Archive for the ‘Bright stars’ Category

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Mt Wilson: even better the second time around

June 14, 2010

About a dozen of us from the Pomona Valley Amateur Astronomers spent Saturday night observing with the 60-inch telescope up on Mount Wilson. A really excellent night on the mountain is a Goldilocks affair–you need enough of a marine layer to cover up the lights of LA, but the fog has to stay low enough not to swamp the observatory itself. The PVAA visited Mount Wilson last summer, but got fogged out. That worked out okay for me, because they rescheduled for the fall and I found out about the trip in time to go along.

Saturday night the marine layer was looking  pretty good when we got there. Unfortunately, it cleared out before midnight, so the sky was too bright for us to do any serious galaxy observing. But we saw quite a few planetary nebulae and globular clusters, which punch through the light pollution better than most galaxies.

We saw a lot of burnt trees on the way in, from last fall’s Station Fire, which at one point threatened the observatory. The trees by the gate had some light charring down near the bottoms of their trunks, but they hadn’t burned very high or very hot, and I suspect that the fire evidence I saw there was caused by backfires set by the firefighters who saved the observatory.

The 60-inch telescope, largest in the world from 1908 to 1917, is as impressive as ever.

Our first target was Saturn. Although the seeing settled down later in the evening, right after dark the sky was pretty turbulent and that cut down on the amount of detail we could see. Also, and to my immense irritation, I couldn’t get my camera to focus with the optical zoom engaged, so I couldn’t  increase the object size on the CCD as much as I would have liked. This photo doesn’t really do the view justice–in fact, it’s not much better than I’ve done with my 10-inch scope from my driveway (proof here).  Remember that this is a sad comment on the state of the just-past-sunset atmosphere and my finicky camera, and not a slight on the telescope, which is capable of much better!

But things did get better as the evening progressed and we saw tons of cool stuff. Several other people were experimenting with their own digital cameras and that inspired me to try some things I haven’t done before, like photographing double stars. Here is Albireo, a summer favorite that is easily split by even small telescopes.

We started with Saturn and ended with Jupiter; the King of the Planets was climbing in the east as the sky started to brighten before dawn. If you haven’t looked at Jupiter in a while, the Red Spot is actually red again, and the normally-brown South Equatorial Belt has faded almost completely. This is a big switch from the past year or two, when the “Red” Spot has mostly been visible as a white notch in the SEB. It was far and away the best look at the GRS that I’d ever gotten.

The highlight of the evening for me was seeing M13, the Great Globular Cluster in Hercules, and M5, another excellent summer glob, back to back. M13 is probably in most deep sky observers’ top ten, but some people like M5 better, and I’m in that camp. M5 isn’t quite as big or bright, although it comes very close, but it has a much more compact core and the outer stars are arranged in loops and swirls rather than radiating chains. To my eyes, M5 looks like an explosion of stars, in progress. It’s good in my ten-inch scope. It’s phenomenal in the 60-inch.

Last fall we went on a weeknight and I had to leave early, around 3:00 AM or so, to get up to teach the next morning. We also had a considerably larger group, so we didn’t get through as many objects per unit time. Obviously going with a big group is better for the club, but it was nice to have a more intimate group and a shorter line at the eyepiece. I had a heck of a good time, and I plan on going back up every chance I get. If it’s within your means, you should do likewise.

Many thanks to our host and telescope operator for another tremendous evening!

Update: I’m kind of a doofus. If you were wondering why this post is included in the binocular category, it’s because I took my 15×70 bins with me and did some deep-sky observing out of the opening in the dome, while waiting in line for the eyepiece. I bagged four targets for the AL Deep Sky Binocular club, which leaves me with only six more needed to complete that list. But I forgot to mention all of this when I first posted!

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Mission 18: Diamonds from the Ring of Fire

February 27, 2010

Mission Objectives: Bright stars, Open clusters, Messier objects, Star hopping

Equipment: Sky map, Binoculars, Telescope

Required Time: 5-10 minutes per window

Related Missions: Ring of Fire

Introduction: Here on Earth, diamonds are found in the magma pipes that fed long-extinct volcanoes. Sometime in the distant future, the volcanic provinces of the Pacific “Ring of Fire” will be prime diamond-hunting territory. So it’s fitting that winter’s Ring of Fire is also full of diamonds, in the form of open clusters that decorate the winter Milky Way.

All of the clusters described here are within reach of 50mm binoculars, although most won’t show much detail at 7-10x. Even the smaller ones will start to differentiate in 15×70 binoculars, and all of them are stunning in telescopes of any size.

Instructions for M41, M93, M46 and M47: Go outside after dark, face south, and find Sirius. Use it to trace the “doggy” shape of Canis Major. M41 is the biggest and brightest of the clusters in this area, and it’s an easy catch right in the heart of the dog. I usually find it by centering Sirius in the field of view and then just sweeping down (south) through the constellation. It never fails to swim into view. If you’re having a hard time, M41 makes one corner of an elongated triangle with Sirius and a trio of brightish stars along the dog’s back.

After M41, the rest of the Messier clusters around Canis Major may seem a bit anticlimactic, but each has its own charm and they are all well worth tracking down. And there are even better clusters to come.

Although it is nowhere near as brilliant as M41, M93 is one of my favorites. It is small but fairly dense, and at low magnification its irregular shape makes me think of a silvery flame burning in the night sky. To get there, trace your way down the dog’s back to the bright stars Wezen, Adhara, and Aludra, which mark the dog’s hindquarters and tail. If you’re in doubt about which is which, note that these three stars form a right triangle with Aludra at the south end. From Aludra, a loose chain of bright stars trails east into the constellation Puppis. Sweep over and up, over and up, and you’ll see M93. If you get to a star as bright as Aludra, you’ve hit Rho Puppis (looks like ‘p Pup’ in the map above) and gone too far.

The last two in this window, M46 and M47, make a nice contrasting pair. From Sirius, scan east to find the stars that make the back of the dog’s head. I imagine these stars forming one end of a shallow arc that includes several bright background stars and ends on the paired clusters. If that doesn’t work for you, use Stellarium or the atlas of your choice to pick out intermediate stars to use as waypoints. A word of caution: this is a rich region of the sky, with loads of tiny faint clusters that aren’t marked on any but the most detailed maps. More than once I have been looking for M46 and M47 and gotten hung up in the wrong place. If you have any doubt about whether the clusters you’re looking at are the right ones, they’re probably not. One way to recognize them for sure is to note the differences between them; M47 is very sparse with a handful of bright stars in an irregular pattern, whereas M46 has many more stars that are more even in brightness, although none of them are nearly as bright as the most prominent members of M47.

Instructions for M35-M38: Now go to the north end of the Ring of Fire, to the bright star Capella. Use it to trace the 5- or 6-sided (depending on how many stars you include) ring of the constellation Auriga. The side of the polygon opposite Capella is formed by the long line from Alnath (technically in the neighboring constellation Taurus) to the next star clockwise. The clusters M37 and M36 are on either side of that line at the halfway point. Extend the line from M37 to M36 on to the west with a slight bend to the north to find M38. As with M46 and M47, this trio of clusters make an interesting study in contrasts. Here are my notes from Messier Marathon night:

  • M37: compact, dense with faint stars, very rich but dim
  • M36: smallest but brightest of trio, dominated by a few brighter stars
  • M38: intermediate between the other two in both richness and brightness

The first time I observed these clusters, I found M37 and M36 easily and then spent almost an hour trying to locate M38. It just wasn’t there! Then I checked the descriptions of the clusters and realized that I had actually been looking at M36 and M38. I’d been extending the line in the wrong direction. I backtracked and picked up M37 easily–an illustration of why it is useful to know what things ought to look like, and not just where they are.

The Auriga trio are nice clusters, but the fourth and final M-cluster in this window blows them all away. To find M35, trace down the body of the western twin in Gemini, from bright Castor to the swooping arc of stars that marks the outside ‘foot’. Just above the toe of the boot, in a right triangle with the last two stars in the arc, you’ll find M35, a big, bright cluster that rivals M41 in either binoculars or telescopes. If you’ve got a telescope, you can get a twofer–the small, compact cluster NGC 2158 is right next to M35 in the same field. It’s a tough catch in binoculars unless you’re under dark skies, but almost any telescope ought to show it easily. There’s a nice photo of the pair here.

Instructions for M44: I saved the best for last. M44, also known as the Beehive Cluster or Praesepe (“the manger”), is probably the second best cluster in the sky after the Pleiades. But it’s not as easy to find. The Pleiades have enough bright stars to shine out even in suburban skies, but the Beehive is an aptly named swarm of smaller lights. To complicate matters, M44 is located in Cancer, which has no bright stars.

I usually get to the Beehive from Gemini. Here are some methods that might work for you. My usual path is to draw a line from the extended arm of the western twin, through Pollux, and on in the same direction for about the same distance. Right now that line also intersects Mars, so you could cut your travel time by just drawing a line from Pollux, through Mars, to Praesepe. But that method is only going to work for a few days, maybe a couple of weeks at most, because Mars is on the move (compare its position in the map above with this shot from just a few weeks ago). Finally, if your skies are really nasty, you might try drawing a triangle from Procyon, to Pollux, to Praesepe. It won’t be a perfect equilateral, but it’s close; M44 is just above the point of what would be a perfect equilateral.

Or you could do what I often resort to when I’m in  a rush: find the region between the Gemini twins and Regulus, in Leo (just off-screen to the lower left in the image above), and just sweep around with binoculars or your finder. It’s pretty low-fi, but it’s never failed me yet.

M44 is a true showpiece of the sky, with dozens of stars of even brightness seemingly arranged in a net or grid. It can be seen with the naked eye under dark skies, but it really shines in binoculars. As with the Pleiades, it usually looks better in binos than in telescopes, although a short focal length, rich-field scope might have a wide enough field to show the cluster with some surrounding sky for context.

Coda: The nine open clusters in this  mission are just the tip of the iceberg. This section of the winter sky is littered with hundreds more. There are plenty of bright NGC clusters that rival or exceed many Messiers. The region around the ‘feet’ of the Gemini twins is an especially rich area to sweep with binoculars or a telescope at low power, whether you’re hunting for specific targets or just soaking up the view.

Spring is coming. Although the constellations of winter are high overhead at sunset, they are already starting their long slide toward the western horizon. So get ’em while you can.

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Mission 15: Ring of Fire

January 16, 2010

Mission Objectives: Bright Stars, Constellations

Equipment: Naked eye

Required Time: 2 minutes

Related Missions: Three Astronomical Treats for Naked Eyes, Binoculars, and Telescopes

Introduction: It’s a new mission for a new year. New stars are in the skies, and it’s the perfect time to start exploring the heavens–for the first time if you’re new to this, or exploring it again if you’re an old hand. This mission requires no prior knowledge, experience, or equipment; it’s just about getting out and getting acquainted with the night sky.

Instructions: Go outside after dark, face southeast, and find three stars in a straight, vertical line. These are the stars of Orion’s belt. They are flanked on either side by twin bright stars of roughly equal brightness but different color. On the left is Betelgeuse, an enormous red giant that appears yellow to the naked eye. On the right is Rigel, a blue-white supergiant.

Follow the line made by the belt stars down to even brighter Sirius. Sirius is the brightest star in Earthly skies, but it’s a not a giant or supergiant like Betelgeuse and Rigel. In fact, Sirius is a main-sequence star, a little less than twice the diameter of the sun, but about 26 times as bright. By comparison, Rigel is about 40,000 times as bright as the sun. But Rigel is 773 light years away, whereas Sirius is only 8.6 light years from us–the fifth closest stellar system to our own. Sirius, the Dog Star, is the chief star in the constellation Canis Major.

From Sirius, hang a right-angle left turn and head on to Procyon, “before the dog”, so named because it rises just a few minutes before Sirius from mid-northern latitudes. The small and otherwise dim constellation Canis Minor has little else to recommend it, and Procyon serves mainly as a celestial landmark.

Farther left still, and farther up in the sky, are the twins, Castor and Pollux, at the head of the constellation Gemini. If you have trouble keeping them straight, remember that “Castor is close to Capella, but Pollux is in proximity to Procyon”.

Speaking of Capella, it’s the very bright star directly toward the zenith from Castor and Pollux. It’s a brilliant gem in a ring of prominent stars that mark out the constellation Auriga, the Charioteer (this is not the big ring marked in red on the diagram above, but the much smaller blue-white ring on the upper left).

To the right of Capella is Aldebaran, the burning red eye of Taurus, the Bull. Aldebaran means “the follower”, because this star rises after the Pleiades, which it appears to chase from horizon to horizon (to trace that line, see the previous mission). Aldebaran is an orange giant, meaning that it has exhausted the hydrogen in its core and moved off the main sequence. Without the outward pressure of radiation from hydrogen fusion to prop it up, the core of the star is compacting under gravity and heating up. When it gets hot and dense enough to start fusing helium, Aldebaran will bloat into an immense red giant, like its neighbor, Betelgeuse.

And speaking of Betelgeuse, it lies in the middle of the great circle described by Rigel, Sirius, Procyon, Castor and Pollux, Capella, and Aldebaran. I call it the Ring of Fire–nowhere else in the northern sky is there an equal concentration of bright stars.

Below and to the left (east and north) of the Ring of Fire is Mars, which will be at opposition–opposite the sun, and at its closest approach to Earth–in a couple of weeks. The orbit of Mars is more elliptical than that of Earth, and this will not be one of the better oppositions, but it’s still the best look at the red planet that we’ll get for another two years.

What’s next? This mission was just a lightning run through the bright stars of winter. Their respective constellations are packed full of beautiful targets for binoculars and telescopes, and we’ll look at some of those in future missions. If you’re impatient to get started, download this month’s The Evening Sky Map, haul out your optics, and happy hunting!

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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 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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Here’s something weird

October 21, 2009

Apparently Sirius, hands down the brightest star in the sky, was blood red in antiquity but blazes blue-white today, just 1500 years later. The evidence is compelling. The problem is, no known astrophysical process can account for the change. Read all about it here, and go here for more discussion.

By the way, I love it when stuff like this comes along. It doesn’t mean that science is wrong or that science doesn’t work. It means that there is plenty of stuff that we haven’t figured out, and some of it is, like, huge. As someone who loves figuring stuff out, I take a lot of comfort from that. I want some of that pie for myself. But in this area, at least, I can also get some satisfaction just from looking at other people’s plates.

How wonderful that we have met with a paradox.  Now we have some hope of making progress.  ~Niels Bohr