Betelgeuse: A Supergiant To Love

In the evening hours of late winter and early spring in the northern mid-latitudes like Ontario, the constellation Orion is a very familiar friend. The brightest star in Orion, Betelgeuse, is itself endlessly fascinating.

If you can picture the constellation then you can find Betelgeuse right away. It’s the orange-shaded bright star at the “right shoulder” of Orion – or on the left as we see the asterism. The other stars in Orion don’t have a noticeable colour most of the time, but Betelgeuse is decidedly reddish-orange.

Constellation Orion rising over a suburban street in Burlington, Ontario, at about 9:45 PM on the evening of 2013 March 26. Betelgeuse, the brightest star in Orion, is in the middle of the frame and about 1/8th of the way down from the top.

Betelgeuse has been known as an interesting star since antiquity, but what astronomers have learned in the past 20 or more years make it all the more fascinating. For one thing, we don’t know how far away it is too much in the way of accuracy. Betelgeuse is relatively close to earth – somewhere between 400 and 700 light years away, or only about half as far as the Great Nebula in Orion, which we see with our naked eyes as the third “star” in the sword hanging from Orion’s belt. The lack of accuracy is no indication of lack of trying. For stars of this distance, astronomers often use a triangulation method called parallax to work out distances. Betelgeuse is hard to pin down this way because it is not in fact a “point” of light in the sky. The star is so big and so close that it actually has been photographed as a disk by the Hubble Space Telescope in 1995 (Gilliland & Dupree. 1996). It has a complex outer envelope that is changing its size and shape, and makes the parallax method no better than about 1 part in 5 for accuracy. The star is about 640 light years away, but that’s plus & minus 140 light years!

The size of this star is also staggering. Its diameter is approximately the same as the diameter of the orbit of Saturn in our own solar system. It’s also shining about 100,000 times as bright as our own sun. It’s likely a relatively young star compared to our own sun, and some time in the near future (in astronomical terms) it will likely explode as a supernova.

Recent scientific papers on Betelgeuse have gathered together more observations of the star itself and have tried to interpret various areas that look brighter to us as either bright patches on a darker background, or possibly  as bright areas areas showing up through overlaying dark features.

This star is also moving quickly toward a linear “wall” of material that is part of the local stellar environment. Betelgeuse has a shell of glowing material thought to be part of the material blown off of the surface of the star in the past. This shell will hit the wall in about 5,000 years, followed by the star itself about 12,000 years later (Decin et al. 2012). Don’t wait up for it.

Sources

Decin et al. 2012. The enigmatic nature of the circumstellar envelope and bow shock surrounding Betelgeuse as revealed by Herschel. I. Evidence of clumps, multiple arcs, and a linear bar-like structure. Astronomy and Astrophysics 548, A113 (http://www.aanda.org/index.php?option=com_article&access=standard&Itemid=129&url=/articles/aa/full_html/2012/12/aa19792-12/aa19792-12.html).

Gilliland & Dupree. 1996. HST imaging of Betelgeuse. Stellar surface structure: proceedings of the 176th Symposium of the International Astronomical Union, held in Vienna, Austria, October 9-13, 1995. Edited by Klaus G. Strassmeier and Jeffrey L. Linsky. International Astronomical Union. Symposium no. 176, Kluwer Academic Publishers, Dordrecht, p.165 (http://adsabs.harvard.edu/full/1996IAUS..176..165G)

Copyright © 2013 David Allan Galbraith

 

 

Probing Deep Space from an Urban Apartment Balcony

Living in a large urban centre in a small apartment just one level off of the ground has its challenges for astronomy. First of all, I don’t have a garage or other place I can conveniently store my equipment; many astronomers I know have a space set up in a garage or shed where they can keep their gear at close to outdoor temperature all year. No such luck here. Second, my “at home” viewing area is a concrete balcony that is, I suppose, about 6 square meters at the most. It projects out to the west, which means I do see some nice sunsets, but my particular view is also pretty much obscured by trees, houses, and in my case part of the Niagara Escarpment. I also have the balcony of the apartment above mine right above mine, which means I can’t put a telescope on the balcony and see the zenith – straight up.

It’s also taken my a while to work out the geometry of the building. From the farthest out I can put a telescope on my balcony, Polaris just peeks over the top of the building, in the direction of a flood light that shines down on our parking area, which means that it’s virtually impossible to get a good polar alignment optically.

Not exactly a dark sky area.

Still, the urge to observe and photograph is strong, and a few things are amenable to urban star watchers even under less than ideal circumstances. The first thing is the moon. While nothing will move clouds out of the way, even in the most light-polluted areas the moon is still a great view. on a clear night Jupiter, Mars, Saturn, and Venus are all observable from cities too. They are so bright in comparison to stars and deep sky objects like galaxies and nebulae that there’s enough contrast to see them pretty well. Even the Galilean moons of Jupiter are pretty reliable from urban vantage.

My particular balcony’s situation means that in late winter evening views bring the Constellation Orion into view. Right now, Jupiter isn’t far off of Orion, and once a month the moon makes an appearance in the area, too. I was pretty happy, therefore, to see a clear evening on Sunday 17 March 2013 – and all three swung into view.

The Constellation Orion and the moon presented a lovely view from my apartment in Hamilton on 17 March 2013.

The sky around Orion is particularly rich in interesting objects, and it’s one of my favourite parts of the sky. As soon as I could get a clear view of the area from Orion to the Pleiades, just to the east of Orion and past the moon, I set up a camera and took some overall photos with a wide-angle lens. The brightest individual objects in the sky were the moon and Jupiter, very near by. These two bright objects were great to capture with a telephoto lens.

The moon and Jupiter passed within three degrees of each other on the evening of 17 March 2013. The view with a 500 mm telephoto lens and camera on a tripod.

After a few photos of the overall scene I concentrated on the moon for a bit. Actually, this is a bit of a literary slight-of-hand, because I’d been preparing to use a telescope for a little while on the 17th, and had set up my big EQ6Pro telescope mount ahead of time. I settled on an approximate alignment to Polaris as “close enough for apartment work” and then mounted my old 80 mm f/15 refracting telescope on the mount. With a focal length of 1,500 mm this long white telescope gives nice views of the moon. I took a few shots at 1/100 of a second, ISO 400.

The moon, photographed on 17 March 2013 from an apartment balcony in Hamilton, Ontario, with an 80 mm f/15 refracting telescope and Nikon D800 camera.

The view of the moon was nice on the 17th. The terminator was passing through the Sea of Tranquility, meaning that the landing site of the 1969 Apollo 11 mission was likely just experiencing sunrise. Crater Theophilus, one of my favourites, was nicely illuminated. The image above is the whole image, reduced in resolution. Below is a section centred near Theophilus cropped but not reduced in resolution. The Apollo 11 landing site was approximately in the middle of this view left to right, and just below the top edge of the frame.

A portion of the photo of the moon above, taken on 17 March 2013, unreduced in resolution. Crater Theophilus is near the middle of this view, with a four-peaked mountain in its centre, just caught by the morning rays of the sun.

Once I had my fill of the moon I decided to go after a deep sky prize for the first time: the Great Nebula in Orion, or M42. This is an amazing region of space, about 1000 light-years away, where new stars are being born in huge clouds of gas and dust. We can see this nebula (Latin for cloud) with our own eyes on a clear night. It’s the middle “star” in the “sword” hanging down from Orion’s belt. It’s even visible on the wide-angle photo at the beginning of this post, looking like a star.

The EQ6Pro mount I was using is equipped with a digital inventor of many objects in the sky. I simply entered “M42” in the keypad and the mount took over, pointing the telescope right at the nebula! I took a few photos right away. My biggest challenge was focusing the telescope. I was not able to see any stars at all through the camera viewfinder. I took a series of exposures, adjusting focus between each one. I was really happy to see something of the nebula, though. The photo below was among the better of the group, taken with the Nikon D800 at ISO 6400, 15 second exposure.

My first photo of th Great Nebula in Orion – M42. The good news? Lots of room for improvement.

One of the cardinal rules in using a telescope, especially for photography, is that it’s best if the telescope itself is at the same temperature as the air. When I started my March 17 observing I set out a larger telescope, a Sky-Watcher 200 mm f/5 Newtonian reflector (focal length 1000 mm, designed for imaging), on the balcony to cool down. By the time I was ready to try something more challenging than the moon, it was ready. I set this larger scope onto the mount and re-aligned it. What a difference! The larger diameter of this telescope – 200 mm compared to 80 mm for the refractor – gathers a lot more light. With the camera on live-view I was immediately able to see the four central stars in the nebula, known as the Trapezium, and focus the telescope on them. After experimenting with exposures I settled on ISO 640 and 30 seconds, and was quietly pleased with the results. This is just a first stab at a “deep sky object” for me, but it looks promising, especially for those times to come when I will be able to align the mount a little better (eliminating the slight streaking of the stars into trails visible here), and get out of areas of intense light pollution (which improves contrast and detail in astrophotography).

The Great Nebula in Orion photographed with a 200mm Newtonian Telescope, 17 March 2013, from an apartment balcony in Hamilton, Ontario.

The relative sizes of the images I’ve presented here are a little misleading. The nebula is about a degree across in the sky, compared to half a degree for the moon. Much less detail came through on M42 because the moon is so much brighter that it shone through the sky glow of urban light pollution, and because among other things it required a much shorter exposure. Also, the 80 mm refractor has a focal length of 1500 mm, while the much beefier-looking Newtonian is just 1000 mm. Like camera lenses, this means that the refractor actually magnifies things more than the Newtonian does, and I used the refractor for the images of the moon. It’s also worth noting that having the moon so close to Orion on the 17th made photography of the nebula even harder. Its bright light spills all over the sky, and even into the telescope, reducing usable contrast on the nebula.

Copyright © David Allan Galbraith 2013

The Equinox is coming. So is the Equilux. So what’s the difference? About four days.

A term from astronomy that has entered common use is Equinox, which translated from its Latin roots roughly means “Equal Night.” Most people think that the Spring (or Vernal) Equinox and the Fall (or Autumnal) Equinox are the days when the length of the daylight and the length of the night are equal. Close, but not quite right.

As the days lengthen from winter toward summer, there certainly is a day during which the length of time we see sunlight and the length of time it’s dark are roughly the same. Technically, however, the timing of each Equinox is defined as the moment when the earth passes a particular point in its orbit around the sun. It’s not defined by the local length of the day.

We have extended our imaginations into space, and covered it with geometric patterns. One of those patterns is an imaginary circle that runs around the entire sky and is called the ecliptic. This is the circle that marks the apparent position of the sun throughout each year, relative to the background stars. It’s called “ecliptic” because of its importance in determining the dates of eclipses. For a lunar or a solar eclipse to take place, the sun, moon, and earth all have to be in alignment with the ecliptic.

Because much of the solar system is in a pretty flat configuration, most of what happens in the solar system also happens near the ecliptic. The orbits of the earth, Mars, Venus, Jupiter, and many other things in the solar system lie in more or less the same plane. So, when you are able to spot any of the planets you’re seeing, approximately, where the ecliptic lies in the sky.

Another similar geometric pattern or circle that is projected into the sky for practical reasons is defined by the earth’s own equator. Astronomers can plot a line across the sky which corresponds, in the “up” direction, to where the equator is on earth. If that’s a little hard to envision, just consider the North Star, Polaris. By accident it sits within a degree of the place in the sky directly above the earth’s north pole (the rotational pole, not the magnetic pole. They’re different things, for another day). From Polaris the celestial equator is 90 degrees south in all directions.

Right. So, two circles projected up in the sky (Picture an orange with two rubber bands around its middle that cross each other as viewed from the inside). They are tilted with respect to each other by the same amount as the earth’s rotation is tilted relative to the position of the sun – around 23 degrees. Each Equinox is defined as the time at which the earth passes the place where the two lines cross. At that moment, the terminator – the place where the sunlit side of the earth and the night side of the earth meet – is at right angles to the earth’s equator.

Now, you’d think that this perpendicular arrangement would mean day and night are of equal length, and geometrically it’s true. However, what we actually see is much more complicated. The apparent length of daylight and night differs from place to place on earth. One of the big factors is the bending effect of the earth’s atmosphere. We sit under an ocean of air, and one of the consequences of our atmosphere is that light is bent as it comes in from space; air acts like a huge lens. The closer an object is to the horizon (like the sun at sunset or sunrise) the more the bending is apparent. This is because the light at these low angles must pass through much more air to reach us. It acts as a thicker lens closer to the horizon.

The consequence of this bending of sunlight is that the time something actually happens in the sky is not necessarily the time we see it happening from our vantage point under the atmosphere. In fact, this bending is enough that at the horizon it’s enough to make the sun appear to be more than its own diameter “earlier” in rising than it would without the atmosphere there. A staggering thought – when we see the sun just getting up over the horizon in the morning, it’s actually still below the horizon geometrically!

The other factor is the apparent size of the sun. From the earth’s perspective the sun is about a half a degree across, compared to the whole 360 degrees of the sky. Sunrise and sunset do not happen instantaneously. Sunrise is defined as the moment that the sun’s disk just appears on the horizon for any particular morning. Sunset is defined as the moment when the last bit of the sun just disappears past the horizon from any particular location.

These two things combined are enough of an effect that the Equilux, the day that has equal hours and minutes of sun above and below the horizon, is about four days before the Vernal Equinox and about four days after the Autumnal Equinox in the area of Hamilton, Ontario. The timing of the Equilux may be different in your location. In 2013 the Spring Equilux – the date that daylight and nighttime hours are closest to being 12 and 12 – falls on 16 March. The corresponding Equinox this year takes place about 7:02 AM on 20 March.

In September 2013 the Autumnal Equinox, marking the official beginning of fall, is at 4:44 PM on the 22nd. The Fall Equilux, however, for Hamilton is on 25 September.

Sources:

• Thanks to the on-line calendar of the Hamilton Amateur Astronomers for the Equilux and Equinox dates and times for 2013. http://amateurastronomy.org/

Copyright © David Allan Galbraith 2013

Someone Finally Saw Comet C/2011 L4 (PanSTARRS)!

A biology contact of mine, Dr. David Hillis, and his students saw Comet C/2011 L4 (PanSTARRS) tonight (12 March 2013) and actually got a great photo! He has generously allowed me to post one of his photos here at Pine River Observatory.

Their vantage point was David’s Double Helix Ranch in Texas. They saw the comet at a moment that had been promoted in many sources of information on astronomy, when it was visible near the new moon. Here’s the photo:

Thanks David! A wonderful photograph.

Here’s a link to his ranch’s web site, to say thanks for letting me post his photo: http://doublehelixranch.com/.  Drop by and say hello!

Hopefully we’ll get some nice weather soon in Ontario and be able to make up for lost comet-viewing time. Sometime.

PS: Please respect David’s rights regarding his photo. If you want to use this photo in any way, please send him a message and ask. His email address is on his web site. I asked and he said yes.

Update 6 AM 13 March: Here’s a link to a lovely photo of the moon and the comet taken in Burbank, California last night by “5650 Imaging”: http://www.5650imaging.com/Landscapes/Moon/24984509_tKt9kN#!i=2406020175&k=5hT763K&lb=1&s=A

A Report on Expedition One to Comet C/2011 L4 (PANSTARRS)

Last night (8 March) one of my photography students and I gave it a very good try, but the clouds didn’t let us actually see Comet C/2011 L4 (PANSTARRS). We met at the parking lot of Canadian Warplane Heritage, beside Hamilton’s international airport,at 6 PM. Despite repeated forecasts for a sunny afternoon – and the Hamilton clear sky chart showing fairly good observing conditions at the time – the cloud deck was 50% complete and 90% to the west: just 2° or less of clear sky in the west.

We decided not to give up, though, and drove like crazy toward the gap in the clouds. We ended up droving west past Brantford and got a little more clear sky, but ultimately, we missed it… there was a little gap in the clouds along the horizon, and we were hopeful. We saw aircraft in there but no comet. Too late, too many clouds. Also, we were depending on a generalized chart of the sky as to where the comet should be. I suspect that by the time we got to our spot and stopped the comet has set.

The western horizon west of Brantford, Ontario, at 7 PM on 8 March 2013: too late to see Comet C/2011 L4 (PANSTARRS). Did see lots of planes, though, like the one in this photo.

The forecast for Saturday 9 March is for good weather; some cloud in the afternoon, but hopefully the little part of the sky we need to see the comet has a chance of being clear. The clear sky chart suggests that by 6 PM (18:00) we might have clear skies: http://cleardarksky.com/c/Hamiltonkey.html.

To reduce the uncertainty in where to look, I loaded the orbital elements for the comet into Stellarium, a sky chart program I use, and plotted the expected locations for Comet C/2011 L4 (PANSTARRS) for three specific times tonight as viewed from Dundas Ontario. Here are the expected bearings for the comet tonight (relative to the horizon and north), and taking into account the bending effects of the atmosphere:

At 6:30 PM: azimuth 255° 26′, altitude 7° 18′

At 6:40 PM: azimuth 257° 13′, altitude 5° 35′

At 6:50 PM: azimuth 258° 58′, altitude 3° 40′

Azimuth is “compass direction.” 255° is 15° south of west. The sun will set at 265° on the 9th, at about 6:18 PM. So, the comet should be a bit further south than the place the sun sets.

Altitude is elevation above the horizon. The width of a thumb held at arm’s length is about 2°; the width of a fist at arm’s length is about 10°. So, the comet should be closer to the horizon than the width of a fist at arm’s length at 6:30. It’ll take only a little in the way of stuff on the horizon to lose it.

The upshot of all of this is that it’s a good idea to get as high as possible before looking for this comet 🙂

Another entry will be filed when the next expedition reports back.

© David Allan Galbraith 2013