Astronomy in a nutshell



If a flea paused in his epic journey through
the weave of the homespun trews of an ale-sodden
Hebrides husbandman, and bent its thoughts on the
grand design of the cloth, striving to grasp not just
the mechanics of the warp and weft of the loom,
but the overarching vision of the weaver, would
you be surprised?

If a single note in a symphony, battered and whirled
by woodwinds and violins, paused for a heartbeat
to consider and assemble a vision, not just of
the entire piece of music, but the conductor and
composer behind the oeuvre, would that raise an

Yet, astronomers, the carbon of their cellular
structures the product of some helpless exploding star
aeons ago, look out upon the entire cosmos, and ponder:
niggling away at countless points of light, in
search of a reason for every detail of its component
weave of light and sound; every aspect of its overall
structure bent by their basilisk gaze. All the while,
swept along willy-nilly on a tiny dust-mote planet,
scorched by an incandescent sun, gnawing on other
carbon life-forms for their sustenance, and quenching
their thirst with dihydrogen monoxide and knowledge
(and maybe beer as well).

The cosmos, looking down on this, can only gasp in
amazement at the unmitigated intrepidity, the
sheer audacity, of these tiny beings and their
grandiose goals and dreams. And that courage, that
vision, in a nutshell, is astronomy.

— G. P. Orris

Dwarf galaxy NGC 1569 image credit: NASA/Hubble

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).

Backyard Astronomy: November 2015


There’s not a lot going on in the November sky, but here are couple events you and your family can enjoy, with or without binoculars.

November 5,6: Taurids Meteor Shower. Meteor showers occur when the Earth moves through a cloud of debris left behind by a celestial object, like a comet. The Taurids are unusual in that they are debris from two objects: Asteroid 2004 TG10 and Comet 2P Encke. The meteors will appear to radiate from the constellation Taurus. As meteor showers go, this one is wimpy, with a modest 5-10 meteors per hour at its peak. The shower runs every year from September 7 to December 10, but will peak after midnight in the early morning of the 6th.

November 17,18: Leonids Meteor Shower. The Leonids are debris from Comet Tempel-Tuttle, and appear to radiate from the constellation Leo. As meteor showers go, this one is average with 15 meteors per hour at its peak. The shower runs every year from November 6th to November 30th, but will peak after midnight in the early morning of the 18th.

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.

Backyard Astronomy: October 2015

Here are several fun astronomical events you and your family can enjoy in the month of October — plus, a reminder for the lunar eclipse at the end of September. All you need is an inexpensive telescope or binoculars for most of these events, but some of them are viewable with the naked eye.

Reminder! September 27-28: Total Lunar Eclipse. A total lunar eclipse occurs when the Earth moves between the Sun and the Moon (see below). Unlike a solar eclipse, in which the Moon moves between the Sun and the Earth, you don’t need any protective eyewear to watch a lunar eclipse. During the eclipse, the Moon will gradually get darker, ultimately turning red in color. The lunar eclipse will be visible from the Americas, Europe, Africa, and parts of Asia. See here to determine visibility and times in your part of the world.


October 1: Comet C/2013 US10 Catalina. This comet was discovered on Halloween 2013. It could be bright enough to be visible with the naked eye in the Southern hemisphere by the beginning of October. By mid-November, it should be bright and visible in the North.

October 8: Draconids Meteor Shower. Meteor showers occur when the Earth moves through a cloud of debris left behind by a comet. The Draconids are debris from Comet 21P Giacobini-Zinnere, and appear to radiate from the constellation Draco. As meteor showers go, this one is kind of paltry with a modest 10 meteors per hour at its peak. The shower runs every year from October 6th to October 10th, but will peak in the early evening of the 8th.

October 16: Mercury at Greatest Western Elongation. Mercury will be at its greatest apparent distance from the Sun in the sky (~18 degrees). Mercury is best observed in the morning, just before sunrise.

October 21,22: Orionids Meteor Shower. The Orionids are debris from Comet Halley, and appear to radiate from the constellation Orion. As meteor showers go, this one is average with 20 meteors per hour at its peak. The shower runs every year from October 2nd to November 7th, but will peak the night of the 21st and early morning of the 22nd.

October 26: Venus at Greatest Eastern Elongation. Venus will be at its greatest apparent distance (~46 degrees) from the Sun in the sky. It’s a great time to observe Venus, because it’ll be highest in the sky in the morning, just before sunrise.

October 26: Conjunction of Jupiter and Venus. A conjunction occurs when two or more planets overlap, or appear very close together, in the sky. This is the second conjunction of these two planets this year (the closest occurred in July). In the early morning of the 26th, just before sunrise, Jupiter and Venus will appear within 1 degree of each other on the sky, which is the same distance as two Moon diameters.

October 28: Conjunction of Jupiter, Mars, and Venus. This is a rare three-planet conjunction, in which Jupiter, Mars, and Venus form a 1-degree triangle on the sky. It will be visible in the early morning of the 28th, just before sunrise.

Weekly Psalm 19: Mercury

Here is your weekly reminder of Psalm 19 — the planet Mercury.

Mercury is the smallest planet, as well as the planet closest to the Sun. It has a remarkably long day — a Mercury day lasts 88 Earth days — and a relatively short year (116 Earth days). Because of the peculiar ratio of its orbital period to its rotational period, a hypothetical observer on Mercury would experience only one day for every two years.

Mercury has no atmosphere, so the range of surface temperatures is extreme — -280 F during the night (the part of Mercury that faces away from the Sun) and up to 800 F during the day (the part of Mercury that faces toward the Sun).

Mercury has the most eccentric orbit in the Solar System, which means that out of all the planets, its orbit is the most like an ellipse. The part of its orbit closest to the Sun (the perihelion) precesses, which means Mercury’s orbit spirals around the Sun like a spirograph. Newton’s version of gravity could account for some of this precession, but not all of it. The reason for the discrepancy remained a mystery for centuries, until Einstein formulated his General Theory of Relativity, which explained the precession in terms of the way the Sun warps space around Mercury.

Image credit: NASA.