One of the joys of astronomy is getting to see the universe with your own eyes. Most amateur astronomers know the magnificent feeling of looking at the moon through a telescope, picturing it drifting through empty space as it revolves around the Earth. After looking at the rocky, pockmarked surface of the moon, they want to cast their gaze out towards the planets of our solar system.
Mars and Venus are Earth’s most immediate neighbors, but why not start your observations with the planet that’s closest to the sun? Mercury can be a challenging planet to catch sight of because it hides behind the sun for most of the year. However, with the right knowledge, even a beginner astronomer can spot the smallest planet in the solar system. Read on for everything you need to know.
When Is Mercury Visible?
Some planets, like Uranus, are difficult to see through a telescope because they shine so dimly in the sky. That’s not the case with Mercury. At its brightest, Mercury shines at a magnitude of -1.9. That means Mercury is sometimes brighter than the brightest star in the sky, Sirius.
The challenge with spotting Mercury through a telescope is its proximity to the sun. Mercury doesn’t stray far enough from the sun to be visible at night, but during the day, looking for Mercury with a telescope can seriously damage your eyes. A handful of times through the year, when Mercury has drifted as far from the sun as possible, the planet can be seen at twilight.
In 2021, there will be six windows of opportunity for an amateur astronomer to get a look at Mercury. They are:
January 10th to January 31st – Through most of January, Mercury can be seen in the early evening after sunset.
February 28th to March 20th – For this period of time, Mercury will show itself in the mornings, moments before sunrise.
May 3rd to May 24th – During these weeks, Mercury will be visible in the evening, just as the sun is dropping below the western horizon.
June 27th to July 16th – In this window, Mercury will peak above the horizon just before the sun rises.
August 31st to September 21st – The ideal time for spotting Mercury in this window will be just after sunset.
October 18th to November 1st – Once again Mercury will be an early bird, drifting over the horizon just before sunrise.
When is Mercury at its brightest in the sky?
During the windows of time listed above, Mercury will reach a point known as “maximum elongation”. At that point, Mercury will be as far as it can get from the sun. On those days, Mercury will be the easiest to spot, and an astronomer will have more time to look at the planet before the sun’s glare washes it away.
Even at maximum elongation, Mercury is never more than 27.3 degrees from the sun. For reference, that’s about the distance between your pinky and thumb stretched apart. Mercury will be at maximum elongation for exactly one day in each window of visibility. In 2021, those days are:
January 24th – Mercury will be 18.6 degrees from the sun.
March 6th – Mercury will reach its farthest elongation from the sun of the year, at 27.3 degrees.
May 17th – Mercury will be 22 degrees from the sun.
July 4th – Mercury will be 21.6 degrees from the sun.
September 13th – Here Mercury will stretch to 26.8 degrees from the sun.
October 25th – Mercury will be 18.4 degrees from the sun.
When can you see Mercury through a telescope?
If you’re trying to see Mercury through a telescope, you should do so on one of the days of maximum elongation listed above. While Mercury is visible on other days, you should practice on a day of maximum elongation. You want to be careful to stop looking through your telescope well before the sun’s glare creeps over your view of the planet, so the days of maximum elongation will give you the most time to find and observe Mercury.
How To Get The Best View of Mercury
Before trying to look at Mercury through a telescope, you should make plans for your observation. Looking through star charts in a book or via an astronomy app on your phone can help you know approximately where Mercury will sit in the sky on your observation day. Mercury will always be very close to the horizon. Its highest points above the horizon will be during maximum elongation in March, at 12 degrees, and October, at 10 degrees.
When you’re looking for Mercury, remember that you are looking through the thickest part of the Earth’s atmosphere. Because of that, Mercury’s shine will appear to twinkle in the sky. If you’re looking through a pair of powerful binoculars, you should be looking for a light pink, almost white, glow.
It’s also useful to remember that because Mercury is so close to the sun, from our perspective it goes through phases, just like the moon. Sometimes Mercury will only be a crescent in the sky, but at other times it will be full and incredibly bright.
If you’re looking for Mercury during one of its early morning windows of visibility, you’ll want to wake up very early. The sun’s light can quickly blot out the planet’s visibility. Be looking towards the eastern horizon at least an hour before sunrise for your best chance to catch Mercury.
If you’re looking during one of Mercury’s evening windows of visibility, you should get set up before sunset. You’ll want to start your search just as the sun dips below the horizon. You should have about an hour to get a good look at the planet.
How to find Mercury with your phone
You can use your phone to help you get prepared to spot Mercury. Both the App Store and the Google Play Store have some excellent stargazing apps that can help you plan your observations. Some of the best are SkyView, Star Chart, and Google Sky, and they won’t cost you much at all.
How to Find Mercury In A Telescope
You’ll want to get your telescope set up early, in a place that has a clear view of the horizon. Remember that Mercury will be, at most, 12 degrees above the horizon. Keep your telescope aimed low and you should be able to get sight of the planet shortly after it rises.
Looking at Mercury through a telescope is the only way to see its phases. Consult your phone app to know what phase you can expect to find during your observation period. Planning to observe Mercury when the planet is as close to “full” as possible will help you find it more quickly.
You’ll want to be facing east if you’re observing Mercury in the morning and west if your observation is taking place at night. Remember that Mercury stays close to the sun, so aim your telescope at the very point where the sun will meet the horizon, and you should be able to find the planet with a little bit of determination and patience.
It may be helpful to try and spot Mercury through binoculars before zeroing in on it with your telescope. After that, center the planet in the crosshairs of your finderscope before looking through your telescope’s eyepiece.
Which telescope is best for observing Mercury?
You don’t need a particularly large telescope to be able to spot Mercury. A small telescope with a moderate level of magnification will work just fine. Use a telescope of at least 2.4″ (60 mm) aperture. Something like the Celestron FirstScope if you are on a budget.
A great telescope to use would have a 4″ (100 mm) aperture and tracking capabilities like the Celestron NexStar 4SE, to help you keep the planet in view for as long as possible.
Eyepieces, And Filters For Observing Mercury
Though you’ll be able to see Mercury just fine with a standard setup for your telescope, having special filters could help you to get an even better view. If you want to reduce the glare of the sun to clear up your view of Mercury. You should use an orange color filter. Use something with a Wratten Number like #21 Orange, and you’ll have an unimpeded look at the smallest planet in the solar system.
What does Mercury look like through a telescope?
Because of Mercury’s proximity to the sun, it will never be one hundred percent visible through your telescope. You will, however, be able to see Mercury during its first and last quarters. Mercury will look generally like our moon during those phases, but looking at Mercury through a telescope will reveal some surface features.
The planet may appear slightly pink unless you’re looking at it through a color filter. You will likely be able to see somewhat distinct shapes and features on the planet. Unfortunately, Mercury is too far away for you to resolve craters with a standard telescope.
Telescope views of Mercury
Through larger aperture telescopes, Mercury’s surface details can become much clearer. Mercury and Mars are the only terrestrial planets whose surfaces can be somewhat distinguished through a commercially available telescope.
Can You See Mercury Without a Telescope?
Because Mercury is so bright, it can be seen without a telescope. With some difficulty and practice, you can spot Mercury along the horizon with your naked eye. It’s even easier to see Mercury through a powerful set of binoculars. The Earth’s atmosphere will distort Mercury’s pinkish glow, but you can observe the shape of the planet through binoculars until the sun’s light blots it out.
There you have it, everything you need to know to see Mercury through a telescope or with your own eyes. Now it’s up to you to go out and practice.
The joy of finding one of our planets within the solar system should be on every astronomer’s to-do list. If you want to observe every planet through a telescope then we have a guide for everyone. For all the tips and tricks for getting the best views of Venus, Mars, Saturn, Jupiter, Uranus, Neptune then we have a guide for you.