Weekly Psalm 19: The Heart of Cygnus

Here is your weekly reminder of Psalm 19 — the heart of Cygnus.


Also known as IC 1318 or the Sadr region, this nebula lies at the heart of Cygnus the Swan, a summer constellation in the Northern hemisphere. IC 1318 is an emission nebula, ionized by the radiation from a nearby hot star.

The bright star on the left is Deneb (Alpha Cygni) and the bright star on the right is Sadr (Gamma Cygni), neither of which are actually part of the nebula, but lie partway between Earth and IC 1318. These stars are clearly visible to the naked eye, but the emission nebula is too faint to be seen without long exposures on a telescope.

The pink patches are ionized hydrogen gas, and the dark streaks are dust-infused gas blocking visible light from view.

Image credit:Bill Mark.

Weekly Psalm 19: Bode and the Cigar

Here is your weekly reminder of Psalm 19 — the galaxy pair, M81 and M82.


This galaxy pair is part of the M81 group, a collection of 34 galaxies that are all gravitationally bound to each other. These two galaxies (click the image to enlarge it) are particularly strongly attracted to each other, which has triggered some extreme activity in both.

The spiral galaxy on the left is M81, and is also referred to as Bode’s Galaxy, after J.E. Bode, who discovered it in the 18th century. Bode’s Galaxy has an active black hole in its center weighing in at 70 million times the mass of the Sun. The gigantic black hole is feeding on gaseous material that has spiraled down to the center of the galaxy, which causes it to shine very brightly. The galaxy on the right is M82, and is sometimes called the Cigar Galaxy because of its cigar-like shape, which is due to its gravitational interaction with M81. This interaction has triggered massive star formation in M82.

The galaxy pair appears in the Ursa Major constellation, and is relatively nearby at 12 million light-years away, making it a favorite of both professional and amateur astronomers. The M81 Group is a neighbor to the Local Group, which contains the Milky Way, and the two groups are part of the much larger Virgo Supercluster of galaxies.

Image credit:Anttler.

Weekly Psalm 19: Spiral galaxy NGC 2841

Here is your weekly reminder of Psalm 19 — spiral galaxy NGC 2841.


Click on the image to appreciate its full grandeur.

Such a boring name for such a beautiful object. German-British astronomer William Herschel discovered NGC 2841 in the late 18th century, although at that time he wouldn’t have known what he was looking at. Astronomers at the time categorized these indistinct objects as “spiral nebulae” and thought they resided inside of the Milky Way. By the 1920s, astronomers realized they were looking at “island universes,” what we now refer to as galaxies, that are well beyond the Milky Way.

NGC 2841 is, like our galactic home, a spiral galaxy. However, it’s about 50% larger and its arms are “flocculent” or patchy and more tightly wound than the Milky Way’s. At 46 million light-years away, this galaxy is close enough to us that the Hubble Space Telescope was able to snap this magnificent view of its interior. Its golden-yellow nucleus contains a dense population of very old stars, while its arms are punctuated by bright blue dots and glowing pink hydrogen clouds indicating regions where new stars are forming. The dark swirls in the galaxy’s patchy arms are comprised of dusty gas that blocks visible light from view. If you have sufficiently dark skies and a large-ish telescope, you should be able to see this galaxy as an indistinct patch of fuzz in the Ursa Major constellation.

Image credit: NASA, ESA, and the Hubble Heritage (STScI / AURA) – ESA / Hubble Collaboration.

The grand ballroom of the universe

There are a lot of galaxies in the universe, and like people on a crowded dance floor, they sometimes collide. The time it takes for the full collision to unfold is hundreds of millions of years, so what we see when we observe colliding galaxies with our telescopes are really just snapshots of particular moments during the collision. To try to understand the physics of galaxy collisions, astrophysicists often create sophisticated supercomputer simulations that match our observations of different stages of actual collisions; but instead of taking a hundred million years to play out, we can watch the whole thing happen in the space of minutes.

I love watching simulated galaxy collisions, and I think you’ll find them fascinating, too. It’s as though two galaxies decide to become partners in some cosmic ballroom dance. Even though the collisions are destructive, there is something so graceful and elegant about them that I always hear Mozart in my head as I’m watching.

I wanted my astronomy students to appreciate all this, so a few years ago I put together a video compilation of three galaxy collision simulations by astrophysicists at Case Western Reserve University and set them to one of my favorite Mozart symphonies. The simulations are sometimes paused mid-collision so that the “camera” can pan around to give us a look from different angles. Following each simulation there’s an image of an actual galaxy collision of that type so you can see how well the physics of the simulations matches what we observe in the universe.


Weekly Psalm 19: The Bubble Nebula II

I’ve had requests to bring this feature back, which I am happy to do. So, here is your weekly reminder of Psalm 19 — the Bubble Nebula, up close and personal.


Click on the image to fully appreciate its grandeur.

The Bubble Nebula is a shell of gas surrounding a massive, extremely hot star that is 15 times the size and 40 times the mass of our Sun. Stellar winds from the star push the bubble of gas out, while radiation from the star excites the gas in the bubble and causes it to glow.

The nebula resides in a giant molecular gas cloud in the constellation Cassiopeia, and is about 7,100 light-years away. The Bubble itself is 3 – 5 light-years in size, which, if you could see it with your naked eye, is half the apparent size of the full Moon on the sky.

This image is a composite of images of the Bubble Nebula taken with the Hubble Space Telescope this year, created by NASA to commemorate the 26th anniversary of Hubble’s launch. The nebula is imaged separately with different filters, and then combined with false colors to create this compelling final product. What you’re seeing here is radiation from excited hydrogen (red), oxygen (green), and sulfur (deep red) atoms.

Image credit: NASA, ESA, Hubble Heritage Team (STScI / AURA)

Weekly Psalm 19: Arp 274

Here is your weekly reminder of Psalm 19 — colliding galaxies, Arp 274.


Galaxy collisions are a testament to the strange way in which space is scaled. The universe is a relatively crowded place on the galactic scale, which is why these collisions are fairly common. But when galaxies crash into each other, the stars in them are so far apart from each other that the stars themselves usually don’t collide.

Think of it this way. If you were to draw a 1 cm dot that represented the Sun, the nearest star to the Sun (Alpha Centauri, ~4 light-years away) would be a slightly larger dot about 400 km away. That’s how much space there is between the stars.

Now, if you were to draw a 1 cm dot that represented the Milky Way Galaxy, the nearest galaxy to ours (Andromeda, ~2.5 million light-years away) would only be 25 cm away.

That’s why galaxies often collide, but stars usually don’t. However, the gas and dust that is inside galaxies does collide, and this leads to a brief period of intense star formation as the galaxies gravitationally tear each other apart. Once this violent dance settles down, a newly formed galaxy remains.

Galaxy collisions take hundreds of millions of years to play out, so what we’re seeing with images like the one above are cosmic snapshots of collisions. Astrophysicists use supercomputer simulations to hugely speed up the process and explore what a full collision would look like.

Image credit: NASA, ESA, M. Livio (STScI) and the Hubble Heritage Team (STScI/AURA).

Weekly Psalm 19: Enceladus

Here is your weekly reminder of Psalm 19 — Saturn’s moon, Enceladus.


Enceladus is the sixth-largest of Saturn’s 62 moons. At 500 km diameter, it is dwarfed by Saturn’s largest moon, Titan (5,100 km) and Earth’s Moon (3,500 km). It was discovered in the late 18th century by the German-English astronomer, William Herschel, whose son, John, named it. Not much was known about Enceladus until the Voyager missions studied the moon in the 1980s. The Cassini mission followed in 2005 to study Saturn and its moons in greater detail. The above image was taken during this latest mission.

The surface of Enceladus is comprised of clean ice (as opposed to “dirty” ice, which contains rock, dust, and organic compounds) that reflects most of the sunlight that reaches it. Enceladus has an active surface, with over 100 geysers spewing water vapor into the rings of Saturn. Last year, Cassini found evidence of a subsurface ocean beneath the icy surface. The Cassini spacecraft is scheduled to fly through one of Enceladus’ geyser plumes in the hope that it will reveal the chemical makeup of its liquid ocean.


Image credit: NASA/JPL.

Weekly Psalm 19: Milky Way Galaxy

Here is your weekly reminder of Psalm 19 — our galactic home, the Milky Way.


This graceful arch across the sky is our home, as seen from within the Galaxy itself.

Have you ever wondered why it’s called the Milky Way? The ancient Greeks called it the “milky circle,” because they thought it looked like milk spilled across the sky. (The Greek word for “milky” is galaxias, which makes the name Milky Way Galaxy a little tautological.)

The Milky Way is a spiral galaxy, about 100,000 – 150,000 light-years across. It contains an estimated 200-400 billion stars, including our Sun. The Solar System is located about 30,000 light-years away from the center of the galaxy at the edge of the Orion arm (see image below). Incidentally, did you know there are stars between the arms in a spiral galaxy? Quite a few actually, but many of them are not visible because they are dimmer than the very luminous massive stars that tend to bunch up in the arms.


The Milky Way has a supermassive black hole in its center, just like every other galaxy that’s been observed. It weighs in at about 4 million times the mass of the Sun, which may sound like a lot, but is kind of “meh” as far as supermassive black holes go (some of these giant black holes tip the cosmic scales at 10 billion times the mass of the Sun). If you wanted to look in the sky in the direction of this black hole, called Sagittarius A*, you would look at the Milky Way in the direction of the constellation Sagittarius. You wouldn’t see anything that suggests a black hole, especially because it’s smaller in size than Mercury’s orbit around the Sun, but it’s sort of fascinating to know that it’s there nevertheless.

Fraser Cain explains what we’re actually looking at when we observe the Milky Way in the sky:


Milky Way image credit: Steve Jurvetson. Milky Way schematic credit: Sky & Telescope magazine.

Weekly Psalm 19: LH 95

Here is your weekly reminder of Psalm 19 — star forming region, LH 95.


LH 95 is a stellar nursery, a region in which star formation is actively occurring, in the Large Magellanic Cloud (LMC). The LMC is a small, irregular satellite galaxy orbiting the Milky Way, but visible only from the Southern Hemisphere. LMC’s close proximity allows detailed views of stars and nebulae in a galaxy outside of our own.

Astronomers have identified thousands of baby stars in their initial stages of development in this nursery, providing a detailed picture of how star formation in the early Milky Way likely occurred. The blue color in LH 95 is starlight from very large, hot stars reflecting off hydrogen gas. This glowing gas is surrounded by the cold, dusty molecular gas out of which new stars form.

Image credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration.

Weekly Psalm 19: Supermoon Lunar Eclipse

Here is your weekly reminder of Psalm 19 — a “supermoon” lunar eclipse.


Last Sunday, many of us were treated to a rare combination of a lunar eclipse and a “supermoon.” A supermoon occurs when a full moon phase coincides with the Moon being at its closest point in its slightly elliptical orbit around the Earth, making our lunar companion look slightly larger (~14% in diameter) in the sky than normal. What really makes a supermoon “super” is its increased brightness — owing to its closeness to the Earth, a supermoon is 30% brighter than a regular full moon.

A lunar eclipse occurs when the Earth moves between the Sun and the Moon, blocking out the sunlight that normally reflects off of a full moon.


When I teach introductory astronomy, the students who are really paying attention will ask why we don’t always get a lunar eclipse during a full moon phase. The answer is, the plane of the Moon’s orbit (outlined with the green circle above) is slightly tilted with respect to the Earth’s orbital plane (outlined in blue), so that most of the time the Earth does not block light coming from the Sun. Rarely, we’ll get the Sun, the Earth, and the Moon lining up when the Moon is in the Earth’s orbital plane, and that’s when we experience a lunar eclipse.

The next time a supermoon will coincide with a lunar eclipse is in the year 2033.

Supermoon lunar eclipse photo credit: Dina Rudick (Boston Globe). Lunar eclipse schematic credit: Wikipedia.