Questions tagged [astronomy]

The study or observation of objects or phenomena outside the Earth, including the Sun, Moon, planets, and stars.

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Measuring Moon's elevation in units of length

Rosh Hashanah 24a: The Sages taught in a baraita: If one witness says that he saw the moon two plow handles high above the horizon, and the other one says it was three plow handles high, their ...
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Why does plant life come after the earth, waters and the firmament, but before the planets?

This question only addresses the blueprint of the creation as described in the first chapter of Bereshit. It does not address the sequence of the actual creation, as described in Bereshit 2, or the ...
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Sukkos 2a ~ Reality shows the need for 13-אמות while the Gemara states that the smallest Sukkah is enough?

ר׳ זירא says that a Sukkah that is lower than 20-אמות, the סכך is the one blocking the sun and creating the shadow, not the walls, and therefore the Sukkah is kosher, like it says in the פסוק ״וסוכה ...
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Meaning of Monen in Kabbalah

I came across the term "monen" but have been unable to find much information on it in scholarly or scriptural sources. The main information online appears to be a kabbalah-related stub on ...
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What is the relation between the month Nisan and the spring equinox?

I'm searching for the relation between Nisan and the spring equinox according to Scripture. I know of the texts Genesis 1:14, Exodus 12:2-3, Leviticus 23:15 and Deuteronomy 16:1. I find multiple ...
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A beracha on the "Great conjunction"?

Tonight (or earlier tonight in Israel) the planets Jupiter and Saturn come so close that one might think that they are a single star. Is this occasion to say the beracha of עושה מעשה בראשית? It is not ...
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How to observe Shabbat on Mars

Inspired by this question. The Martian day is 24 hours, 37 minutes long. After approximately 39 Martian days, 40 days have passed on Earth. As a Martian colonist, should I rest every seventh Martian ...
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How can constant creation of new stars explained theologically?

"... we get on average about one new star per year, and one star dying each year as a planetary nebula in the Milky Way.... therefore there are about 275 million [born] per day, in the whole ...
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Has the number of the tribes of Israel anything to do with the universe/stars/planets?

Has the number of the tribes of Israel anything to do with the universe/stars/planets? Maybe the other way around? Is there anywhere in the Talmud or tradition that talks about this question (not ...
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Why did G-d create everything important off-center?

I hope not to argue that the Heliocentric view is true as is our current understanding of [our position in] the Universe, the Earth is rotating around the Sun, that is rotating around the center of ...
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Why did G-d create the Earth spherical?

I hope nobody questions the fact of the spherical Earth. Just as spherical as all other celestial bodies. Many argued whether we knew this fact or not, but I don't recall that those who claim we ...
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How precise were the Temples' directions (East/North)

Calculating the true astronomical North/South is very simple - find the longest way and cast a shadow. Are there sources on how precise those directions in the Temples were? Are there special Jewish ...
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Biblical description of the firmament vs. round earth in the Zohar

Zohar Vaikra 10a [quotes the Book or Rabbi Hamnunab Sabah]: וּבְסִפְרָא דְּרַב הַמְנוּנָא סָבָא, פָּרִישׁ יַתִּיר, דְּהָא כָּל יִשׁוּבָא מִתְגַּלְגְּלָא בְּעִגוּלָא כַּכַּדּוּר, אִלֵּין לְתַתָּא, ...
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How do the outer planets: Uranus, Neptune and Pluto fit into Judaism?

It is not a secret that we discover new things in all fields of science, not mentioned in our sources all the time. We know that in Judaism the 7 planets represent/aligned with 7 spiritual forces and ...
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Does Judaism differentiate between a planet and a star?

On the 4th day, G-d created Sun, Moon and the stars. Besides the Moon, Mercury, Venus, Mars, Jupiter, and Saturn were known since ancient times (not mentioning the existence of the real stars). ...
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Aurora Borealis in Midrashim

We see many fascinating works of Hashem around the world and one of which is Aurora Borealis. Do our midrashim or books on mysticism have anything to say about its origin or anything related to it?
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Rabbinical sources that support the Flat Earth view

While many people are busy looking for the slightest hints of the vast scientific knowledge possessed by our Sages, I've bumped into Rasa"G's interpretation of Sefer Hayetzirah 4,2 (c.900) (is there ...
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Sources for the Earth revolving round the sun

Are there any Jewish writings that suggest the Earth revolves around the sun and is not the center of the universe?
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For the start of the day, is "sunset" astronomical or visible?

Yesterday was the equinox and I noticed that the day was longer than 12 hours according to the (secular) sunrise/sunset times. Curious, I did some investigation. One reason for the difference is how ...
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2 votes
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Keeping Two-day Shabbos in the Pacific Islands? [duplicate]

What's this I see about people in the Pacific Islands keeping two days of Shabbos? If it is true: Who, how, since when, and why?
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Counting and naming the stars

Why does Hashem count and name the stars in Heaven? This is mentioned in the first Rashi on Shemot, see below. I would like an explanation on this... Quote from Rashi: And these are the names of the ...
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Photographing an Eclipse

There is a general prohibition on depicting and/or owning depictions of celestial bodies, such as the sun and moon (see, e.g., the Rambam Hilkhoth Avoda Zara 3:18). Nonetheless, there are opinions ...
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9 votes
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Is there any evidence that Chazal knew what caused eclipses?

Many ancient cultures believed that eclipses are caused by things other than syzygy. The Egyptians had Apophis. The Hindus had Rahu. (The interested reader can see more here.) In light (ha) of the ...
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Parameters of the bad omen for eclipses

The Gemara in Succah 29a says that solar eclipses are bad omens for the nations, while lunar eclipses are bad omens for the Jews. The Gemara compares an eclipse to a king who leaves his guests sitting ...
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The moon in the future [duplicate]

We say in Kiddush Levanah, יהי רצון מלפניך...למלאת פגימת הלבנה ולא יהיה בה שום מיעוט May it be Your will...to fill the reduction of the moon, and that there should be no diminishment in it. ...
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6 votes
1 answer
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Source for Seforno that the Earth was tilted at the time of the Flood

In Oorah's 2009 Shmorg video, one of the tracks is about Birchat Hachama, and at around the 10 minute mark, the narrator states the following (I'm paraphrasing): The Sforno writes that before the ...
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Why did Hashem create only one planet (Earth) in the whole entire universe that can support intelligent life

Is there any rabbinic literature explaining why Hashem created only one planet (Earth) in the whole entire universe that can support intelligent life?
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2 votes
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Is there lunar drift in the fixed Hebrew calendar?

It is known that there is a slight discrepancy in the average length of a year according to the Hebrew calendar and the average length of an astronomical solar year which causes a seasonal drift in ...
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2 votes
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Shooting Stars and Luck

There seems to be a non-Jewish association of good luck with seeing a shooting star. Is there any source for this in Judaism?
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8 votes
5 answers
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What is the firmament?

In Genesis 1:6-8 the firmament and its creation are mentioned for the first time: And God said: 'Let there be a firmament in the midst of the waters, and let it divide the waters from the waters.' ...
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5 votes
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Illustrated hilchot Kiddush Hachodesh

I remember seeing about 20 years ago a beautiful annotated commentary on Rambam's hilchos kiddush hachodesh, with extensive illustrations and calculations, explained according to both ancient and ...
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Minyan, netz hachamoh, and precision in time

There are halachic sources that discuss the importance of davening shemona esrei at netz (at sunrise), some of which state that it is preferable to daven at netz over davening with a minyan (at least ...
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8 votes
1 answer
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Is there any evidence of time-zones in Talmud? (Tanaim and Amoraim only)

There are many verses in the Talmud, Midrash and Siddur that state that the sun and moon rise and set through gates in the firmament. This would imply that there are no time-zones. To this world view ...
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2 votes
1 answer
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Solar Power on Shabbos

What's the deal with using solar power on Shabbos? Cooking is permitted, but what of the following cases: 1) Heating water (Dud-Shemesh style) 2) Solar-powered watches 3) Solar-powered toys What ...
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What's the earliest "acknowledgement" of Heliocentrism in Judaism? [closed]

The English Wikipedia says that Heliocentrism was "official" in Judaism only by the 20th century: In later periods there were no explicit attacks on heliocentrism, although some Rabbis were not ...
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1 answer
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Are star stickers mutar?

Do any contemporary poskim discuss the usage of star stickers with regard to the prohibition of depicting celestial bodies (e.g. the glow-in-the-dark ones people put on walls and ceilings)? What if ...
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15 votes
1 answer
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We're not supposed to point at stars?

I'm an Israeli Jew living in Israel. I often give "sky tours" where I show children and adults different stars and a view through a powerful binocular at objects of interest. Recently a young boy ...
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4 votes
2 answers
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What time is sunset?

Is sunset (Shkiya) the time the sun hits the horizon or when it sunk completely below it? What about sunrise?
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8 votes
4 answers
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How accurate is the Molad?

To the best of my knowledge the Molad is every 29.5 days + 793 Chalakim. Is there any information showing if the current Molad calculation is accurate scientifically? If it is off by how much is it ...
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8 votes
3 answers
223 views

Depicting a constellation

Assuming the intention is at least partly for educational purposes, Is it mutar to arrange star stickers in the form of actual constellations (say, on a ceiling) or is that included in the prohibition ...
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1 vote
1 answer
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Where does Rashi say that Jews will be revered for knowledge of astronomy?

I remember reading a Rashi that says that the Jews will be revered for their knowledge of the stars. What's the location of this Rashi?
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-2 votes
1 answer
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Does the verse in Tehillim 147:4 imply that one cannot name a star after a person?

Usually, around Mother's Day and Valentines Day, I hear a radio commercial suggesting that, as a gift to your loved one, you can name a star after him / her. (Amazing gimmick - no inventory!!) In ...
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9 votes
4 answers
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Why did Hashem create the world in such a way that a leap year is needed?

I understand why we have a leap year; to keep the sun and moon cycles in sync, so that Pessach is always in the spring. That's all technical, as a result of the moon orbiting too slowly - or the sun ...
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6 votes
1 answer
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Counting years according to the solar calendar

I once heard there is an opinion in Rishonim (maybe Gaonim?) that says we count ones years of life according to the solar calender. So for example a boy would become bar mitzvah when he would turn 13 ...
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What does "shachar" in "alos hashachar" mean?

We find a number of terms referring to when morning starts and then perhaps a similar term used to refer to the time of shachris. Alos HaShachar (עלות השחר) Ayeles HaShachar (אילת השחר) and Shacharis ...
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9 votes
1 answer
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What b'racha do you say on seeing the Aurora Borealis (if any)?

If one is so lucky as to see the Aurora Borealis (northern lights) or its southern equivalent, does one say a b'racha? If so which one? I've heard that oseh ma'aseh v'reishit applies to comets and ...
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11 votes
4 answers
740 views

Plants before the Sun in the Order of Creation

Why does plant life precede the Sun in the order of creation given that plants need the Sun to do photosynthesis?
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4 votes
2 answers
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Conservative Kiddush Levanah

The version of Kiddush Levanah printed in the Conservative movement's siddur omits the verse "כשם שאני רוקד כנגדך..." I've heard that this is because the Conservative movement believes that in an age ...
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4 votes
3 answers
486 views

Stars are living creatures?

the Rambam in yesodei torah says that stars are creatures with intellect. how do we reconcile this with modern science which says that they are merely inanimate balls of hydrogen and helium gas.
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9 votes
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How many stars did Rashi think there were?

According to the Chabad translation, Rashi on Deut. 1:10 implies that there are more than 600,000 stars: The Lord, your God, has multiplied you, and behold, you are today as the stars of the ...
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