Fire and Ice

In my last post, I invited you to face west and gaze upon a gem of an asterism called the Diamond of Virgo. This time, let’s look for the fire in the ice.

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First, look about midway between the stars Denebola (denn-EBB-oh-luh) in Leo the Lion and Cor Caroli (core CARE-oh-lye) in Canes Venatici the Hunting Dogs. From a dark site, you should be able to spot a naked-eye sparkly cloud. This is the Coma Star Cluster, an open cluster in the constellation Coma Berenices (KOH-mah bare-uh-NIGH-seez) aka Berenice’s Hair. An open cluster is a collection of stars that formed around the same time in the same cloud of gas and dust. About 40 stars burn brightly in this cluster. You can read more about the Coma Star Cluster and Berenice’s Hair by following this link.

Second, if you have access to a telescope (four-inch diameter or larger would be best), you can delve into the burning heart of the Diamond. Locate Vindemiatrix (vin-duh-mee-AY-tricks), a star positioned nearly equidistant from the Diamond stars Denebola and Arcturus. If you draw an imaginary line between Denebola and Arcturus, Vindemiatrix will lie slightly to the left of that line, in the direction of Spica. Vindemiatrix, which like Spica is in the constellation Virgo the Maiden, is about the same brightness as Cor Caroli.

Now point your telescope midway between Denebola and Vindemiatrix. If you’re under a good black sky and you’ve dark adapted (avoided all white light) for at least 20 minutes, you should see some little glowing smudges. Unlike the Coma Star Cluster, which lies in the Milky Way, these objects lie beyond the Milky Way. These are galaxies in the famous Virgo Cluster of Galaxies; some are brighter and easier to spot than others. Give yourself plenty of time at the eyepiece to allow the faint light from these distant galaxies to accumulate on your retinas.

A galaxy is an immense gravitationally-bound system of stars. Approximately 2,000 galaxies, gravitationally bound to one another, make up the massive Virgo Cluster. The combined gravity from that enormous collection of galaxies even exerts an influence on other galaxy groups around it, including one very important to us: the group containing our home galaxy, the Milky Way. Someday, in the very distant future, our Milky Way may find itself pulled into the Virgo Cluster to become one of its member galaxies.

Imagine the hundreds of billions of burning Suns that make up one galaxy. Now multiply that image by 2,000. That’s a whole lot of firepower.

The Pond

Last week, we looked at one of my favorite spring star patterns, Three Leaps of the Gazelle. We learned that ancient Arabic star lore holds that the gazelle leapt from a spot in the sky known as the “Pond.” We can view that spot with the naked eye, as it is the well-known Coma Star Cluster in the constellation Coma Berenices (KOH-mah bare-uh-NIGH-seez).

Coma Berenices means Berenice’s Hair. Queen Berenice was a real person, a monarch of ancient Egypt. The Greek legend associated with Her Highness relates that she pledged her hair to the gods if they would keep her husband safe in battle. When he returned in one piece, she cut off her locks as promised and placed them in a temple. By the following day, they had disappeared. The court astronomer— apparently as politically astute as he may have been scientifically minded— determined that they had ascended to the heavens and could be seen as the spangled patch near Leo the Lion’s tail.

Let’s comb the sky for the queen’s tresses.

1) About an hour after your local sunset time, face south. If you don’t know the cardinal directions at your location and you don’t have a compass, make note of where the sun sets on the horizon. That spot is approximately west. Stand with your right shoulder to the west, and you’ll be facing approximately south.

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2) Tilt your head back and look at the zenith, the point in the sky that’s directly overhead. Near the zenith, or a bit below it toward the southern horizon, you should spot a fuzzy patch of stars. It will be slightly above and slightly east of Leo the Lion’s tail. This is the Coma Star Cluster (also known by its catalog designation Melotte 111)— what the Greeks saw as a bejeweled head of hair.

This star cluster is the most prominent naked-eye feature of Coma Berenices, and it’s the best way to tell when you’ve navigated into that particular constellation.

3) If you have binoculars or a small, wide-field telescope like the Starblast Astro, examine the cluster a bit more closely. Use your lowest power eyepiece (highest mm number) in your telescope. This is a really big object, so you don’t want to put much magnification on it.

Coma Star Cluster
© T. Credner & S. Kohle, AlltheSky.com

The Coma Star Cluster is an open cluster, a collection of stars that formed around the same time in the same nebula, or cloud of gas and dust. This cluster is believed to have around 40 member stars. You may want to think of them as a sort of family group.

Coma Galaxy Cluster
Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)

Coma Berenices doesn’t really have any other notable star patterns. Its other crowning glory, the Coma Galaxy Cluster, lies hidden to the unaided eye. The dense cluster contains thousands of galaxies, some of which can be observed by an amateur with a large-aperture reflecting telescope.

Astronomy Essential: The planets orbit the Sun at different speeds.

As the planets of our solar system orbit the Sun, they travel at different speeds. The closer the planet’s orbit is to the Sun, the greater its speed. The farther the planet’s orbit from the Sun, the slower its speed. Therefore Mercury, the nearest planet to the Sun, travels at an average orbital speed of 29.7 miles per second, whereas Neptune, the most distant planet, travels at a much slower average orbital speed of 3.3 miles per second.

The acceleration of planets that are closer to the Sun occurs because the closer the planet is, the greater the gravitational force the Sun exerts on it.

The “average orbital speed” is given here because, during its orbit, each planet speeds up when it is nearer the Sun and travels more slowly when it is far from the Sun. This variation in distance from the Sun occurs because the planets travel in elliptical orbits, not perfectly circular ones.

Three Leaps of the Gazelle

Between two of the boldest naked-eye star patterns in the spring sky lies a third more demure pattern that’s one of my personal favorites. It’s quite easy to spot when you know where to look, so let’s go stargazing, shall we?

1) About an hour after your local sunset time, face west. If you don’t know the cardinal directions at your location and you don’t have a compass, make note of where the sun sets on the horizon. That spot is approximately west— close enough for our purposes.

2) Tilt your head back and look at the zenith, the point in the sky that’s directly overhead. A little to the north (right), you should spy the distinctive seven-star pattern of the Big Dipper. The Big Dipper is an asterism, a recognizable star pattern, and it lies in the constellation of Ursa Major the Big Bear.

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3) Now look a little south (left) and west from the zenith. Look for the Sickle, the curved asterism that marks the head of Leo the Lion. The Sickle looks a bit like its namesake, the old-fashioned farm implement, or like a backwards question mark. Spot it? Great.

4) Look in the space between the curved top of the Sickle and the bottom of the bowl of the Dipper for three pairs of stars widely spaced from one another. Each pair is around the same distance from the other pairs, and the spacing between the two stars of each pair is around the same. In addition, the stars are all around the same magnitude of brightness. This similarity of pattern helps the little pairs to stand out from the stars around them.

These form the asterism known as Three Leaps of the Gazelle. The three star pairs all lie within the constellation of Ursa Major the Big Bear, and they mark three of the bear’s paws.

Ancient Arabic star lore relates that the gazelle was startled by the lash of the lion’s tail when it sprang from “the Pond,” what we know as the Coma Star Cluster in the constellation Coma Berenices (Berenice's Hair). You can spot the Pond naked eye from a dark site; it looks like a large, bright patch just off Leo's tail.

5) Starting at the Pond, the first set of hoofprints you come to are the stars Alula Australis and Alula Borealis. Alula (uh-LOO-luh) is from the Arabic for first leap; Australis and Borealis are Latin for southern and northern, referring to the respective position of each star.

The middle set of hoofprints are the stars Tania Australis and Tania Borealis. Tania (TAH-nih-yuh) is from the Arabic for second leap.

The final set of hoofprints are the ones farthest from the Pond. The northernmost star is Talitha (TAH-lith-uh), from the Arabic for third leap. Its companion has no traditional name, so we know it simply as Kappa, its star catalog designation.

Can you imagine the swift gazelle leaving behind those three pairs of watery hoofprints as it leapt between twin perils of lion and bear?

Astronomy Essential: The Milky Way galaxy belongs to a galaxy group.

The Milky Way, our home galaxy, is a member of a group of galaxies called the Local Group. It contains around 30 galaxies. The two that are closest to the Milky Way are called the Large Magellanic Cloud and the Small Magellanic Cloud. They are much smaller than the Milky Way and can be seen with the naked eye from the Southern Hemisphere.

Another well-known member of our Local Group is the Andromeda Galaxy, which can be seen naked eye from the Northern Hemisphere. The Andromeda Galaxy is the closest large galaxy to our Milky Way; it lies around two and a half million light years from Earth.

Galaxies throughout the universe tend to cluster into groups. The members of these galaxy groups interact gravitationally and sometimes collide.