# Solstices, Perihelion and Aphelion **URL:** \ **Category:** Factual Questions\ **Created:** [December 21, 2020, 4:21pm UTC](https://boards.straightdope.com/t/solstices-perihelion-and-aphelion/928547 "2020-12-21T16:21:12Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![Jim\_B](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jim_b/32/4338_2.png) [@Jim\_B](https://boards.straightdope.com/u/Jim_B)\ **Post date:** [December 21, 2020, 4:21pm UTC](https://boards.straightdope.com/t/solstices-perihelion-and-aphelion/928547/1 "2020-12-21T16:21:12Z")
Yes, my confusion and question is what are the solstices. But what really confuses me is how do they relate to the Sun’s perihelion and aphelion? Perihelion is when the Sun is furthest from the earth. Aphelion is when it’s closest. The aphelion occurs in January I think. That actually makes sense. Because January is the coldest month, at least in North America. And surely it is no accident some celestial event coincides with it. (As to why the earth is _closest_ when it’s _coldest_, in first grade they told us it has to do with how the Sun’s ray’s focus on it or something. Enough said about that, for now at least 🙂 .) I at least can understand a simple concept like that. Closest/farthest. So then what’s the big deal about the Solstices? And how specifically do they relate to the weather? Also solstice literally means when the sun stands still. What on earth does that mean? Thank you in advance for your civil replies 🙂 . People who merely want to criticize my question need not post. Thank you. 🙂 ---
**Author:** ![Great\_Antibob](https://avatars.discourse-cdn.com/v4/letter/g/e47c2d/32.png) [@Great\_Antibob](https://boards.straightdope.com/u/Great_Antibob)\ **Post date:** [December 21, 2020, 4:45pm UTC](https://boards.straightdope.com/t/solstices-perihelion-and-aphelion/928547/2 "2020-12-21T16:45:29Z")
Lots of questions here. The solstices are when the sun will appear to be the furthest north/south it will ever get that year (when the sun “stands still” in its north/south migration. This effect is more noticeable the further north or south you get. So, in NYC or London or something, even at noon in winter, you cast long shadows, because the sun never appears to be directly overhead during the day but off to the north at all times. Why we see this effect is due to earth’s axial tilt. We revolve around the sun on a plane (think record on a turn table) but the earth’s axis is tilted from this flat level by ~23 deg. As for the relationship to weather, that also has to do with earth’s axial tilt more than proximity to the sun, which is related to the solstices but less so perihelion/aphelion. Due to earth’s tilt (~23 deg), during the season’s we’re tilted away from the sun (right now for the Northern hemisphere), we get less sunlight each day and it’s cooler on average. When we’re tilted toward the sun (right now for the Southern hemisphere), we get more sunlight each day and it’s warmer on average. The tropics (+/- ~23 deg latitude) always get about the same amount of sunlight every day and there’s less (or no) seasonal variation. Perihelion and aphelion are not directly related to the solstices. At the moment, earth is closest to the sun about 2 weeks after the December solstice, but they drift. If you are willing to wait several thousand years, you’ll be able to witness years where they occur at the equinoxes or when we’re closest to the sun during the Northern Hemiphere’s summer. ---
**Author:** ![FrenchDunadan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/frenchdunadan/32/5449_2.png) [@FrenchDunadan](https://boards.straightdope.com/u/FrenchDunadan)\ **Post date:** [December 21, 2020, 5:20pm UTC](https://boards.straightdope.com/t/solstices-perihelion-and-aphelion/928547/3 "2020-12-21T17:20:21Z")
And the shorter or longer distance is not very significant. in January 0,983 UA in July 1,017 UA so 1,7% of variation in distance ( and ± 100w/m² of the 1 360 w/m² that we receive) Summer in the south hemisphere are a little hotter than in the north cause of that small energy. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [December 21, 2020, 5:22pm UTC](https://boards.straightdope.com/t/solstices-perihelion-and-aphelion/928547/4 "2020-12-21T17:22:38Z")
> [@Jim\_B](#): > > Perihelion is when the Sun is furthest from the earth. Aphelion is when it’s closest. The aphelion occurs in January I think. That actually makes sense. Because January is the coldest month, at least in North America. And surely it is no accident some celestial event coincides with it. (As to why the earth is _closest_ when it’s _coldest_ , in first grade they told us it has to do with how the Sun’s ray’s focus on it or something. Enough said about that, for now at least 🙂 .) Your first grade teacher should have said even less, perhaps… Distance from the sun is not the cause of seasonal temperature variation. As @Great_Antibob has said, the seasonal variation in energy input from the sun (insolation) is due to variation in the _angle_ of incidence of the sun’s rays - how high or low it is in the sky - because the earth’s axis of rotation is tilted relative the plane of orbit. [https://www.nationalgeographic.org/media/seasons-wbt/](https://www.nationalgeographic.org/media/seasons-wbt/) Minimum insolation occurs at the winter solstice. The fact that coldest temperatures occur much later is called **seasonal lag** , and it’s because of the large amount of energy held in water. The oceans take a long time to cool down and warm up. > **[Seasonal lag](https://en.wikipedia.org/wiki/Seasonal_lag)** > > Seasonal lag is the phenomenon whereby the date of maximum average air temperature at a geographical location on a planet is delayed until some time after the date of maximum insolation (i.e. the summer solstice). This also applies to the minimum temperature being delayed until some time after the date of minimum insolation. Cultural seasons are often aligned with annual temperature cycles, especially in the agrarian context. Peak agricultural growth often depends on both insolation levels and so... ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [December 21, 2020, 6:05pm UTC](https://boards.straightdope.com/t/solstices-perihelion-and-aphelion/928547/5 "2020-12-21T18:05:21Z")
> [@Jim\_B](#): > > Perihelion is when the Sun is furthest from the earth. Aphelion is when it’s closest. The aphelion occurs in January I think. Nitpick: you have the definitions backwards. Perihelion is the point in the orbit when a planet is closest to the Sun; aphelion is farthest. For Earth, aphelion is in early July; perihelion is in early January. ---
**Author:** ![k9bfriender](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k9bfriender/32/3283_2.png) [@k9bfriender](https://boards.straightdope.com/u/k9bfriender)\ **Post date:** [December 21, 2020, 6:19pm UTC](https://boards.straightdope.com/t/solstices-perihelion-and-aphelion/928547/6 "2020-12-21T18:19:19Z")
If nothing else, think of it this way. If seasons were caused due to the distance from the Earth to the Sun, then the whole Earth would always be in the same season. As the Southern hemisphere is in Winter when the Northern is in Summer, and vice versa, this demonstrates that the distance has very little to do with the seasons. ---
**Author:** ![AHunter3](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ahunter3/32/368_2.png) [@AHunter3](https://boards.straightdope.com/u/AHunter3)\ **Post date:** [December 21, 2020, 6:27pm UTC](https://boards.straightdope.com/t/solstices-perihelion-and-aphelion/928547/7 "2020-12-21T18:27:40Z")
> [@Jim\_B](#): > > Yes, my confusion and question is what are the solstices. But what really confuses me is how do they relate to the Sun’s perihelion and aphelion? Completely and utterly unrelated. Perihelion and aphelion are only accidentally kind of close to the solstices. They could just as easily be right next to the equinoxes instead. On our planet, perihelion and aphelion have very little effect on the weather. On some other hypothetical planet whose orbit was far more elliptical, that might not be the case. In earth’s southern hemisphere, the coldest months are during the time of year when the earth is farthest away from the sun. But that’s accidental and irrelevant. At that exact same time of year, the northern hemisphere is having its warmest months. The solstices are the points of maximum effect of the tilt of the axis — either fully towards or fully away from the sun. The part of the planet tilted away keeps losing heat day by day until it gets downright cold — it radiates away the heat during the long night and doesn’t absorb enough to make up for it during the short day. The other part of the planet, tilted towards the sun, is doing the opposite, absorbing more heat during the long days than it can get rid of during the short nights. Right now, South Africa and Patagonia and Australia and New Zealand are getting baked, while Europe, Asia, and North America are shivering. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [December 21, 2020, 7:12pm UTC](https://boards.straightdope.com/t/solstices-perihelion-and-aphelion/928547/8 "2020-12-21T19:12:08Z")
Right now, at the (northern) winter solstice, the sun rises late and sets early, and even at noon, it’s not very high in the sky. All of that is because of the solstice, and it’s directly related to why it’s cold (and getting colder) right now. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [December 21, 2020, 8:30pm UTC](https://boards.straightdope.com/t/solstices-perihelion-and-aphelion/928547/9 "2020-12-21T20:30:11Z")
> [@Jim\_B](#): > > … > Perihelion is when the Sun is furthest from the earth. Aphelion is when it’s closest. > … Somebody else already addressed the mix-up about closest vs farthest. I’ll point out the emphasis and implied causation is backwards too. It’s not that the Sun is closest or farthest from Earth. It’s that the Earth is closest or farthest from the Sun. At any moment the numerical distance is the same measured in either direction. But the _why_ of the various distances over time is all about Earth moving and the Sun being all-but stationary in relation. There’s quite a good article here with a nice diagram of the various points around the orbit: > **[Earth's orbit](https://en.wikipedia.org/wiki/Earth%27s_orbit)** > > Earth orbits the Sun at an average distance of 149.60 million km (8.317 light minutes, 92.96 million mi) in a counterclockwise direction as viewed from above the Northern Hemisphere. One complete orbit takes 365.256 days (1 sidereal year), during which time Earth has traveled 940 million km (584 million mi). Ignoring the influence of other Solar System bodies, Earth's orbit, also known as Earth's revolution, is an ellipse with the Earth-Sun barycenter as one focus with a current eccentricit As ... The point I’ll make is that the geometry of the perihelion / aphelion line and the solstice line (or equivalently the equinox line) are constantly slowly shifting versus the fixed distant stars. And they shift at different rates. Right now Winter Solstice is within about 2 weeks of perihelion. In a few thousand years the equinox will be near perihelion. You can read more about how these things evolve over time here: [https://en.wikipedia.org/wiki/Milankovitch\_cycles#Earth’s\_movements](https://en.wikipedia.org/wiki/Milankovitch_cycles#Earth's_movements) ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [December 21, 2020, 9:20pm UTC](https://boards.straightdope.com/t/solstices-perihelion-and-aphelion/928547/10 "2020-12-21T21:20:32Z")
> [@LSLGuy](#): > > The point I’ll make is that the geometry of the perihelion / aphelion line and the solstice line (or equivalently the equinox line) are constantly slowly shifting versus the fixed distant stars. And they shift at different rates. Which also means that there are at least three different definitions of “length of the year”, with slightly different values. What we humans mostly use is the tropical year, the time from solstice one year to solstice the next, because that’s what matters for the seasons. But you could also use the apsodal year, from perihelion one year to perihelion the next, or the sidereal year, based on our position relative to the distant stars. I’ve heard speculation that one cause for the fall of the great Egyptian empires was the basis of their calendars: The heliacal rising of Sirius (that is, the day in the fall when you can just barely see Sirius, without it being lost in the glare of dusk) was a sign that the Nile would imminently flood, which was of critical importance in agriculture. But the heliacal rising of Sirius happens on a schedule based on the sidereal year, while the flooding is based on the tropical year, so they gradually got out of synch, and they lost the ability to accurately predict the floods. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [December 21, 2020, 9:30pm UTC](https://boards.straightdope.com/t/solstices-perihelion-and-aphelion/928547/11 "2020-12-21T21:30:24Z")
There’s a thorough discussion of Earth’s perihelion and aphelion here. > **[Apsis | Earth perihelion and aphelion](https://en.wikipedia.org/wiki/Apsis#Earth_perihelion_and_aphelion)** > > Currently, the Earth reaches perihelion in early January, approximately 14 days after the December solstice. At perihelion, the Earth's center is about 0.98329 astronomical units (AU) or 147,098,070 km (91,402,500 mi) from the Sun's center. In contrast, the Earth reaches aphelion currently in early July, approximately 14 days after the June solstice. The aphelion distance between the Earth's and Sun's centers is currently about 1.01671 AU or 152,097,700 km (94,509,100 mi). > The dates of perihelio... Some notable parts: > The dates of perihelion and aphelion change over time due to precession and other orbital factors, which follow cyclical patterns known as [Milankovitch cycles](https://en.wikipedia.org/wiki/Milankovitch_cycles). In the short term, such dates can vary up to 2 days from one year to another.[[14]](https://en.wikipedia.org/wiki/Apsis#cite_note-14) This significant variation is due to the presence of the Moon: while the Earth–Moon [barycenter](https://en.wikipedia.org/wiki/Barycenter) is moving on a stable orbit around the Sun, the position of the Earth’s center which is on average about 4,700 kilometres (2,900 mi) from the barycenter, could be shifted in any direction from it… > Perihelion and aphelion… have an indirect effect on the seasons: because Earth’s [orbital speed](https://en.wikipedia.org/wiki/Orbital_speed) is minimum at aphelion and maximum at perihelion, the planet takes longer to orbit from June solstice to September equinox than it does from December solstice to March equinox. Therefore, summer in the northern hemisphere lasts slightly longer (93 days) than summer in the southern hemisphere (89 days).[ > On a very long time scale, the dates of the perihelion and of the aphelion progress through the seasons, and they make one complete cycle in 22,000 to 26,000 years. ---
**Author:** ![SmartAleq](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/smartaleq/32/163_2.png) [@SmartAleq](https://boards.straightdope.com/u/SmartAleq)\ **Post date:** [December 22, 2020, 1:25am UTC](https://boards.straightdope.com/t/solstices-perihelion-and-aphelion/928547/12 "2020-12-22T01:25:23Z")
> [@Great\_Antibob](#): > > So, in NYC or London or something, even at noon in winter, you cast long shadows, because the sun never appears to be directly overhead during the day but off to the north at all times. Since we’re picking nits here, when you live far to the north, in winter the sun appears to always be in the SOUTH. In summer it swings up to the middle of the sky. At no time is the sun appearing to be in the northern part of the sky. Source: I live north of the 45th Parallel. I think it would discombobulate me to have the sun in the northern sky. ---
**Author:** ![Great\_Antibob](https://avatars.discourse-cdn.com/v4/letter/g/e47c2d/32.png) [@Great\_Antibob](https://boards.straightdope.com/u/Great_Antibob)\ **Post date:** [December 22, 2020, 1:32am UTC](https://boards.straightdope.com/t/solstices-perihelion-and-aphelion/928547/13 "2020-12-22T01:32:13Z")
> [@SmartAleq](#): > > Since we’re picking nits here, when you live far to the north, in winter the sun appears to always be in the SOUTH. Good catch! ---
**Author:** ![SmartAleq](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/smartaleq/32/163_2.png) [@SmartAleq](https://boards.straightdope.com/u/SmartAleq)\ **Post date:** [December 22, 2020, 1:40am UTC](https://boards.straightdope.com/t/solstices-perihelion-and-aphelion/928547/14 "2020-12-22T01:40:34Z")
Trust me, I literally get my nose rubbed in it every damned day of winter! That short weaky sunlight is actually harder to cope with than the endless rain, fog, clouds and gloom. Ah, the PNW! ---
**Author:** ![DemonTree](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/demontree/32/8646_2.png) [@DemonTree](https://boards.straightdope.com/u/DemonTree)\ **Post date:** [December 22, 2020, 1:53pm UTC](https://boards.straightdope.com/t/solstices-perihelion-and-aphelion/928547/15 "2020-12-22T13:53:47Z")
> [@SmartAleq](#): > > Since we’re picking nits here, when you live far to the north, in winter the sun appears to always be in the SOUTH. In summer it swings up to the middle of the sky. At no time is the sun appearing to be in the northern part of the sky. Source: I live north of the 45th Parallel. I think it would discombobulate me to have the sun in the northern sky. In summer the sun rises in the north-east and sets in the north-west in the northern hemisphere. And if you’re inside the Arctic circle it will be low in the northern sky at midnight. When I visited the southern hemisphere I didn’t really notice that the sun was in the north at noon, but it was weird having shadows move anti-clockwise through the day. ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [December 22, 2020, 2:07pm UTC](https://boards.straightdope.com/t/solstices-perihelion-and-aphelion/928547/16 "2020-12-22T14:07:47Z")
As for why it’s coldest in January, here’s an analogy. Imagine you are in a very badly insulated space (that’s like being in the temperate zone in either hemisphere) and you have an adjustable heater (which is like the Sun, due to the axial tilt). You keep turning the heater down and it gets colder and colder, because the heater delivers less energy than what is escaping through the walls. Then you stop turning it down (the solstice) and start turning it up. For a while it will keep getting colder, because the heater still isn’t delivering as much energy as what is escaping through the walls. It only stops getting colder when you pass the point where the heater is delivering as much energy as what is escaping. For actual weather this is of course complicated by energy moving around in the atmosphere. But the “coldest part of winter” is, averaged over time and space, still explainable this way.