10 Fascinating Facts about the Star Sirius

Stars are fascinating. With so many of them, the starry night has inspired philosophers and scientists for thousands of years of human history. Stars come in many shapes, colors, and sizes. While many stars are spherical,.others, like Vega, are ellipsoids because of distortions due to rapid rotation or a multi-star system’s gravitational complexity. In fact, our Sun is a spherical yellow dwarf G-class star.

When it comes to the night sky, Sirius—also known as the “Dog Star”—is the biggest star in our local neighborhood as part of the constellation Canis Major. A beautiful bright white star, Sirius has been known since ancient times as one of the most prominent objects in the sky. Here are some interesting facts about Sirius to enlarge and entertain our minds.

Related: 10 Startling Facts About the Asteroid That Killed the Dinosaurs

10 A Very Large Star

Imagine a large cherry tomato. Then, put a lime next to it. The cherry tomato is an approximation of the Sun. The lime is an approximation of Sirius’s size compared to the cherry tomato Sun. Amazingly, Sirius is a higher luminosity and larger-sized star than the Sun. Although, at night, it seems that the Sun is the largest star, that is only because of perspective as seen from Earth. Earth is the third planet from its star, so naturally, the Sun looks much brighter than if Earth were orbiting another star.

The ancients interpreted Earth as the center of the universe because of perspective. What seemed to be true was true to them. New modern data from parallax measurements of stars like Sirius have changed scientists’ beliefs about the size of the Sun compared to other stars.^[1]

9 Hotter Than Our Sun

Like many things in life, the universe is easier to understand when the objects that are observed in it are classified and organized well. Astronomers use a special classification system to describe the temperatures of stars. This classification system is known as the Morgan-Keenan system. This system assigns non-alphabetical order letter values from hottest to coldest to describe all stars by temperature value.

The system ranks stars from an older system developed at Harvard University in the following sequence from hot to cold: O, B, A, F, G, K, M, L, T, Y. Sirius is an A-class star that has an average surface temperature of 9,940 Kelvin or 17,432.6°F (9,667°C). For comparison, our Sun has a surface temperature of 5,772 K or 9,930°F (5,500°C). Such a high temperature is hot enough to melt all elements into a plasmic vapor.^[2]

8 Sirius’s Dwarf Star Companion

Sirius, specifically Sirius A, has a white dwarf companion known as Sirius B. Sirius B is a compact object orbiting its giant, well-known partner. It is the nearest known white dwarf star to our solar system. That makes Sirius B a useful object for research on white dwarf planets. White dwarves are thought to be the cores of medium- and small-size stars after they go nova and explode.

It is probable in ancient times that Sirius B was a larger star similar to Sirius. If true, the older Sirius would have been even brighter, with two large stars shining forth in the night sky while orbiting each other. Such a massive stellar duo would have made an enormously bright star in Earth’s distant past. Perhaps the dinosaurs would even have cast shadows under the double Sirius star system’s light at night.^[3]

7 While Bright, Sirius Is Light Years Away

The enormous distance between stars is hard for the human mind to grasp. Thankfully, mathematical ratios can be developed to give analogies for the distances. Hypothetically, if Earth was 1 mile from the Sun, Sirius would still be an astounding 335,540 miles (540,000 kilometers) away from the Sun. That is more than the distance between the Earth and the Moon.

In reality, Earth is about 93,000,000 miles (150,000,000 kilometers) away from the Sun. Sirius is about 50,500,000,000,000 miles (81,000,000,000,000 kilometers away from the Sun. The huge distance between Sirius and the Sun means that traveling to Sirius is impossible with current technology and human lifespans. However, that hasn’t stopped people from imagining the possibilities.

Some sci-fi writers have proposed that interstellar travel could be made possible by generation or hibernation ships. A generation spaceship is a concept where the people who get on the spaceship are not those who get off at the star. They are the grandparents of the people who finally reach a star like Sirius. A hibernation ship to Sirius is even more hypothetical. Put all the astronauts to sleep until the starship arrives at its destination.

These concepts are unlikely because of their expense and difficulty to implement. Unfortunately, that means humans will probably never visit Sirius.^[4]

6 More Massive Than Our Sun

Sirius is almost exactly twice the mass of the Sun. The Sun has a mass of about 2 nonillion kilograms. That is 333,000 times the mass of planet Earth. Sirius has a mass of about 4 nonillion kilograms. A nonillion is 1, followed by thirty zeros. That is a lot of hot plasma blazing out there in outer space. Thankfully, Sirius is very far away; otherwise. our poor planet Earth would be fried orbiting such a big star. A 4-nonillion-kilogram mass star is not necessarily the best next-door neighbor for a life-bearing planet like Earth to have.

The gravitational field of Sirius is stronger, so any potential comets passing by would be swooped up from a greater distance than with the Sun. Many astronomers believe the Sun has an Oort cloud extending for about 1 light year beyond the solar system. The greater mass of Sirius means that its gravity field has the potential to capture comets farther out than the Sun can. However, no evidence has been found for an Oort cloud around Sirius to date.^[5]

5 No Known Exoplanets

Despite a fairly rigorous search in 2021, which involved Sirius’s white dwarf companion star, no exoplanets have been found orbiting in the Sirius star system. That does not mean such Siriusian exoplanets do not exist. It just means astronomers currently do not have the instruments or telescopes powerful enough to see planets smaller than Jupiter around Sirius. It is challenging to see planets orbiting other stars.

To photograph such exoplanets, the parent star’s light must be blotted out by a filter. That is a method that has worked to visualize large exoplanets around other stars like Fomalhaut. The Fomalhaut system, unlike Sirius, has a confirmed exoplanet named Fomalhaut b. More powerful telescopes must enter service to confirm for sure whether or not the Sirius system has exoplanets. The current consensus is that Sirius does not.^[6]

4 The Brightest Star

Because of its size and relative proximity to the Milky Way Galaxy, Sirius is the brightest star visible at night from planet Earth. The ancients used Sirius to calibrate their calendars. This was particularly important in ancient Egypt. Ancient Egyptians used the star Sirius’s rising at certain times to plan when the Nile River would flood so that they could plant their crops at the right time.

Before the invention of the Gregorian calendar, the cycle of Sirius in the night sky helped the ancient Egyptians to conclude that the solar year is about 360 days. The actual solar year is 365.24 days, so they were not that far off, and Sirius gets the credit for helping the Egyptians figure out when to plant their crops.^[7]

3 Sirius Is Moving Toward the Solar System

Because of orbital mechanics acting within the Milky Way Galaxy and the large-scale gravitational forces acting between the stars, Sirius is approaching the solar system at 3.42 miles per second (5.5 kilometers per second). Astronomers predict that, at Sirius’s closest approach to the solar system, it will be only 8.18 light years or 47.9 trillion miles (77 trillion kilometers) away.

Astronomers used data from the Hipparcos satellite to develop this prediction. Astronomers predict that Sirius’s close approach will occur within about 46,000 years. According to current research, there is no indication that Sirius will get dangerously close to the solar system.^[8]

2 Ptolemy Mysteriously Described Sirius as a Red Star

Most modern astronomers dispute the claim that Sirius was once a red star because ancient Chinese astronomers reported Sirius as white. This is the currently accepted model. Sirius has been a white star system for all of human history. Nonetheless, Claudius Ptolemy made the strange claim that Sirius was red around AD 150.

If true, it would alter the model for how rapidly stars age. The explanation for why Ptolemy reported Sirius as a red star could be that the white dwarf Sirius B used to be a red giant orbiting Sirius A. Hypothetically, such a situation would have caused the whole double star system called Sirius to appear reddish in ancient times.^[9]

1 Its Brightness Outshines Our Sun

Sirius would appear much brighter than the Sun if it was as close to Earth as the Sun. Although Sirius is not much larger compared to the Sun, it is substantially hotter and, therefore, much brighter than the Sun. Sirius being 25 times brighter than the Sun means possible exoplanets orbiting Sirius would be scorched, making it very unlikely that astronomers will ever discover lifeforms in the Sirius system, even though some sci-fi novels may suggest otherwise.

For life to exist on an exoplanet orbiting Sirius, such an exoplanet would have to be much farther out from Sirius than planet Earth is from the Sun, or the alien lifeform would need to have adapted to living underground and dealing with extreme temperatures.^[10]