Supernovae: Cosmic Fireworks

A supernova is a spectacular explosion of a massive star. Not very. Astronomers believe that about two or three supernovas occur each century in galaxies like our own Milky Way. Because the universe contains so many galaxies, astronomers observe a few hundred supernovas per year outside our galaxy. Space dust blocks our view of most of the supernovas within the Milky Way.

A supernova is a magnificent, luminous explosion that marks the end of a massive star’s life. These events are relatively rare: only about two or three supernovae occur each century in a galaxy like the Milky Way. Astronomers typically detect only a few hundred supernovae outside our galaxy every year.

Given that the observable universe contains an estimated 2 trillion galaxies, why do astronomers register so few supernovae per year? The reason is that most supernovae occurring in the universe are too faint to be observed. They may be obscured from our view by cosmic dust, or they may be located too far away for present-day telescopes to detect.■

Sources

1. What Is a Supernova? | NASA Science
2. How Many Galaxies Are There? | Space
3. Cosmic census of galaxies updated to 2 trillion | Science News
4. How many galaxies are in the Universe? | BBC Science Focus
5. How Many Galaxies Are There in the Universe? | Sky & Telescope

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• Cover Image: Snapshot of “Supernova with Expanding Shell” by Michael McClare and Dana Berry, Goddard Space Flight Center; available in the NASA Image and Video Library.

Chilling Resilience: How Frogs Survive the Cold Winter

Animals have a variety of ways to cope with adverse environmental conditions. Many utilize dormancy—a prolonged period of inactivity and fasting—to survive winters when temperatures often drop below freezing.

Frogs, along with other cold-blooded amphibians, lack the ability to regulate their body temperature internally. Thus, they have developed clever methods to conserve energy when their bodies cool significantly during winter brumation, a process similar to hibernation in mammals.

Clearing the Air: Tree Planting Won’t Solve Air Pollution

Undoubtedly, trees play an important role in reducing air pollution in urban areas. However, their contribution alone is not sufficient. While trees are generally beneficial, they can also have negative effects. In some cases, they hinder the dispersion and transport of air pollutants and may even emit gases that exacerbate air pollution.

Checking In? Check for Bed Bugs First

The last thing you want after returning home from a business trip or vacation is to discover unwelcome guests—bed bugs—that you brought with you. They are found worldwide, from North and South America to Africa, Asia, and Europe, even in unexpected places like five-star hotels and luxury resorts. Therefore, the first thing you should do after checking into a hotel room is to inspect it for bed bugs.

Spiral Arms: Stellar Traffic Jams

The sprawling spiral arms observed in spiral galaxies aren’t structural components. Scientists believe that these arms represent enormous traffic jams—areas of increased density formed by the combined effects of differential rotation and gravitational clumping of galactic material.

Weighty Matters: Earth’s Gravitational Variations

Looking to shed a few pounds quickly? Consider climbing Mount Everest. At the summit of the world’s tallest peak, you’ll weigh approximately half a percentage point less than at sea level (assuming you haven’t lost mass during the ascent!). If mountain climbing isn’t your cup of tea, hop on a scale at the North Pole, then relocate to Kenya or Ecuador. You’ll find yourself weighing slightly less at the equator— about one-fifth of a percentage point less, to be precise.

Moonlight Sonata: The Rhythm of Eight Lunar Phases

As the Moon completes its orbit around Earth, its appearance transitions from invisibility to a brightly illuminated, near-circular disk. These changes are known as the “phases” that comprise a lunar cycle. Each cycle lasts, on average, 29 days, 12 hours, 44 minutes, and 3 seconds in Earth time and consists of eight phases: four primary and four intermediate.

When we observe the Moon with approximately half of its surface illuminated, it’s commonly referred to as a “half moon.” However, this term is astronomically inaccurate.

The Scorched Aroma of Lunar Dust

Does the Moon smell like cheese? Not quite.

When Apollo 11 astronauts completed their moonwalk and returned to the Eagle lunar lander, they described the scent as resembling spent gunpowder. This odor emanated from the lunar dust that coated their spacesuits, equipment, and the lunar samples they brought back on board.

The Magnifying Power of Gravitational Lensing

Wouldn’t it be nice to have magic glasses that allow you to see through solid objects? (On second thought, maybe it’s not such a good idea. You wouldn’t want a stranger watching you take a shower.)

For scientists, there’s no need for magic glasses. A natural phenomenon called “gravitational lensing” allows astronomers to do just that: see celestial objects hidden behind other objects.

Planet or Not?

What exactly are planets, the objects in the sky the ancient Greeks called “wanderers?” There are various ways to define them.

In 2006, the International Astronomical Union (IAU), the authority responsible for naming celestial objects, established the official definition of a planet as a celestial body that meets these three criteria: 1) orbits the Sun, 2) has sufficient gravity to assume a nearly round shape, and 3) has cleared its orbital path of other celestial bodies of similar size. Although some astronomers find this definition inadequate and point out inconsistencies in its application, it is now widely accepted as the concept defining what type of object in our solar system deserves to be called a “planet.”