always makes it onto lists with names like “Top 10 Telescopic Targets”. I’m not going to show you any pictures of the clusters themselves, because this is one place where pictures simply don’t do justice. You’ll have to get out under the night sky and see for yourself.

Once you’ve had your mind blown by the Double Cluster, keep on cruising in the same direction and follow the chain of bright stars to Mirphak, or Alpha Persei, the brightest star in the constellation Perseus. Mirphak is surrounded by a broad field of stars called the Alpha Persei association; it is too big to fit in the field of view of most telescopes (except possibly fast focal ratio, widefield scopes like the Astroscan and StarBlast 4.5), but is instead one of the best binocular targets in the entire sky. Have a look and let me know what you think.

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Mission 10: The Great Glob

November 19, 2009

Mission Objectives: Constellation, Globular cluster

Equipment: Sky map, Naked eye, Binoculars, Telescope

Required Time: 5 minutes

Related Missions: Summer Triangle

Introduction: This is a weird time of year. The classic “summer” constellations are still visible right after sunset, and by bedtime the winter constellations–especially Orion–are already coming over the eastern horizon. Of course the globe of the sky is (relatively) unchanging and you can see an angular span of the same width on any night of the year. Nothing is actually accelerated right now. It only feels odd because of the associations these stars have for me. Say “Hercules” and I think warm summer evenings and junebugs. The Pleiades, on the other hand, conjure up memories of gloves, stocking hats, and the crystaline quality of the air on a cold winter’s night. And yet you can see these things on opposite sides of the sky at the same time!

Owing to my long hiatus this fall, I let a few of the great summer objects almost get away from me. Meanwhile, a host of excellent autumn targets are high overhead even at dusk. So we’ve got no time to waste.

Instructions: Find Vega in the western sky right after sunset, and then look below it to find the back-to-back trapezoids that make up the body of Hercules. I strongly recommend taking a planisphere or sky map, such as one of the free seasonal ones here or here. If you’re like me, you can look at the map indoors, fix the points and relationships in your mind’s eye, go outside and instantly get lost. Hercules doesn’t have any first magnitude stars to help you orient, and there are far too many medium-brightness stars, so the number of possible trapezoids you can construct is large. This is where the directions I can give break down; there is just no substitute for having the map in your hand, especially since the free ones are so good these days. See how many of the stars west of Vega you can see with the naked eye, and then draw a trail that will guide you from Vega down to where you need to go. The path you find will be the one that makes the most sense to you.

You’ll know for sure when you’ve got the right trapezoids, because 2/3 of the way along the western edge of the northern trapezoid is a fuzzy ball. This is M13, the Great Globular Cluster in Hercules. If you are under super dark skies you might just make it out with the naked eye as a dim and blurry star. Under all but the worst city lights, you can sweep between the two boundary stars and pick it up in binoculars. In 10x50s it is an attractive ball of fuzz, and in 15x70s it is a slightly larger, brighter, and more appealing ball of fuzz. In a small telescope some of M13’s 100,000 stars start to resolve, like a spill of very fine sugar on black velvet. In a big telescope, like my friend’s 16-incher, it is almost overwhelming; the eyepiece is so full of stars that it gets to be too much for the eye–and the mind–to take in. I found myself repeatedly looking away to give myself a break. That’s good stargazing.

Like M22 in Sagittarius and all other known globular clusters, M13 is old, and I mean old even for astronomy, where a five-billion-year-old star like the sun is something of a youngster. Even if all you have to see it with is binoculars, there is something special about tickling your retinas with the light of 100,000 twelve-billion-year-old suns.

Photo from APOD.

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Mission 9: The Mote in God’s Eye

November 17, 2009

Mission Objectives: Bright star, Exoplanet

Equipment: Naked eye

Required Time: 1 minute

Related Missions: Hail to the King

Instructions: Go outside after sunset, face south, and find Jupiter. South and east (or down and left) of Jupiter is a bright star called Fomalhaut. Fomalhaut is the only bright star in that part of the sky, so there’s little chance you’ll confuse it with anything else. It’s not a double star, doesn’t have a striking color, and isn’t part of a striking pattern (it’s also pretty far south, at roughly the same elevation as Sagittarius, so if you’re at high latitudes, good luck). Its attractions are entirely cerebral.

Fomalhaut is special because it has an extrasolar planet, Fomalhaut b, which was the first extrasolar planet to be imaged directly by an optical telescope. What’s all that mean? People had been detecting extrasolar planets for years, by measuring the wobble they induced in their parent stars, or measuring the light drop in their parent stars as the exoplanets pass in front of them, and the spectra of exoplanets had even been obtained, but Fomalhaut b was the first to have its picture taken. The Hubble image itself is cool; it looks like the Eye of Sauron.

Now, as of this writing 405 explanets have been found, with more coming almost every month, especially now that the Kepler telescope is up and running. But most of these orbit stars that are very dim as seen from Earth. Fomalhaut rocks because it’s obvious. You can point it out to someone and say, “That star has a planet, and we have taken pictures of it.”

Hubble image at top from NASA, artist’s reconstruction above from the Joint Astronomy Centre. Apologies to Niven and Pournelle for nicking their title.

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Al-most the-ere

November 15, 2009

s-trench1

Well, I did get out of bed this morning and catch the very, very old crescent moon. It was just a white sliver hanging in the sky below Venus, like the very edge of a cosmic thumbnail.

One more to go: the waxing crescent moon within 40 hours of new. Tomorrow night will be too soon, and Wednesday night will be too late, so if I’m going to finish the Lunar Club this month, Tuesday is my only hope. If there are clouds to the west, or if the vast stew of atmospheric sludge over LA is too dense, I’ll be thwarted.

Fingers firmly crossed.

Waning gibbous moon in 15x70s

The waning gibbous moon from a little over a week ago, photographed through my 15x70 binoculars.

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Dawn patrol

November 14, 2009

Dawn patrol 2009-11-14

So I’m trying to finish up this Astronomical League observing club. Not the Galileo Club, although I am persevering with tracking Jupiter’s moons and all the rest. No, I’m talking about the Lunar Club, a list of 100 targets for the naked eye, binoculars, and telescopes.

I’ve been chipping away at it off and on for over a year, and I’ve been stuck on the last three targets for months. Ironically, it’s not tiny detailed features that are holding me up, but naked-eye views of the whole disk. The clincher isn’t size or distance, but time. Specifically, get-out-of-bed time. My last few targets are views of very thin crescent moons, mostly waning crescent moons that are only briefly visible before sunrise.

I’m a night-owl, not  a morning person. If I’m up at 5:00 AM, it’s usually because I stayed up, not because I got up. But this morning I dragged my carcass out of bed at that unholy hour to go out and see “the new moon in the old moon’s arms”. That enchanting term refers to the faint illumination of the moon’s disk lit by Earthlight, between the much brighter horns” of the crescent that are still lit directly by sunlight.

You’ll recall that near new moon, the moon is between the Earth and sun, and the far side is almost fully illuminated and the near side is almost fully in shadow. At one time or another you probably have seen a young crescent moon low in the western sky at sunset, with the entire disk visible. That’s the flip side, after new moon, “the old moon in the new moon’s arms”. The photo on the right side of my banner is a one-second exposure of this phenomenon, taken with my Nikon Coolpix 4500 and 6-inch reflector. It’s really striking how many features you can make out on the shadowed disk by the faint reflected Earthlight, especially with a telescope.

My last three Lunar Club observations are:

  • New Moon in Old Moon’s Arms (Within 72 hrs of new)
  • Crescent Moon, Waning (Within 48 hrs of new)
  • Crescent Moon, Waxing (Within 40 hrs of new)

There’s also one about seeing the old moon in the new moon’s arms within 72 hours of new, but you can see that any month without really trying so I knocked it off ages ago.

New moon is Monday at 11:14 AM PST, so the 72 hour window opened yesterday at 11:14 AM. This morning I saw the new moon in the old moon’s arms. Tomorrow morning–assuming I get out of bed and there aren’t any clouds–I will hopefully see the waning crescent within 48 hours of new. Then Tuesday evening I’ll have a chance to catch the waxing crescent within 40 hours of new, and thus complete the requirements for the Lunar Club.

C’mon, alarm clock!

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Mission 8: Neptune

November 11, 2009

Mission Objective: Planet

Equipment: Binoculars, Telescope

Required Time: 2 minutes

Related Missions: Hail to the King, AL Galileo Club

Instructions: Find Jupiter in the southern sky. About three degrees to the left are two bright stars in a row, part of the group of stars that mark the northeast corner of the constellation Capricorn (if you’re not familiar with Capricorn, look it up in Stellarium or on this month’s free sky map). Just above the farther and  brighter of the two stars, and forming a right triangle with them, is a cross- or X-shaped group. The three middle stars are the brightest, the one on the lower right is dimmer, and the one on the upper left is Neptune (remember that left and right are almost always reversed in a telescope, and often up and down as well). Once you’ve found it, you’re all done with task #12 in the Astronomical League’s Galileo Club.

Jupiter and Neptune in Stellarium

Neptune has one of the oddest discovery stories of any celestial object. Galileo spotted it twice but didn’t recognize it for what it was–which is perhaps excusable, since he was busy discovering almost everything in the solar system with a one-inch telescope. In the early 1800s, astronomers in France and England realized that anomalies in the orbit of Uranus pointed to the presence of another planet beyond. In the 1840s both John Couch Adams in England, and Urbain Le Verrier in France, calculated the position of the then-hypothetical eighth planet. Adams’ calculations were first, Le Verrier’s were better, but neither man had much success stirring up interest in a telescopic search for the planet. James Challis at the Cambridge Observatory did take up the search, but not with any enthusiasm.

Le Verrier eventually wrote to Johann Galle, director of the Berlin observatory, to urge him to search for the planet. The very evening that he received the letter, Galle found the eighth planet, about one degree from where Le Verrier had predicted, and about 12 degrees from where Adams had predicted. Challis later realized that he had observed Neptune not once, but twice, before Galle, but didn’t recognize it as a planet, basically because he wasn’t paying attention. Challis is mainly remembered today as the man who almost discovered Neptune.

Le Verrier first proposed the name Neptune, but then changed his mind and argued forcefully that the new planet should be named…Le Verrier. This act of literally cosmic arrogance was widely supported in France (naturellement) and widely detested everywhere else. The earlier name stuck.

Neptune is 2.8 billion miles out from the Sun, more than five times farther than Jupiter, and 30 times farther than Earth. The solar system makes a lot more sense when we recognize Neptune, and not Pluto, as the most distant of the true planets: there are four rocky worlds, then a belt of rocky crap from back in the day, then four gas giants, then several associations of icy crap from back in the day, from the Kuiper Belt out to the Oort Cloud. Pluto is just one of many, many icy worldlets in the distant reaches of the solar system, and not even the biggest. The last picture here nails it, and the whole thing is worth reading.

Anyway: 2.8 billion miles. Go have a look, and give that some thought.