Portal:Astronomy/Help desk

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This is the place to ask questions about astronomy. You can also request an astronomy topic that you would like to learn here at Wikiversity.

The Moon[edit]

What is the phase of the moon today?

Information about the current phase of the moon can be found at the US Naval Observatory webpage: What the Moon Looks Like Today--mikeu 10:29, 16 December 2006 (UTC)

The moon looked like almost a half moon for one part of the moon was shaded dark what kind of moon is it? Let me know of this Mike ;-) belia


Phases of the Moon.png

Here are the names of the phases of the moon. You can click here to see a larger image. The next time you see the moon in the sky take a look at this image and pick the one that most looks like what you saw in the sky. Today (Dec. 13, 2007) the moon is a crescent. It takes about one month for the moon to change through all the phases. The dark shaded part is where it is night time on the Moon.--mikeu 22:46, 13 December 2007 (UTC)

The Earth and Moon

This image shows what the Earth and Moon look like from space. Click on the image to see a larger view. The picture was taken by a spacecraft exploring Mars. Notice that both the Earth and Moon are First Quarter. The Sun is shining from the right and lighting up just the right half of both the Earth and Moon.--mikeu 13:32, 18 December 2007 (UTC)

Mars[edit]

Hi mu301, thank you for I can be bold. Mars es getting closer to us.

Yes, Mars is very close to the Earth right now (late Dec. 2007 - early Jan. 2008). Astronomers use this opportunity to study Mars, because it allows us to see details on the planet that are usually very difficult to see. When the planet is close to the Earth it looks larger in the telescope. The last time Mars was this close was Nov. 7, 2005 and the next chance to see such a good view of Mars will be Jan. 29, 2010. So what can we see on Mars? Take a look at the picture. The very bright white at the bottom edge is the polar ice cap. The slightly blueish white to the bottom left and at top are clouds. The redish orange parts of the planets are deserts covered with sand and dust. The dark spots are rocky places.
I hope that pun was intended... 217.255.172.55 (discuss) 11:13, 11 April 2014 (UTC)

Cluster of seven galaxies by Orion's belt.[edit]

10 or 15 years ago my brother pointed out to me a fuzzy spot just the right of Orion's belt. Through his 16 power binoculars it was easy to see the spot was really a cluster of seven spiral galaxies. He called them the Seven Sisters. I know that is incorrect but does anyone know what they are really called, if they have a name?

Richard Epling

The "Seven Sisters" are the W:Pleiades (which are actually stars in Taurus, not galaxies in Orion). Perhaps what you were seeing was the W:Orion Nebula, also known as M42 ? There are several such objects in Orion, containing protoplanetary disks, which can easily be confused with spiral galaxies. The location doesn't seem quite right for M42, however, as that's under the belt, not to the right. Can you tell me which object on the map you meant (is it the one labeled "η") ?
Click on to see large image
StuRat 21:50, 9 June 2008 (UTC)

On Autumnal Equinox the Sun is setting. The Moon is rising at this moment. What is the RA of the Moon?[edit]

On Autumnal Equinox the Sun is setting. The Moon is rising at this moment. What is the RA of the Moon? —The preceding unsigned comment was added by 72.203.146.27 (talkcontribs) 22:20, 10 September 2008 (UTC)

At the moment of the autumnal equinox the Sun would be at RA = 12 hours, by definition. If the Sun is setting at the same time that the Moon is rising, this would mean that the Moon is full. The Moon would then be at an RA of about 0 hours. (It could be slightly off from exactly 0 hours due to the orbit of the moon being inclined to the ecliptic.)
A full Moon on the day of the equinox is not that common. But it does happen on Sept. 23, 2010. For Greenwich, England the Moon rises at 17:27 UTC and is at RA = 00h 09m 36.29s and the Sun sets at 17:57 UTC and is at RA = 12h 01m 39.74s. The exact moment of the equinox is 3:09 UTC and the exact moment of full Moon is at 9:17 UTC. --mikeu talk 00:26, 8 February 2009 (UTC)

Solar fusion[edit]

If the nuclear fusion reaction of converting 4 H ! He occurs at an efficiency of 0.7%, and that mass is converted into energy according to the equation E = mc2, then estimate the Main Sequence lifetime of the Sun (spectral type G2) in years if the luminosity of the Sun is 3.83×1033 ergs s−1. Assume the Sun’s core (10% of the total mass) is converted from H into He. The Sun’s mass is M⊙ = 1.9891 × 1033 g. {unsigned2|15:33, 5 November 2008|147.226.200.244}}

I can help with the nuclear fusion part, but not the astronomy part of the problem. First you need to look up the atomic masses of hydrogen and helium. Assuming the most common isotopes of each, we get an isotope mass of 1.00782503207 u for hydrogen-1 and 4.00260325415 u for helium-4. Now let's do some math for 4H1 → He4:
 (1.00782503207 u × 4) - 4.00260325415 u = 0.02869687413 u
So, that's the mass to plug into E = mc2. Hopefully someone else can help you from there on. StuRat 21:16, 6 November 2008 (UTC)

galactic alignment[edit]

the question below was copied from Category talk:Astronomy --mikeu talk 18:59, 7 February 2009 (UTC)

The planets will align soon so what will be and don't give any sarcastic remarks please really tired of it just scientific remarks is all and not negative ones.—The preceding unsigned comment was added by 71.235.27.226 (talkcontribs) 20:46, 30 January 2009 (UTC)

This gets a little complicated to explain, so I'll give a short answer now and add more later. In particular, I'll see if I can find (or create) a map of the sky that illustrates this.
There has been a lot of speculation about an alignment that is supposed to be related to the Mayan calendar. (See for example: 2012 and the Long Count, 2012 geophysical and cosmological speculations and 2012 metaphysical speculations.)
But your question is about the alignment, so I'll just focus on that. There is a page on wikipedia that describes the scientific alignment at w:Galactic Alignment. Unfortunately, that page is not very well written. I'll see if I can improve the information there. The alignment is between the point in the sky where the sun would be on the day of the winter solstice and the equator of our Milky Way galaxy. The exact aligment already occured in May of 1998. --mikeu talk 19:36, 7 February 2009 (UTC)
As for what will happen to the Earth at that time, the answer is "nothing unusual". The third external link at our article covers that pretty well: [1]. StuRat 22:07, 7 February 2009 (UTC)

Really? the last alignment happen on 1998. I'm confused, the alignment happens every 26,000 years. Christian Louie M. Pajaron

Since the Sun is not a point, but has a large diameter when viewed from the Earth, it takes 36 years to pass through the plane of the ecliptic. This started in 1980 and will end in 2016. So, the center of the Sun passes the ecliptic in 1998. 2012 is during this period, but that year isn't very "special", being neither the year when the process starts, is halfway complete, or ends. Thus, it looks very much like it's just a coincidence that the Mayan calendar ends on that date, or, if it's not a coincidence, the Mayan math was apparently off a bit. StuRat 15:35, 9 December 2009 (UTC)
I'd be surprised if we had measurements exact enough to determine this to any precision. The period of this alignment is about 33 million years, not 26000 years. 26000 years is the period of w:Axial precession (astronomy), i.e. the time it takes the Earth axis to perform one "wobble". --Stephan Schulz 14:01, 6 April 2010 (UTC)

I think the Mayans use spirituality and a bit mathematics to make their calendar and you're right, it's really weird coincidence that their calendar ends on 2012. Christian Louie M. Pajaron 12:29 Philippines February 3, 2010

It does not. What ends is one of several cycles of the Mayan calender, just like midnight does not end our calender, but only one 24 hour cycle. --Stephan Schulz 13:54, 6 April 2010 (UTC)
Well, the day ends at midnight, then a new one begins. Similarly the Mayan calendar ends in 2012, then a new one begins, just like our yearly calenders end in December 31st, then a new one begins. This is using definition 2 at Wiktionary:calendar, while you are using def 1. StuRat 14:22, 6 April 2010 (UTC)

Exponential expansion of the Universe[edit]

My studies have led me to the conclusion that the Big Bang is the result of gravity being a polar force, the opposite pole of which I call anti-gravity. This anti-gravity force is also the cause of the exponential expansion of the universe and explanation why the universe is expanding exponentially in the presence of less gravity to slow it. However, I think this is original research and can not add it to an article in the Wikipedia and so after asking the question if this is original research or if others have reached the same conclusion I was referred hear on the idea that the Wikiversity has not ban on OR. What article here then might I add my conclusion to in a sentence or paragraph? 71.100.11.118 20:56, 3 March 2010 (UTC)

How has the Sun benefited astronomy?[edit]

?

The most obvious way is that there would be no life on Earth, and hence no astronomy or astronomers, without the Sun. The next most obvious way is that it helped Kepler work out orbital dynamics and Newton figure out how gravity affects the planets and moons. More recently, it's been used to study sunspots, stellar rotation, solar magnetic fields, the solar corona and internal structure, etc. StuRat 12:51, 30 April 2010 (UTC)

Expanding Universe?[edit]

Some say the Pulsating Theory is true, which means the universe has no beginning and no ending and the universe continues to expand wider and wider throughout time. Is it true or plausible? —The preceding unsigned comment was added by 112.198.233.141 (talkcontribs) 08:41, 19 July 2010 (UTC)