Earth at perihelion on January 2, 2008
11 comments Print Me Email to FriendTonight's Sky for Wednesday, Jan 02 2008
Around sunset tonight, U.S. time, you will be as close to the sun as you will be for all of 2008. Earth will be at perihelion – from Greek words “peri” meaning near, and “helios” meaning sun.
What’s more, tomorrow morning the moon will be at apogee. Apo = farthest. Gee = Earth. The moon will be farthest from Earth tomorrow morning.
It’s just a coincidence that perihelion happens so close to the December solstice. Likewise, it’s a coincidence that the perihelion and the new year both occur around the same time. Some 10,000 years from now, perihelion will happen around the June solstice.
Next you are possibly asking yourself, “Why are those of us in the northern hemisphere cold now, if we closest to the sun?” The sun is now nearest for the year at 147 million kilometers (just over 91 million miles) away. But that relatively near sun doesn’t get high in the sky now, as seen from Earth’s northern hemisphere. Sunlight is striking this hemisphere more indirectly now than in summer. Plus, our northern hemisphere days – though lengthening now since the December solstice – are still relatively short.
Aphelion – the point at which the sun will be farthest from the sun for 2008 – will occur just after midnight on July 4. Earth will be farthest from the sun, but it will be hotter for us in the northern hemisphere because the sun – at 152 million kilometers (94 million miles) away – will be riding high in the sky and can beam those rays directly down on us for more hours and minutes.
The moon has a perigee (closest point) and apogee (farthest point) every month. That’s because the moon orbits Earth once each month in an orbit that is almost, but not quite, circular.
The points at which astronomical objects are the closest or farthest are also called apsis. And the moon does appear larger when it is at perigee … simply because it is closer.
Today’s image is from NASA, by the way. It was taken by Galileo probe. The four shots of the Earth were taken when Galileo was at perigee. In 2003, this spacecraft was so perijove that it crashed into Jupiter.
Shouldnt you way less right now because the sun has a greater gravitational effect on you? Also I read that as the hubble telescope goes around the Earth it goes through large temperature changes. My question is how does the telescope cool down in space. It heats up from radiation but you cant lose heat through convection in a vacuum. So how does Hubble lose all the heat from the sun?
No you won’t weigh less. Actually if you have more gravity then you weigh more. Or is it the holiday meals that cause us to weigh a little more this time of year?
As far as the cooling of the Hubble Space Telescope (HST), I was privileged to attend a press conference where the marker-size “air conditioners” were shown off during an update of the latest but hopefully not the last servicing mission. Sorry I’m not a space telescope engineer so hopefully this website can answer your questions: http://hubblesite.org/the_telescope/team_hubble/servicing_missions.php
Yeah there is more gravity. More gravity pulling you away from the Earth. The only way air conditioners could cool Hubble is if wires attached hubble conditioners allowing conduction of heat. Unless there is a gas inside hubble you cant cool something with convection which is the way airconditioners cool our houses.
@ Bob:
Yes, you will weigh less (at noon; at midnight you will weigh more)... by an insignificantly small amount. Although the Sun’s mass is about 300,000 times that of the Earth, it is also 30,000 times further away from you (distance between between centers of mass). This means that the force it has on you (average) is about .0003 times that of the Earth. Now, the difference between perihelion and aphelion is about 3 million miles, or about 3%. The change in force resulting from this is small, to say the least. These effects are all far outweighed by normal daily fluctuations in a person’s weight as they eat, drink, etc.
As for Hubble, it doesn’t have to lose heat by convection (it can’t anyway, as you pointed out). It loses heat by radiation, just as it absorbs it from the Sun. So Hubble’s cooling systems are not traditional air conditioners by any means. From the website Kelley posted, Hubble uses a skin of insulation to prevent heat from being efficiently conducted into the telescope, and it can radiate away all of this heat during its night (about 45 minutes to an hour IIRC).
Cari and Kelly are speaking about radiational cooling- the same way frost can form on objects (car windows, grass, rooftops) even though the ambient temperature is above the freezing point.
Carl is wrong. You’ll weigh less at both noon and midnight than at sunrise and sunset. Think of it as the Sun pulling you away from Earth at noon, and pulling Earth away from you at midnight. Of course, the Moon has a much greater effect, just as it does with the tides. Remember, we have two high tides a day because of this pull in both directions.
pretty nice
sure….
I like that
So basically the heat can go off hubble through waves? Ok makes sense thank you and uhh for Dak if what you are saying is true then basically you are saying that the Earth is held in place by your gravity which is not accurate.
What planets are in this east the a.m.?