Vela – The Amazing Sky

April 27, 2014April 27, 2014

The Night Sky’s Two Brightest Stars

The two brightest stars in the night sky shine in the southern sky.

Here are Sirius (at right) and Canopus (at bottom left), the brightest and second brightest stars in the night sky, together near the southern Milky Way.

My image also captures the huge loops of the Gum Nebula, thought to be the remains of a supernova that blew up a million years ago. It’s utterly invisible to the naked eye, but Sirius and Canopus stand out as brilliant stars even from light polluted sites.

Sirius can be seen from northern latitudes but Canopus is below the horizon for any location north of 37° North or so. I shot this image from Australia where these stars pass overhead.

Sirius is a hot blue-white star 8.6 light years away. Canopus appears slightly dimmer but only because it lies much farther away, at some 310 light years. In reality it is a supergiant yellow-white star that shines with a luminosity 15,000 times that of our Sun.

This image takes in Canopus at bottom right, next to the Large Magellanic Cloud, and with the southern Milky Way sweeping across the top, with the Carina Nebula and its attendant star clusters at top left and parts of the Gum Nebula at right.

Here are a few cocktail party facts about Canopus:

• In 480,000 years its motion around the Galaxy will bring Canopus close enough to Earth that it will become the brightest star in our night sky, outranking Sirius.

• The origin of its name is a mystery. One idea is that the star is named for the pilot of the ship that took Menelaus to Troy on the quest to re-capture Helen.

• Canopus, the star, was used in ancient times as a key navigation star for those sailing to southern seas, as it would have risen above the southern horizon from latitudes below 35° North back around 2000 BCE.

• Today, Canopus is charted as the brightest star in the constellation of Carina the Keel, part of the ancient constellation of Argo Navis, named for the ship sailed by Jason and the Argonauts.

April 23, 2014

Stellar Graveyard in Vela

This is what’s left of a star that exploded in ancient times.

This is the Vela Supernova Remnant, an object in the southern sky in the constellation of Vela the Sail. The wispy tendrils of magenta and cyan are all that’s left of the outer layers of giant star that exploded about 12,000 years ago.

Cluttering the field at left are amorphous patches of star-forming nebulosity that are part of the much larger Gum Nebula complex.

The supernova was only about 800 light years away so it would have been a brilliant sight in the sky to neolithic observers, far outshining any other stars. But no record exists of anyone seeing it.

The star didn’t destroy itself completely – its core collapsed to form a pulsar, an ultra-dense ball of neutrons, in this case spinning about 11 times a second. The pulsar is in this field but it’s much too faint to show up in visible light.

I shot this earlier this month from Australia where Vela sails directly overhead. The field is about 6° by 4°, the amount of sky framed by high power binoculars. The brighter parts of the Vela Remnant can be picked out in large amateur telescopes – I’ve seen bits of it in my 10-inch telescope – but this is certainly a challenging object to see, even with aided eyes.

December 17, 2012December 17, 2012

Remains of a Star: The Vela Supernova Remnant

Amid a maze of glowing nebulas sits a tracery of magenta and cyan that was once a star.

This image takes in the Vela Supernova Remnant. You can see it as the lacework of gas in the centre of the field. Oddly enough, it sits in the middle of the vast Gum Nebula, the subject of my previous post, an object also thought to be a supernova remnant but one much older and closer. The Vela Supernova Remnant here likely comes from a supergiant star that exploded about 10,000 years ago. It, too, would have been quite a sight to the earliest of civilizations.

The field in the southern constellation of Vela also contains many other classic red and pink nebulas, but ones that are forming new stars, not the remains of dead ones. Most carry designations from astronomer Colin Gum’s catalog from the 1950s and have no numbers from the more familiar NGC or IC catalogs amateur stargazers refer to in their scanning of the skies. Yet, these Gum nebulas show up easily in photos.

I used a 135mm telephoto lens to take this image and it encompasses a field similar to what binoculars would frame. Except, it takes long exposure photos to show these nebulas. I looked last night at the Vela SNR with my 25cm reflector telescope and could just barely see the main arc of nebulosity as a grey ghost in the eyepiece. And that was under perfect dark Australian sky conditions.

December 17, 2012December 17, 2012

Giant Bubble in the Southern Sky

The southern sky contains what must be the largest nebula in our sky, a giant bubble spanning a wide swath of the Milky Way.

This is the object known as the Gum Nebula. You can see it in my previous post, in the ultrawide view of the southern sky. Here I’m framing it with a normal 50mm lens that covers about 50° of sky. The Gum Nebula is completely invisible to the eye and shows up only on photos. It wasn’t even discovered until the 1950s, by Australian astronomer Colin Gum. It is #12 in his catalog of southern sky nebulas. I’ve always thought this was an example of an interstellar bubble, blown by intense winds from hot blue stars, of which there are many in this part of the Milky Way in Vela and Puppis. At left are the four stars of the False Cross in Carina and Vela.

But some sources claim this is a supernova remnant, the blasted remains of a star that blew up 1 to 2 million years ago. It is big because it is close by, just 450 to 1500 light years away depending on what side if the remnant you measure. If that’s the case, the star that exploded would have been quite a shadow-casting sight in our prehistoric sky, assuming it was that close to us when it blew up and was in the night sky at the time.

Either way, it is a great target for amateur photographers, and now with digital cameras it is easy to record. This night, some haze moving through added the photogenic glows around all the stars to bring out their colours.