Algol, also known as Beta Persei, is an eclipsing binary star in the constellation Perseus. The name derives from an Arabic word meaning "ghoul" and into English as Demon Star!
Every 2.87 days Algol drops in brightness from magnitude +2.1 to +3.4. This variability was discovered in 1782 by the English astronomer John Goodricke. The large, bright primary star is partially eclipsed by a smaller, fainter companion and the eclipses last around 10 hours. Eclipse times are widely available online.
I've wanted to capture a pair of images Algol eclipsed and uneclipsed for a long time. I happened to wander outside a couple of days ago and noticed that Algol was at, or near, minimum brightness. There's a star next to Algol in the sky (rho Per) which makes comparison easy: Algol is usually much the brighter of the two, but during eclipse they shine at roughly equal brightness.
I took a 30 second exposure (ISO3200, 18mm) on the camera at around 10.30pm on September 29th; this was a couple of hours after the middle of the eclipse. The following night I was able to take another picture with the same camera settings. Here are the two images.
The pictures were taken late evening but the camera position was slightly different and the position in the sky was slightly different. I cropped out similar sized areas around Algol and used the software Iris to align the images:
Zooming in on Algol (the bright star on the left in each picture) you can see how it varies in brightness compared to the bright star on the right (rho Persei, which is itself and variable star but over much longer periods than Algol). The stars are slightly sausage shaped because they trailed during the 30s exposure. The images haven't been enhanced or retouched in any way!
Finally....a GIF to compare the variation in brightness:
Possibly in the future I'll do some guided exposures with the CCD and attempt some photometry on images captured during the 10 hour eclipses.
Fomalhaut is a tough star to see from these northerly latitudes. You can find it using the popular "Square of Pegasus" stars shown above. Follow a line from the two right-hand stars down to the horizon. It's typically only visible for just a few hours each night and it climbs just 6 degrees above the southern horizon at most. The further north you are, the harder it gets! Way up past 61 degrees north it doesn't rise at all.
In Northumberland on late on autumn evenings there's a bright, lonely star near the southern horizon. It often goes unnoticed - perhaps hidden by nearby (or even distant) buildings or trees. The name of the star is Fomalhaut (pronounced "fum-al-hort").
Before you get the wrong idea Uranography is the art of making making high quality star charts. Celestial cartography is another way to describe it. I've just finished a substantial first attempt to make maps of the entire night sky - including all the stars visible to the unaided eye and lots of star clusters, nebulae and galaxies.
Click here to go to the page with my star charts and more details.
Here's one of the charts.
Setting up the star charts was a great way to become familiar with parts of the sky not visible from Northumberland. These charts are based on the code from open source PP3 Star Charts. I learned a lot of stuff along the way - namely modifying the C++ code to do things slightly differently and compiling it to work on Windows 7. I also modified the original constellation definitions (there are errors in the original). It's not perfect but I'm happy there are no big errors.
At NASTRO outreach sessions I usually begin constellation tours with some advice about how to get started in learning the night sky. Given that there's an app for just about anything you might think the days when you had to learn star patterns to enjoy astronomy is long gone. But It is possible to navigate the night sky by starting with simple star patterns. Over time you can build up your own internal map of the sky without your iPhone or Android ruining your night vision. During the late Summer and Autumn months a natural starting point is the Summer Triangle.
Also the the story behind the Summer Triangle is sort of interesting! The Summer Triangle (blue-dashed triangle on the star chart below) is formed between three of the brightest stars in the sky: Vega, Deneb and Altair.
In the 1920s the Internationational Astronomical Union decided to formalise the various star patterns that astronomers used to specify star locations. With the advent of astrophotography and the flood of variable star discoveries (which were named according to the constellation) it became important to know where one constellation ended and another began. They drew up a list of 88 constellations which are still use today, today. On the star chart above the constellations are patterns connected by the green lines (e.g. Aquila, Sagitta and so on).
There are other interesting star patterns in the sky - The Plough and Summer Triangle being the most famous - which are not part of the official list. We call these patterns asterisms. The Plough stars are part of the constellation Ursa Major. The Summer Triangle stars are part of three different constellations: Cygnus, Lyra and Aquila.
The Summer Triangle was popularised by Sir Patrick Moore on The Sky at Night and in his numerous astronomy books from the 1950s onwards. References to the Summer Triangle (or Great Triangle) can be traced back to the start of the 20th century.
Back to the Summer Triangle. Vega and Deneb mark the northernmost corners of the triangle. Altair is the star at the southern corner. The Milky Way runs through the Triangle and appears to split into two streams (separated by the Cygnus rift).
Vega is brightest star and Altair is slightly dimmer. Deneb appears to be the faintest of the three but that's just an illusion! Vega and Altair are quite nearby - 17 and 25 light-years away respectively. Deneb is an absolutely brilliant beacon shining across 1,800 light-years of space. If Deneb were at the distance of Altair it would shine as brightly as the crescent moon does! After identifying the Summer Triangle it becomes easier to find the surrounding constellations. For example, with Vega comes the tiny constellation of Lyra. Within the borders of Lyra is the Ring Nebula. Deneb is the leading star of Cygnus. When the shape of Cygnus can be recognised there are many star clusters to be found and one of the most beautiful double stars in the night sky. There are other smaller constellations with distinctive shapes nearby (Delphinus - a dolphin. And Sagitta - an arrow) in which a great number of incredible deepsky objects are waiting to be seen through your binoculars and telescopes.
The Summer Triangle will be around for awhile longer; despite the name it is visible for much of the autumn and into winter. But the relatively pleasant evenings of late summer are definitely the best to go out and find it for the first time.
The beginning of a long term project: a constellation guide illustrated with my own star charts and astro images. First up is Vulpecula, the Fox. (Keeping it simple to begin with!) One down. Eighty seven to go.
Off to the airport soon. Newcastle to Kuala Lumpur via Dubai. Then a bit of wait before my next flight to Miri. I'll be dashing to different places and ending up in Singapore by the end of the week. Almost on the equator and a nice place to see the entire sky.
I've no idea whether I'll see the night sky while I'm there. Probably too much light pollution in places I'm staying. Astronomically, my primary goal is to see the Southern Cross (aka Crux). And Alpha Centauri - very nearby in the sky. I missed out seeing them from Venezuela last year because they were too close to the Sun. No binoculars or camera going with me so it's purely naked-eye astronomy.
The short nights of late spring don't give much time to do astronomy. Despite this there are some interesting constellations to be explored! One of my favourites is Corona Borealis - the Northern Crown. At this time of the year it is high in the southern sky when it gets dark. If you've not seen this little constellation before, well, it's easy to find by star hopping from The Plough to the brilliant orange star Arcturus and then onto Corona Borealis. Like this:
It an easily recognisable constellation - just a small semi-circle of stars. And one of the few that actually resembles the object it is meant to represent:
Twelve million years ago, give or take, a star exploded in nearby galaxy M82. Light from this event is arriving at Earth right now. Astronomers given this supernova the official designation SN 2014J.
Here's a picture I took with the 8 inch telescope last night. The supernova is indicated by the red lines.
This supernova has been classified as type 1a - a white-dwarf detonation. The precise mechanism is not well understood. It might be that the white dwarf star - probably about the size of the Earth but and with a mass comparable to the Sun - was drawing material from a companion star onto it and a runaway nuclear chain reaction led to the complete destruction. Or maybe two white dwarfs collided. Whatever the case the tiny, tiny star was obliterated in one of the biggest bangs in the universe.
M82 is a reasonably bright galaxy and I took an image of it last Autumn. Now I have before and after images of a supernova:
M82 is fairly bright galaxy in the night sky and quite easy to find even without a GoTo telescope. M82 is not far from the familiar seven star pattern of The Plough - and always visible from the UK. The galaxy is best viewed later in the evening when it is almost overhead in the UK.
SN 2014J will continue to increase in brightness in the coming days. The luminosity increase is not instantaneous. Radioactive Nickel-56 is produced during the supernova and when it decays it excites the surrounding gas to incandescence. The half-life of 6 days means that peak brightness occurs well after the supernova first happens.
The western sky is looking particularly busy and South America is a great place to watch it! I've framed an area of sky towards the west about half an hour after sunset using Skymap Pro:
The rectangle is the frame of my Nikon D80 at 18mm. This frame should encompass three planets and some bright stars, including Spica, Antares and Alpha Centauri (aka Rigil Kentaurus). I've picked my spot to take the picture - about quarter of mile from where I'm staying in San Antonio. The only problem might be some nearby hills which could potentially hide alpha Centauri.
At the moment the weather isn't looking great but the above scene won't change too much over the coming days: Venus will glide past Saturn and Mercury will get a little easier to see.
It was a bit unsettling to not immediately recognise the stars as they appeared after sunset. I wasn't sure if the first stars to appear were Vega, Altair or something else. Looking towards the crescent moon, which I knew was in Scorpius, I knew the red-orange star Antares must be near. Very soon the other stars appeared and for the first time I could see the entire constellation for the first time.
Antares (meaning rival of Mars) is the bright orange star in the picture. It is flanked by two fainter stars, rather like Altair, the southern star of the Summer Triangle is. In the above picture the Northumberland horizon runs roughly from upper left to lower right cleanly bisecting the Scorpion just beneath Antares. I've never had a good view of this part of the sky!
Scorpius is definitely my new favourite constellation! As darkness fell and I could see several clusters of the stars, looking like knots in the Milky Way. There was a particularly bright one near the star Shaula (the "stinger" of the Scorpion).
That's Messier 7 (Ptolemy's cluster). It's the southernmost object of Messier's list. I wish I had my telescope here! M7 has a distinct cross shape through the binoculars (it shows up well in the picture). We really miss out in terms of the Milky Way from the UK.
Dr Adrian Jannetta
Guitar strummin' explorer of the universe. Mild mannered maths teacher by day and astronomer by night.