<p>According to <a href="https://webb.nasa.gov/content/about/orbit.html" rel="noreferrer">NASA</a>, the JWST is 1.5 million kilometers away, which is about <strong>5 light seconds</strong>.</p>
<p>For comparison, the distance to the Moon is about 1.3 light seconds, Mars ranges from about 3 to 22 minutes, and to the Sun is 8 minutes.</p>

CC BY-SA 4.0
2022-07-19T00:17:32.277Z
2022-07-19T00:17:32.277Z
Zamicol
<p>Almost 5.1 seconds, plus or minus around 1 second.</p>
<p>Here's a daily plot (at midnight) of the light travel time from the JWST to the centre of the Earth, courtesy of JPL Horizons, using a script derived from the one in <a href="https://astronomy.stackexchange.com/a/49267/16685">this answer</a>. There are more graphics &amp; scripts related to the JWST <a href="https://astronomy.stackexchange.com/a/49616/16685">here</a>. Times are in <a href="https://en.wikipedia.org/wiki/Barycentric_Dynamical_Time" rel="noreferrer">TDB</a>.</p>
<p><a href="https://i.sstatic.net/chtOi.png" rel="noreferrer"><img src="https://i.sstatic.net/chtOi.png" alt="Light travel time from JWST to Earth, 2022-2024" /></a></p>
<p>The light travel time to a location on the Earth's surface has a small extra variation due to the Earth's rotation. And of course, you can't get a direct line of sight signal from the JWST when you're on the wrong side of the Earth. ;)</p>
<p>Here's an hourly plot for today of the distance from the JWST to its control centre, the  <a href="https://www.stsci.edu/" rel="noreferrer">Space Telescope Science Institute</a>, which is located on the Johns Hopkins University campus. I used longitude -76.622987, latitude 39.332887, altitude 0.073 km as the coordinates.</p>
<p><a href="https://i.sstatic.net/vg9kX.png" rel="noreferrer"><img src="https://i.sstatic.net/vg9kX.png" alt="Light travel time, JWST to StSci, 2022-Jul-19" /></a></p>
<p>Here's my <a href="https://sagecell.sagemath.org/?z=eJyVWG1z2kgS_s6vmCi5Q3JAxhAnMVfULXbkWmeNoYAklcOcaoxGoFjS6DQjG-Lyf9_uGUlIOLtV5yoQ09PT0y9Pv8iGYZApk2nAHhhJabxm5J8kDNYbSWRKH1hIZBAx4lFJiZ_yiPzO0-AnjwXxeUookTRdM0nuuLdrEPijsQcfwu8ESx-CeE1WLJYsVfQk5CB1w17Ktxvq8Lc0kJLF5G5HJiPSneL5bqd7YnfO7JMzxfIlAVWYh-Su3Tm1O-8UecS9wA-Ajlq9VF9zf0AhhmE0GkGU8FSSlLXg87-MCSkayjo_i1eS81CQnCVMM3dFVxum9yMq0YowuLNlsLoHw3K-2YqGNL3kKXCAvY2GX_wkg8NNMxNs7PuCycElDQWzGo0sDYHP2EiZiP7xsRCe_SMJ7ZgKaq_5wzFNguNN7nnXD0JmA8VowJf7wFIR8BiPg6PAuDsqmLuKPKSAsaPhH47rTH53RkBofndmzYZaufPvEwdJX52L-XgK5PGXufvl5mo-Q-ofo_anZmPqXLqT6-GNYrycDkeOps2-z-Za4NXF9LLZABnuxXg6RcrN-MbRlOvhuXM90zRN-eRcz4fuvCBdzL66l-PpaDgvdRuff3Y_DefD6qn58PxaafC-qeP3WxkWM6JbEfxkgyCWZs-yGh7zic_kauMiZk2Nz1YOwxYRQJD44Al-s8TqKwBpf_ko_dWbN7PxZeOp8ONz42I8Gg1vPqEGT1rgM-ju3MwdZfCTFg60V3viivPU-613dgbU2dXcAfeMp58GzfaH9_b7bvfs44dW78zu9bof4VcHwNlrNmbz4XTuzq9GytgnpeszkseTKpUniuhM3NnVfwoiQyKo7oDqaAUa9TpJ0S1gg6XWgHXgLhBvJ1xIE5DXUuk9eGpqzDb7pCnZVjafWwShJmAniJMMN8wmCGu20F3Wsxa6x1_KbMFoutqYqTGcXJGvznR2Nb7p34oj83Z2ZBkq22yUbdnrlGeJeaJlBH4p5tWAVFCtg4N_2hTf-EbTGOpCn-ANxaFAkKf8Nyh9l2GZAZpYpUEicRfLwlNF7rNh6ZITHeht_ltYt29uAQGOaR-pn87YqWpeKByh3Bses0MdjZsxURnmTK9mhnWwW5ejoyKzNFaiqlGrM4ZBzIQOnqLaIgkDqaim5sgvv40N-wcPYlPtLU77J--XVm6squIDEpXOX5z0l2onL-OHvois_873BZ7ENGIqmvbRrfU34cxr_i-kXeid_0ta7h9UvkXq-QyVIMAnXUmV-BEFwzXLwPj8bTY3Cs6BgblotECiSquBgT2hPaK79omh64EivauQGJBOPHUGm44i9Dot1VKELt2QOlyKwTzN4OcqSx9Y8ZuHHC5dp4zF-lYsUr1uizwGntwM3sEFD-tCCM0kdzPV2vKW0C9gFkPPNPESAhBWN1gvADdjIVtJQqFdMSokASQR7pPaKeMQcI3cuSILMfAvaqYtYCpITKvwYLnO5Sg37pnQg9UVK1dlxuR3_WXacMKSDYtYChx64OBZ7L36C82reHARS4WiaqHAh9dVgY-Pl4mTby6E3jKbraa16LdPlqpqwCSgsacT5bUipvyxIPeLvOaP1r9qCr4mE9zRjoKpCj1EPmdhQPHkTgBJwaqavZcwZPQBfEcoetFZLvrdZS2957xPSMkASmoOncQuVHQXhx6wZlnYpspGvkTdg1ahPoszcDZwmCisAqvXxNlKTCoCgwuLPZoqQeU-UHGNPuaP0EZUqv7i9N7Ylh7K2pg6LT1n5o92WpX8wwNOSG_o1B4WkIUfcipNYe1jAVcuS_7SZJiHEtDUNLUEckQ-vn_X6Sgxx6R7dvbhrGu_O_1o7cFUdEdtDNwJjKGsGTKi90ynu6RRIsodAHNA_lFWBTIYkM7effi3i0CPTYS-zy_I0YU1t7es87ZIBIoCK5zK2Yx2BfbKUhTlkbfQd96S3aLbr8sAjZSedS3yg29hEoS-AAdBo-ICG1AEHaBTl6NMqjlTirJ9ALIQKQW8z7Mg9Mg5-xmwvMhoD8nkAXQNcNIt46ONkRCQHXweOsAQQ6k3gTfvGer8HqqIUViY-oiliTRlmKqdEswAFfDeA-ICJO2N97CkSdKGG_e0LXpQQpR7expqA71ogCodAQsKU88anBHMuZ2oQrmn9AHvmrsORgU-JkiEa72dhbCzUBbe2K1CR5laDxTmEbgDnY4mgyBURUkFgVBQTTRG0bR0pMDCWtZRor1YxA9r0uE1ew-_CEjuzCK8I4a5GwD04xUjd0w-Qi9T72_QvoMi1iHHk0WYsWTliIIJrLaDtSrfilDyQHvvGAwBzjZKqlY63xhprifk7ts9_5kItuKxJ4rZ7TWZqdKKKq1Tmmygt8qNWkY13bHaqxMTkIcLdHLIW4pNuXIT5Itl0brVd0vPXXIXsoHRzzNyghHHOcVUKhq18wfH83c2SUOXQgWMI-hQAyNkviyMuH-EDqZyO1hJMw-MhA7FBr5x_eJNVr2FPlUa3TORnDxV2uDzrR44VIqkQNATSU5Zp4GnbBosFhnEQ2VRljczJsB8I6I_eGoscc5Z3bvle-yge7QoF8tCHt0y4Yb0joUg0dgXfPCKAeESBAVVmFw1B53YJ6f4crFWK_zKXWu7DHuHe__oCVsPRKb2UO6uQI81--xR0Uhg4JXCBIugG-5NKsEHOqibTmvhKQeTg4RUIu9UursJlRtTZ9XB2RyCQ8-rtPFdFMSQRfBSChGd2LjEcQh_0W0xO-1UpQcWKBfq2VbnsFjAi-BpWdyw-kJHKINzoKGCoOozqk5jTfABaspQQ0Q0DI1WJfvzifQupKt7iA68CEF867jUsDIqtv3IYJykIsHxEhp1wNXOVlm5BdVbhxZvS4u32uJfeEGXci0UaudWu2CrXHBcd0mOCgHY1gdcpYXZsT-Ct3IZx3qmztX28_HPKP5fYsOgbWCY4UkAgqyylcRro7gDksxUh0tcwIG9z1Vt4VBXNRPgGzwFKhC_XsqxxmxkFJq-DfXNK-ZfseGP5sT6EzxjrH0=&amp;lang=sage" rel="noreferrer">plotting script</a>, running on the SageMathCell server.</p>

CC BY-SA 4.0
2022-07-19T09:16:53.590Z
2022-07-21T08:42:17.777Z
2022-07-21T08:42:17.777Z
PM 2Ring
<p>The processing for <a href="https://jwst-docs.stsci.edu/jwst-observatory-hardware/jwst-wavefront-sensing-and-control" rel="noreferrer">JWST's alignment</a> is done on Earth. How long does it take for a signal from Earth to reach the JWST?</p>

CC BY-SA 4.0
2022-07-20T23:13:27.843Z
What did your own research leave unclear, please?
Robbie Goodwin
CC BY-SA 4.0
2022-07-28T22:29:09.300Z
@PM2Ring If that's true, why can you not here and now re-state them?
Robbie Goodwin
CC BY-SA 4.0
2022-07-28T23:14:58.097Z
@PM2Ring What do you mean? I saw a link to JWST's alignment, leading nowhere useful. What did I miss?

How "How long does it take for a signal from Earth to reach the JWST?" belongs to Astronomy, rather than, EG, aerospace or astronautics is up to you.

What difference do you see between "How many light seconds…" and "How far…"?

Google tells us it's about 1.5 million km; NASA's and other specialist WWW will give better answers.

Isn't that about 5.003 light seconds, ignoring the huge room for error in "5.1 +/- 1" in PM 2Ring's Answer?

Is anything there humorous?
Robbie Goodwin
CC BY-SA 4.0
2022-07-29T21:28:28.610Z
@PM2Ring So sorry. I skipped over that as someone echoing my own thoughts; ie, how could it not be the next worst thing to self-evident?
Robbie Goodwin
CC BY-SA 4.0
2022-07-29T22:35:38.223Z
@Robbie Ok. :) I guess we should delete this stuff.
PM 2Ring
CC BY-SA 4.0
2022-08-05T23:11:19.233Z
If that's what you'd like why not go ahead and delete everything?
Robbie Goodwin
<time><james-webb-space-telescope>
How many light seconds away is the JWST?
Zamicol
# How many light seconds away is the JWST?

(Asked by: username_0 on 2022-07-19)

The processing for [JWST's alignment](https://jwst-docs.stsci.edu/jwst-observatory-hardware/jwst-wavefront-sensing-and-control) is done on Earth. How long does it take for a signal from Earth to reach the JWST?

**Tags:** time, james-webb-space-telescope

> **Comments:**
> **username_1**: What did your own research leave unclear, please?  
> **username_1**: @username_2 If that's true, why can you not here and now re-state them?  
> **username_1**: @username_2 What do you mean? I saw a link to JWST's alignment, leading nowhere useful. What did I miss?  How "How long does it take for a signal from Earth to reach the JWST?" belongs to Astronomy, rather than, EG, aerospace or astronautics is up to you.  What difference do you see between "How many light seconds…" and "How far…"?  Google tells us it's about 1.5 million km; NASA's and other specialist WWW will give better answers.  Isn't that about 5.003 light seconds, ignoring the huge room for error in "5.1 +/- 1" in PM username_2's Answer?  Is anything there humorous?  
> **username_1**: @username_2 So sorry. I skipped over that as someone echoing my own thoughts; ie, how could it not be the next worst thing to self-evident?  
> **username_2**: @username_1 Ok. :) I guess we should delete this stuff.  
> **username_1**: If that's what you'd like why not go ahead and delete everything?  

---

## 2 answers

### Answer by username_2 on 2022-07-19. Score: 37 | Accepted answer

Almost 5.1 seconds, plus or minus around 1 second.

Here's a daily plot (at midnight) of the light travel time from the JWST to the centre of the Earth, courtesy of JPL Horizons, using a script derived from the one in [this answer](https://astronomy.stackexchange.com/a/49267/16685). There are more graphics & scripts related to the JWST [here](https://astronomy.stackexchange.com/a/49616/16685). Times are in [TDB](https://en.wikipedia.org/wiki/Barycentric_Dynamical_Time).

[![Light travel time from JWST to Earth, 2022-2024](https://i.sstatic.net/chtOi.png)](https://i.sstatic.net/chtOi.png)

The light travel time to a location on the Earth's surface has a small extra variation due to the Earth's rotation. And of course, you can't get a direct line of sight signal from the JWST when you're on the wrong side of the Earth. ;)

Here's an hourly plot for today of the distance from the JWST to its control centre, the [Space Telescope Science Institute](https://www.stsci.edu/), which is located on the Johns Hopkins University campus. I used longitude -76.622987, latitude 39.332887, altitude 0.073 km as the coordinates.

[![Light travel time, JWST to StSci, 2022-Jul-19](https://i.sstatic.net/vg9kX.png)](https://i.sstatic.net/vg9kX.png)

Here's my [plotting script](https://sagecell.sagemath.org/?z=eJyVWG1z2kgS_s6vmCi5Q3JAxhAnMVfULXbkWmeNoYAklcOcaoxGoFjS6DQjG-Lyf9_uGUlIOLtV5yoQ09PT0y9Pv8iGYZApk2nAHhhJabxm5J8kDNYbSWRKH1hIZBAx4lFJiZ_yiPzO0-AnjwXxeUookTRdM0nuuLdrEPijsQcfwu8ESx-CeE1WLJYsVfQk5CB1w17Ktxvq8Lc0kJLF5G5HJiPSneL5bqd7YnfO7JMzxfIlAVWYh-Su3Tm1O-8UecS9wA-Ajlq9VF9zf0AhhmE0GkGU8FSSlLXg87-MCSkayjo_i1eS81CQnCVMM3dFVxum9yMq0YowuLNlsLoHw3K-2YqGNL3kKXCAvY2GX_wkg8NNMxNs7PuCycElDQWzGo0sDYHP2EiZiP7xsRCe_SMJ7ZgKaq_5wzFNguNN7nnXD0JmA8VowJf7wFIR8BiPg6PAuDsqmLuKPKSAsaPhH47rTH53RkBofndmzYZaufPvEwdJX52L-XgK5PGXufvl5mo-Q-ofo_anZmPqXLqT6-GNYrycDkeOps2-z-Za4NXF9LLZABnuxXg6RcrN-MbRlOvhuXM90zRN-eRcz4fuvCBdzL66l-PpaDgvdRuff3Y_DefD6qn58PxaafC-qeP3WxkWM6JbEfxkgyCWZs-yGh7zic_kauMiZk2Nz1YOwxYRQJD44Al-s8TqKwBpf_ko_dWbN7PxZeOp8ONz42I8Gg1vPqEGT1rgM-ju3MwdZfCTFg60V3viivPU-613dgbU2dXcAfeMp58GzfaH9_b7bvfs44dW78zu9bof4VcHwNlrNmbz4XTuzq9GytgnpeszkseTKpUniuhM3NnVfwoiQyKo7oDqaAUa9TpJ0S1gg6XWgHXgLhBvJ1xIE5DXUuk9eGpqzDb7pCnZVjafWwShJmAniJMMN8wmCGu20F3Wsxa6x1_KbMFoutqYqTGcXJGvznR2Nb7p34oj83Z2ZBkq22yUbdnrlGeJeaJlBH4p5tWAVFCtg4N_2hTf-EbTGOpCn-ANxaFAkKf8Nyh9l2GZAZpYpUEicRfLwlNF7rNh6ZITHeht_ltYt29uAQGOaR-pn87YqWpeKByh3Bses0MdjZsxURnmTK9mhnWwW5ejoyKzNFaiqlGrM4ZBzIQOnqLaIgkDqaim5sgvv40N-wcPYlPtLU77J--XVm6squIDEpXOX5z0l2onL-OHvois_873BZ7ENGIqmvbRrfU34cxr_i-kXeid_0ta7h9UvkXq-QyVIMAnXUmV-BEFwzXLwPj8bTY3Cs6BgblotECiSquBgT2hPaK79omh64EivauQGJBOPHUGm44i9Dot1VKELt2QOlyKwTzN4OcqSx9Y8ZuHHC5dp4zF-lYsUr1uizwGntwM3sEFD-tCCM0kdzPV2vKW0C9gFkPPNPESAhBWN1gvADdjIVtJQqFdMSokASQR7pPaKeMQcI3cuSILMfAvaqYtYCpITKvwYLnO5Sg37pnQg9UVK1dlxuR3_WXacMKSDYtYChx64OBZ7L36C82reHARS4WiaqHAh9dVgY-Pl4mTby6E3jKbraa16LdPlqpqwCSgsacT5bUipvyxIPeLvOaP1r9qCr4mE9zRjoKpCj1EPmdhQPHkTgBJwaqavZcwZPQBfEcoetFZLvrdZS2957xPSMkASmoOncQuVHQXhx6wZlnYpspGvkTdg1ahPoszcDZwmCisAqvXxNlKTCoCgwuLPZoqQeU-UHGNPuaP0EZUqv7i9N7Ylh7K2pg6LT1n5o92WpX8wwNOSG_o1B4WkIUfcipNYe1jAVcuS_7SZJiHEtDUNLUEckQ-vn_X6Sgxx6R7dvbhrGu_O_1o7cFUdEdtDNwJjKGsGTKi90ynu6RRIsodAHNA_lFWBTIYkM7effi3i0CPTYS-zy_I0YU1t7es87ZIBIoCK5zK2Yx2BfbKUhTlkbfQd96S3aLbr8sAjZSedS3yg29hEoS-AAdBo-ICG1AEHaBTl6NMqjlTirJ9ALIQKQW8z7Mg9Mg5-xmwvMhoD8nkAXQNcNIt46ONkRCQHXweOsAQQ6k3gTfvGer8HqqIUViY-oiliTRlmKqdEswAFfDeA-ICJO2N97CkSdKGG_e0LXpQQpR7expqA71ogCodAQsKU88anBHMuZ2oQrmn9AHvmrsORgU-JkiEa72dhbCzUBbe2K1CR5laDxTmEbgDnY4mgyBURUkFgVBQTTRG0bR0pMDCWtZRor1YxA9r0uE1ew-_CEjuzCK8I4a5GwD04xUjd0w-Qi9T72_QvoMi1iHHk0WYsWTliIIJrLaDtSrfilDyQHvvGAwBzjZKqlY63xhprifk7ts9_5kItuKxJ4rZ7TWZqdKKKq1Tmmygt8qNWkY13bHaqxMTkIcLdHLIW4pNuXIT5Itl0brVd0vPXXIXsoHRzzNyghHHOcVUKhq18wfH83c2SUOXQgWMI-hQAyNkviyMuH-EDqZyO1hJMw-MhA7FBr5x_eJNVr2FPlUa3TORnDxV2uDzrR44VIqkQNATSU5Zp4GnbBosFhnEQ2VRljczJsB8I6I_eGoscc5Z3bvle-yge7QoF8tCHt0y4Yb0joUg0dgXfPCKAeESBAVVmFw1B53YJ6f4crFWK_zKXWu7DHuHe__oCVsPRKb2UO6uQI81--xR0Uhg4JXCBIugG-5NKsEHOqibTmvhKQeTg4RUIu9UursJlRtTZ9XB2RyCQ8-rtPFdFMSQRfBSChGd2LjEcQh_0W0xO-1UpQcWKBfq2VbnsFjAi-BpWdyw-kJHKINzoKGCoOozqk5jTfABaspQQ0Q0DI1WJfvzifQupKt7iA68CEF867jUsDIqtv3IYJykIsHxEhp1wNXOVlm5BdVbhxZvS4u32uJfeEGXci0UaudWu2CrXHBcd0mOCgHY1gdcpYXZsT-Ct3IZx3qmztX28_HPKP5fYsOgbWCY4UkAgqyylcRro7gDksxUh0tcwIG9z1Vt4VBXNRPgGzwFKhC_XsqxxmxkFJq-DfXNK-ZfseGP5sT6EzxjrH0=&lang=sage), running on the SageMathCell server.


---

### Answer by username_0 on 2022-07-19. Score: 26

According to [NASA](https://webb.nasa.gov/content/about/orbit.html), the JWST is 1.5 million kilometers away, which is about **5 light seconds**.

For comparison, the distance to the Moon is about 1.3 light seconds, Mars ranges from about 3 to 22 minutes, and to the Sun is 8 minutes.


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