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A Bright Nova Appears in Delphinus

August 15, 2013 2 comments

Last night a bright nova was discovered in the constellation of Delphinus. It’s bright by nova standards: you normally need telescopes to see novae but this can can be seen with the naked eye – just! – and is easily spottable through binoculars. At the time of writing it has been observed at magnitude 6.3 by Koichi Itagaki, of Yamagata, Japan, and at magnitude 6.0 by Patrick Schmeer, of Bischmisheim, Germany. This means that under dark skies, free from light pollution, with good seeing conditions and good eyesight, it’s within the limit of human eyesight. If you’re in a city though, or if your eyesight isn’t perfect, you’ll need binoculars.

UPDATE 16/08/13 at 1525UT
The British Astronomical Association e-bulletin 00757 is reporting that observations have been submitted to the AAVSO database suggesting the Nova Delphini 2013 has brightened to magnitude +4.5, making it an easy naked-eye object from rural and many suburban sites.

UPDATE 17/08/13 at 0630UT
The AAVSO light curves suggest that Nova Delphini 2013 is dimming, and is currently at magnitude +4.9. This is still naked eye under dark skies and an easy binocular object from cities but get outside as soon as it’s dark and clear; it’s going to keep dimming and soon won’t be naked eye.

UPDATE 18/08/13 at 1430 UT
Although it has dimmed slightly from its maximum brightness of +4.4 magnitudes, it has stayed at +4.9 magnitudes for almost two days now, meaning it’s still naked eye.

UPDATE 22/08/13 at 1330 UT
Nova Delphinus 2013 has dropped below +5.5 magnitude, and will probably drop below human eye detectability in a few days time (it’s already a non-naked-eye object except in very dark sky sites).

Here are some finder charts for the nova, produced using the excellent (free!) Stellarium package.

Nova Delphini 2013 marked with a +

Nova Delphini 2013 marked with a +

Your first task will be to locate the small constellation of Delphinus. Luckily, that’s really easy at the moment. It’s high in the south around midnight (SE in the evening), and right next to the prominent stars of the Summer Triangle. The brightest stars in Delphinus make up a tiny diamond shape in the sky. Got it? OK, here’s where it gets a little trickier.

Three steps to Nova Delphini 2013

Three steps to Nova Delphini 2013 marked with a +

Step 1: Find the diamond shape of Delphinus, shown in the lower left portion of this star chart, with the bright stars of the diamond α, β, γ, and δ labelled (along with ζ nearby).

Step 2: Draw a line from the lower left star of the diamond, δ, past the upper right star, α, but missing it slightly to the “left” of α. Continue for approx. five times the α-δ distance. Here you’ll find another four stars in a diamond of almost exactly the same shape and orientation as (albeit slightly smaller than) the bright diamond of Delphinus. These stars are all really faint. Their magnitudes are marked on the chart above, and they’re all at the very limit of naked eye visibility. Use binoculars if you can’t see them directly.

Step 3: Continue your line onwards, through the lower left star of this fainter diamond to the upper right star, and now take an approximately 45° turn to the “right”, past a very faint star (magnitude 7.85) to the new nova!

(The bright star in the top left of this star chart is 29 Vul, magnitude 4.8)

Nova means “new”, a term coined in 1572 by astronomer Tycho Brahe after he discovered a “new star” in the constellation of Cassiopeia. But these stars aren’t new at all. In fact their brightness is a result of a giant explosion on the surface of a dead white dwarf star.

White dwarf stars form when small stars die and collapse down into a much smaller volume. If there’s another star nearby then the gravity of the white dwarf star can draw some hydrogen gas from the surface of its neighbour onto its own surface. This gas builds up until there is a sufficient quantity of it that it undergoes runaway nuclear fusion, igniting, flaring off, and temporarily brightening the otherwise very faint white dwarf.

No one’s quite sure how this new nova will develop. It might brighten further, or it might begin to dim over the course of days or weeks. All the more reason to get out an find it as soon as you have clear skies. Happy nova hunting!

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Constellation of the Month: Lyra

August 1, 2013 Leave a comment

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August’s evening skies are dominated by the Summer Triangle high in the south, made up of the three brightest stars in three different constellations, the stars Deneb in Cygnus, Altair in Aquila, and brilliant Vega in Lyra.

Vega is a magnitude 0 star, the fifth brightest star in the night sky, and the third brightest (after Sirius and Arcturus) visible to UK stargazers.

Look high in the south (almost directly overhead) in the late evenings in August and the very bright white star you’ll see is Vega. Look “down and left” of Vega and you’ll see the four other bright stars of Lyra in a rhombus shape.

Lyra represents the lyre of Orpheus, and it’s a great little constellation to observe through a telescope since, despite its diminutive size, is home to two Messier objects, M56 and M57.

Messier 56 (marked 2 above) is a loose globular cluster lying about 33000 light years away. It sits halfway along a line drawn between the “lowest” star of the lyre (the one furthest from Vega) and Albireo (beta Cygni). Through binoculars or a small telescope it looks just like a fuzzy star. You’ll need a pretty decent sized telescope (20cm+) to resolve individual stars.

Messier 57 (marked 1 above) is known as the Ring Nebula, and is one of the most-photographed of astronomical objects. It’s a planetary nebula, an expanding shell of gas that’s been puffed off by a giant red star in its death throes. Small scopes should show the elliptical shape but you’ll need a larger (20cm+) scope to see the hole in the middle and any features within the nebula. M57 is easy to find as it sits almost exactly half way between the two “lowest” stars of Lyra (the two furthest from Vega) beta and gamma Lyrae.

Constellation of the Month: Hercules

The month of June has the shortest nights of the year (for northern hemisphere stargazers), but there’s still plenty to see if you wait till the sky gets dark after midnight.

Sitting high in the south – almost directly overhead – during June is the constellation of Hercules.

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The body of Hercules is made up of four stars in an asterism known as The Keystone. The four stars in The Keystone, like all the star in Hercules, are not especially bright, so the pattern doesn’t stand out all that clearly. To find it draw a line from the bright orange star Arcturus to the bright white star Vega. Hercules sits about 2/3 of the way along this line.

Once you find the Keystone try and trace the four lines that come off each corner, Hercules’s arms and legs.

But the most interesting feature in Hercules is the faint fuzzy patch known as the Great Globular Cluster in Hercules, M13 (marked with a + above).

M13 lies on a line drawn between two of the stars of the Keystone, ζ and η Her. It’s just visible to the naked eye in dark sky conditions (which you won’t get during the summer months) but is easily found using binoculars. It will look like a fuzzy out-of-focus star.

In fact it is a globular (globe-shape) cluster of around 300,000 very old stars, orbiting our galaxy.

If you’ve got a powerful telescope then you should be able to make out individual stars within this cluster.

Constellation of the Month: Leo the Lion

Head outside during April just as the sky gets properly dark and sitting high in the south is the constellation of Leo the Lion.

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Leo is well-known as it’s one of the signs of the zodiac, and therefore one of the constellations through which the planets, Sun and Moon pass over the course of the year.

Leo is also well-known due to its most prominent feature, a pattern of stars within the constellation (called an asterism) known as The Sickle, which looks like a backwards question mark, with the bright star Regulus as the dot.

Regulus is known as the king star, and is one of the brightest stars in the sky, shining blue-white in late winter and spring.

Within the constellation of Leo are two groups of galaxies, marked as 1 and 2 on the chart above.

1. The Leo Triplet: M65, M66, and NGC3628
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2. The M96 Group: Including M95 & M96
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Any of these galaxies can be seen with even a small telescope, but their detailed structure can only really be seen in larger scopes.

Enjoy the spring skies, and happy galaxy hunting!

Maps and descriptions like this one for each of the 88 constellations can be found in my new book, Stargazing for Dummies. Click on the image on the right for more info.

Bye-bye Orion…

Tonight is a symbolic and poignant one for me here in Glasgow; tonight Orion’s right foot Rigel sets at 2232, by which point astronomical twilight won’t even have ended.

Screen capture from the excellent Starwalk app for iPhone

This means that Orion is setting into the glow of the Sun in the west, and very soon won’t be visible at all. By the end of April Orion will be setting by 2100, only minutes after the Sun, so will be invisible until it appears next winter.

These dates will differ somewhat for you depending on where you are: if you’re further north than Glasgow Orion will already have begun to vanish in the longer days, and if you’re further south it will linger a bit, but to all intents and purposes that’s it for Orion till winter.

So take the opportunity to go and see Orion the Hunter while you can, before he vanishes into the glare of the Sun.

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