Planetary Oddball Uranus Tempts Skywatchers On October Nights

Uranus is one of the two “ice giant” planets, edging out Neptune as the third largest planet. Its atmosphere is mostly hydrogen and helium with enough methane to tint the planet blue. Deep inside, Uranus has a rocky core surrounded by a thick rind or slushy ice. Uranus is “only” 1.77 billion miles from Earth this October. Credit: NASA/ESA/L. Sromovsky

This week, Thursday to be exact, the planet Uranus and Earth will be at their closest for the year. This special day is called opposition and refers to Uranus appearing opposite the sun in the sky. When the sun sets, the 7th planet will crest the eastern horizon, arc across the sky the entire night and then set at sunrise.

When planets are at opposition they’re not only closest but brightest. Bright of course is a relative term. Mars at opposition can become much brighter than Sirius, the brightest star. Uranus shines meekly at magnitude 5.7 slightly above the naked eye limit. On dark nights if you know exactly where to look, you can glimpse the planet without optical aid. I’ve seen it many times; my hope is that with the help of these maps, you will too.

Engraving of 18th century astronomer William Herschel in his element.

English astronomer John Flamsteed was the first to see Uranus in 1690 but thought it was just another star in the constellation Taurus. He even gave it a name: 34 Tauri. Despite running across it at least six times he never realized he was looking at a planet and not a star.

Enter William Herschel, a German transplant living in Bath, England and passionate sky watcher who never missed a clear night. From his garden on 19 New King Street, he stumbled across what he thought was a new comet in Taurus in his homemade 6-inch reflecting telescope on Tuesday night March 13, 1781. Closer examination of the object at high magnification showed it as a fuzzy disk, distinct from the point-like stars.

Extract from William Herschel’s journal entry made on March 13, 1781. The second paragraph reads: “In the quartile near Zeta Tauri the lowest of 2 is a curious either nebulous star or perhaps a Comet.” Source: Journal of the Royal Astronomical Society

Like any good comet hunter then or now, Herschel returned to his “comet” several nights later on the 17th to see if it had moved. For all practical purposes stars are fixed, but planets and comets inch across the sky as they orbit the sun. They can’t help but give themselves away.

Herschel next reported his find to England’s Royal Astronomical Society so others could see and track the new object. Very soon, astronomers realized this was no comet but a brand new planet, the first discovered since antiquity.

Because its axis is tipped 98 degrees, Uranus orbits the sun spinning on its side. The poles alternately face the sun for 42 years at a time. Credit: Nature of the Universe

And what an odd planet! We now know that Uranus is not only the coldest planet in the solar system – even chillier than more distant Neptune – but the only one that spins on its side. Like Earth, most of the planets spin like tops with their rotation axes tilted a little this way or that, but Uranus takes it to the extreme with a tip of 98 degrees. Seen from afar, it looks like a ball rolling on its side, and that has some curious consequences when it comes to seasons.

Since Uranus takes 84 years to make one spin around the sun, each of the planet’s poles gets 42 years of continuous sunlight during the summer season followed by 42 years of winter darkness. The northern hemisphere currently faces the sun with the first day of Uranian summer due in 2028.

Because of the planet’s extreme axial tilt, we see Uranus from different perspectives over its 84-year orbit. Right now the view is “opening up” again after a near “edge-on” view in 2006. Credit: NASA/ESA/G. Bacon – STScI

“Day” is something of a misnomer. A day on the planet lasts a little more than 17 hours, but as seen from the poles, a day in the traditional sense lasts 42 years. If you could hang out at one of the poles, the sun would rise on the first day of spring, creep slowly across the sky and finally set on the first day of fall 42 years later.

Uranus comes up into view around 9:30 p.m. local time in the southeastern sky below the Great Square of Pegasus and to the right of the small constellation Aries. It’s not far from the star Delta in Pisces. Once you find Delta with eye and binoculars, you’re ready to use the detailed map below. All maps: Stellarium

Uranus is the third largest planet, edging out distant Neptune by just 85 miles. All the large outer solar system planets radiate heat from their cores which are still contracting under the force of gravity since their formation 4.5 billion years ago. Contraction creates heat which escapes the core and spills into space.

Delta heads up a little row of stars that points toward the planet Uranus. If you place Delta to one side of your binocular view, you’ll see Uranus near the other side. The planet is the same brightness as the 5.7 mag. star. Positions are shown every 5 days from Sept. 30 to Oct. 15.

Oddball Uranus gives off little internal heat and no one’s sure why. Temperatures as low as -371 degrees F (-224 C) have been recorded in its lower atmospheric layers. Scientists hypothesize that there might be some sort of barrier deep below the atmosphere that blocks heat coming from the core. That or the planet was struck by another developing planet long ago, causing it to expel its internal heat as well as knocking the axis kittywampus.

Uranus and a few of its moons as seen in the Hubble Space Telescope. The planets also has at least 13 very narrow rings composed of water ice coated by dark, organic materials. Credit: NASA/ESA

While Uranus may be challenging to see with the naked eye, it’s easily visible in binoculars even in less than ideal skies. That’s the good news. The bad news is that the planet isn’t near any bright stars that would give a beginning observer a leg up in finding it. No problem. We’ll get you there anyway.

Through a telescope magnifying about 75x you can tell you’re looking at a planet and not a star. Stars are tiny and possess a fiery radiance; Uranus looks slightly larger and “dull” in comparison. Once you crank up the power to 150x and higher, you can’t miss its tiny disk, tinted blue from atmospheric methane gas. Amateur astronomers using scopes in the 12-inch to 16-inch range can even spot two of the planets 27 known moons, Titania and Oberon.

Uranus moves slowly westward through the constellation Pisces during October. You can watch its progress in binoculars as it passes among several “fixed stars” of similar brightness. Face southeast starting around 9:30 – 10 p.m. when the planet has cleared the trees and houses and begin by locating the Great Square of Pegasus, a big, vacant square of sky with a star marking each of the four corners. Drop down one outstretched fist below the Square to find the dimmer star called Delta in the constellation Pisces. Now center your binoculars on Delta and use the map below to hone in on the planet’s location.

I wish you well in discovering the 7th planet all by yourself just as Herschel once did.

26 Responses

    1. astrobob

      More fearmongering. Repent, repent, repent. That’s a video of the asteroid Vesta assembled from still images taken by the Hubble Space Telescope.

    1. astrobob

      Yep, Galileo was the first to see Neptune as was Flamsteed the first to see Uranus. Neither one followed up.

  1. randy

    You mentioned that its northern hemisphere is facing the sun. How is north defined when a planet spins on its side? Or for any planet, actually, since there is no up or down in space?

      1. RC

        Just to add some clarity (correct me if I’m wrong) – The sun always rises in the east on a planet. This means that the planet rotates counter-clockwise about its north pole, and clockwise about its south pole (when looking from above).

        1. astrobob

          Yes, for most planets in the solar system. Venus however rotates in reverse (retrograde), so the sun rises in the west and sets in the east. Not that anyone on the planet’s surface would see it of course! Technically, Uranus and Pluto (once considered a planet) also rotate in retrograde since their axes are tilted 98 degrees and 120 degrees respectively. Anything past 90 degrees puts a planet’s spin counter to the norm for the solar system. What likely caused these odd tilts are impacts by large objects.

          1. Bob Crozier

            Hey Bob,
            How can this be? How large of an object would it take to stop an entire planet from spinning (I can’t even imagine how much momentum there is in a spinning planet!), and then, *more than that*, to make it actually spin the other way? Wouldn’t such a collision just completely destroy both objects? And, if that is what happened, where are those objects or their remains now? For example, is there any remaining evidence either on or around Venus now of such a collision?

          2. astrobob

            Let’s take a look at Earth and moon. The prevailing theory of the moon’s origin is a glancing blow from a Mars-sized planet with Earth. Material from the collision eventually formed the moon and without a doubt would have affected both Earth’s rotation and axial tilt, yet didn’t completely destroy the planet. The collision with Venus – assuming that’s what caused the slow rotation (there are competing theories) – would have happened so long ago that whatever evidence there was has moved on, perhaps re-absorbed into the planet. I’ve not heard of any physical evidence for a Venus-developing planet collision.

          3. RC

            Thanks for clearing that up for me. That “rule” was something I had read once on the internet, but I never put full faith into it. Proof yet again that the phrase “you can’t believe everything you read on the internet” holds true!

  2. Robert

    Hi Bob- well my question was similar to Randy’s in that there is no real up or down in space. I didn’t know that up and down was based solely on what we earthlings perceive as up or down. It would be funny if by some devine intervention we found out that we have been looking at everything up side down. Just a funny thought

    1. astrobob

      Yes, these are fun things to think about. There is no direction in space unless defined by where you want to go or where you’re coming from. Funny to think about our “silly” conventions of north and south extended into the cosmos. Another interesting thing to consider is the galaxy itself which has a galactic equator and north and south poles. Since the plane of the galaxy is tilted 60 degrees with the respect to the plane of Earth’s orbit, north and south poles on Earth depart significantly from galactic north and south poles.

  3. Troy

    That top image has what must be a rarity of rarities; a Uranus eclipse. Pretty sweet I haven’t seen that one before. I envy your dark Duluth skies, I can’t imagine seeing it with the naked eye. I’ve tried observing (and photographing) Titania and Oberon in my 8″SC to no avail. I was hoping opposition might pull them in better but judging by your article I rather doubt I’ll see them.

    1. astrobob

      They are faint – around 14th magnitude and visible very faintly in my 15-inch scope when seen at elongation. Are you using a CCD camera? If so, try photographing them when they reach max. elongation from the planet and furthest from its glare.

  4. Troy

    My camera is a NexImage5. It is possible to take up to 30s exposures but even 2s exposures produce a lot of artifacts as a side effect. Sometimes they can be removed by merging them with a dark frame but I need to see what’s going on as it happens. According to S&T Oberon and Titania have been seen in an 8″ but my observing site isn’t optimum so I’ve pretty much given up, especially if they are faint in a 15″. (It is odd I thought I had successfully photographed Titania but it seemed in the wrong place, though Stellarium didn’t show any star there.)

      1. Troy

        I have tried stacking. Uranus comes out very nice but I haven’t confirmed any moons yet. I’m going to try again this week, instead of using castrator to decrease the image size I’m going to try to set up a region of interest during imaging.

        1. astrobob

          I think all you need now is to know when each or both are at max elongation. I can’t find an online program but I can find out with SkyMap software. Do you have software that will show the positions of the moons. I’m not sure about Stellarium but I know SkyMap is accurate.

  5. caralex

    Bob, how would a collision topple a gas planet, like Uranus? I’m trying to imagine how this could happen with such a huge envelope of gas surrounding it!

    1. astrobob

      Good question. Hard to imagine but I suspect if a collision occurred it happened between the icy / rocky core and another object.

  6. Sean

    This is only my 2nd year of tracking Uranus and Neptune or at least the region where Neptune is located since it’s ?able how many times i’ve actually seen it. But i find myself 1st navigating to where the planets were last year and then tracking my binos a little further east. i find this easiest, sort of like following a familiar road b4 turning onto a less-known one. so for Uranus i start near the circlet of Pisces, then track S and i think E a little to this parallelogram of 4 stars, the top 2 of which “point” E toward a group of 6 stars (3 of which are somewhat brighter and form sort of a triangle, one star on the bottom) near which Uranus was last year, the i go E till Uranus which is right near another star right now but i always continue to extremely recognizable delta with its companion, just to make absolutely sure i’m in the right place. i suppose i could save time by just finding delta 1st. similarly with neptune, i go from the water jar S to theta, with 2 other stars forming a triangle, then S to the star it was near last year then E to its current location, and the brighter recognizable star nearby being sigma i think? anyway, Neptune is a real challenge from my somewhat light-polluted skies.

    1. astrobob

      Yours is a good way to find the planet. Like you I’ve found that if I follow Uranus and Neptune for a little while I soon memorize the stars they’re now and find it easy to spot them any old night.

Comments are closed.