Planetary extravaganza 2020 featuring Mars


By Tom Burns - Stargazing



We are in the midst of an astronomical extravaganza, at least as far as naked-eye planets are concerned.

For Mercury, the hardest of the planets to see because it is the closest to the sun, you’ll have to wait until early to mid-November. Only then will it be far enough from the sun’s glare to be briefly visible in the morning sky before the rising sun spoils the view.

In the morning sky, Venus shines brightly in the east. If you go out during morning twilight and look in that direction, you won’t have to ask which “star” is Venus. A small telescope reveals that Venus has phases just like Earth’s moon. Right now, the planet is about 75% illuminated. It looks like about a quarter of it has been shaved off.

In the early evening, Jupiter dominates the sky. Go out as the sun is setting, and look low in the SSW. Then wait until Jupiter pops into view. Point binoculars at Jupiter when the sky gets fully dark, and you might be able to spot from one to four of Jupiter’s four brightest moons, called the Galilean moons, lined up around the planet.

Then wait a little longer, and you’ll see much dimmer Saturn appear out of the growing darkness to the left and slightly up from Jupiter. Binoculars won’t help you here. You’ll need at least a small telescope to see Saturn’s famous rings.

Now, wait a bit longer. Off to the southeast, Mars will rise. The Red Planet will appear as a blazingly bright point of yellow-red light. Right now, it outshines Jupiter, the fourth brightest object in the sky after the sun, moon, and Venus.

You can also see Pluto — if you have a huge telescope with computer control and tracking, an excellent set of star maps, a good set of eyes, and an iron will. It sits about halfway between Jupiter and Saturn. Even in a large, observatory-sized telescope, Pluto will be the faintest “star” in the field of view. It will be the one that’s not on your star map.

Add Neptune to the list if you have a telescope. It is visible as a tiny disk of blue-green light in the constellation Aquarius.

Uranus, which rises just after Mars, is in the constellation Aries, the Ram. If you know exactly where to look and your sky is dark and rural, Uranus is just barely visible to the unaided eye. In a telescope, don’t expect more than a bluish dot.

I have observed all of the original planets in one night but once in my life. After I saw Venus in the morning, I looked down at the Earth beneath my feet and realized that I had seen them all in that exhilarating moment. It was a moment that I shall never forget. I hope that someday you will be able to do the same.

For now, pay careful attention to Mars. The Red Planet is so bright right now because we are experiencing what astronerds like me call a Martian opposition.

To understand why Mars is so bright, we need to think about the orbits of the two planets around the sun. Earth is the third planet in orbit, and Mars is the fourth. It is as if they are in the race around the sun, a race that Mars can never win.

For one thing, Mars has farther to go because it averages 132 million miles from old Sol. Earth has the inside track at 93 million miles away from the sun.

Also, because of Earth’s relative proximity to the sun and the sun’s gravity, Earth moves faster at an average of 67,000 miles per hour. Mars pokes along at about 54,000 miles per hour.

The result is that Earth takes about 365 Earth days to make one orbit. Mars takes 687 days.

Every 26 months or so (or 779.94 days to be nerdishly precise), Earth catches up to Mars, and they are lined up with the sun. Mars is “opposed” to the sun from Earth. That’s where we get the term “opposition.”

The result of all this is that Mars is closest to Earth every two years and two months or so. Its proximity makes Mars appear brighter from our Earthly vantage.

Thus, Mars will look very bright during the rest of October. It will also look larger than usual, a fact that our poorly configured eyes cannot discern. But you’d better believe that amateur telescopists the world round are scurrying to their telescopes to take a look.

This opposition is a pretty good one, but not the best. Oppositions may happen relatively frequently, but some oppositions are particularly good because of the nature of planetary orbits.

Planets do not orbit the sun in perfect circles. They travel in stretched-out circles called ellipses. For that reason, sometimes Earth is a little closer to the sun and sometimes a little farther away. The same goes for Mars.

When Earth is closest to the sun and Mars is farthest away, the two planets can be as many as 67 million miles from each other at opposition. The most recent distant opposition was in 2012. Frustrated telescopists saw only a tiny disk because Mars was 62.65 million miles away.

When Earth is farthest from the sun and Mars is closest, the distance between the two planets can shrink to about 34 million miles.

Such close oppositions happen only every 15-17 years. This is not one of them, but it’s close. (The next really close opposition won’t occur until 2035.)

Here’s another oddity caused by the orbits of the planets. Opposition occurs on Oct. 22. However, Mars was actually at its closest to Earth on Oct. 6. Again, the elliptical nature of the orbits is partly to blame. The Martian orbit is slightly more elliptical than Earth’s orbit.

Add to that factor the tilts of the orbits around the sun. Most people imagine the orbits of planets on a single plain — like marbles rolling around on a plate. Instead, their orbits are tilted from the plate by varying degrees.

Earth’s and Mars’ orbits are only slightly tilted with respect to each other, but the result is that Mars was at its closest — and therefore its brightest — 16 days before the planets were lined up in their opposition.

This time around, Mars is only a tad bit fainter and smaller than it was during the last very close opposition in 2018. Extra-close oppositions bring Mars within at least 37 million miles of Earth. This time around, Mars is 38.57 million miles away at its closest.

Even slight shifts in the Mars/Earth distance makes a big difference in how Mars looks in a telescope. It’s a dinky little planet at about 4,000 miles wide. That’s only about twice the diameter of Earth’s moon. At opposition this time around, Mars is more than 155 times farther away than the moon.

However, during the 2020 opposition, the planet also gets much higher in the sky. Also, it appears in the constellation Pisces, which is a relatively faint constellation. The lack of bright background stars will make it look even brighter.

Let’s face it. The hype surrounding Martian oppositions is unwarranted. Even under the best of circumstances, Mars is no big deal in a telescope. Also, because of the pandemic, nobody is going to let you look through theirs anyway. So enjoy its brilliance with the binoculars you were born with — your own two eyes.

I must confess that I view every Mars opposition with a certain degree of trepidation.

During the last extremely close opposition in 2003, Mars briefly approached within 34.62 million miles of Earth. That’s nearly as close as it gets.

In August 2003, the Internet was rife with sometimes stunning misinformation. Most notably, the rumor went around that Mars would appear “as big as the full moon” on the night of the closest approach.

Of course, if Mars approached close enough to appear as big as the full moon, the gravitational effects would be disastrous to life on planet Earth. As far as I can tell, we’re still here.

Up to my retirement from Perkins Observatory a couple of years ago, every year in August, I received by email the same dinky “Mars Big as the Full Moon!!!” slide presentation at least once. That’s the trouble with the Internet. Bad information never really goes away.

Weird theories attach themselves to every close opposition. Also, Mars has been the subject of strange speculation throughout history.

Next week, I’ll resurrect some of those odd speculations out of their astronomical graves.

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By Tom Burns

Stargazing

Tom Burns is the former director of the Perkins Observatory in Delaware.

Tom Burns is the former director of the Perkins Observatory in Delaware.